Welcome to Part 7 and the last article in our series on physicalism (the theory that the physical world can fully explain consciousness).

If you're new here, hello and welcome! I’m glad you’re here. This article is part of a series, and it will draw heavily on concepts covered in earlier articles. If you are new to the philosophy of mind, you may find the earlier articles helpful for understanding this one.

1. Physicalism: Are You Just a Brain?

2. What Exists and What is Imagined?

3. Identity Theory: The Mind is the Brain

4. Functionalism: The Mind is What the Brain Does

5. Functionalism: Why the Most Popular Consciousness Theory Might be Wrong

6. Does the Mind Exist? Understanding Eliminative Materialism

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We've explored a lot in this series, but at the centre of all of it is one key question:

How do our thoughts, feelings, beliefs and choices fit in a world made of physical stuff?

Our thoughts and decisions don't feel like they're just the result of neurons firing in our brains. Mental events, we assume, are surely more than just a complex series of physical events.

And yet, if we want a physicalist theory, we are going to have to ground those mental events in the physical world.

In this series, we’ve explored functionalism, reductionism, and eliminativism as possible ways to account for mental events as physical phenomena. But for many, these theories do not provide a satisfying answer. This is particularly true when it comes to trying to account for the specialness of our experiences and our sense of mental agency.

Enter non-reductive materialism.

This theory offers a different approach to the mind-body problem. It tries to explain our intuitions about consciousness within the scientific view of physicalism.

But does it succeed?

To find out, let's ask three questions:

1. What is non-reductive materialism?

2. Why might someone believe in non-reductive materialism? and,

3. What are the main arguments against non-reductive materialism?

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Q1: What is non-reductive materialism?

The philosopher Donald Davidson is usually seen as the main thinker behind non-reductive materialism (his theory is called anomalous monism).

To answer the question — what is non-reductive materialism — we need to get our heads around two things:

1. the concept of supervenience and,

2. Davidson’s Three Principles

Let’s take these in turn.

What is Supervenience?

Supervenience is a technical term philosophers like to use when navigating tricky philosophical terrain.

Formally, it is defined as:

a relationship between two sets of properties where one set (A) supervenes on another set (B) if and only if there can be no difference in A without there being a difference in B.

Let’s unpack it.

At its core, supervenience is a way of describing how some properties depend on other properties.

Imagine an image of a piece of cake on your computer screen. This image depends on the arrangement of pixels that make up the image. The image of the cake cannot change (to say, an image of an umbrella) without changing some of the pixels. So, we say the image of the cake supervenes on the arrangement of the pixels because the image of the cake cannot change without there being a change in the pixels.

In the philosophy of mind, many philosophers, Davidson included, argue that the mind supervenes on the brain.

If you have a thought that it will rain today, this mental event is associated with a specific physical event in your brain, such as a particular pattern of neural activity. If your thought about rain suddenly changed to a thought about remembering your umbrella, there would necessarily be some corresponding change in your brain's neural activity.

The Three Principles

In his classic 1970 paper Mental Events, Davidson outlines three principles. He argues that we intuitively believe all three of these principles to be true, even though they seem logically inconsistent.

Let’s review each principle, and then we’ll examine the potential contradiction.

Principle 1: Mental events can cause physical events.

Intuitively, we think that our beliefs and desires cause our actions. For example, my belief that it would rain today and my desire to stay dry caused me to grab my umbrella before leaving home.

Principle 2: all causal relationships are governed by strict, deterministic laws.

This is a universally accepted principle in physics.

We understand that physical events (like releasing a ball from a height) can cause other events to happen (like the ball falling to the ground). For this causal effect to happen, there must be a law-like regularity that connects the initial event (releasing the ball) with the proceeding event (the ball falling — in this case, it’s the law of gravity).

Principle 3: there are no psychophysical laws

When we think about why people do things, we don't usually break it down into strict cause-and-effect relationships, like we do with physics. Instead, we like to paint a bigger picture. We make sense of ourselves and others' behaviour by assuming that we think and make choices that are not strictly determined by physical processes.

So, while we might accept that physical events, like balls falling, are predictable based on strict deterministic laws, there doesn't seem to be a comparable set of laws that allow us to predict mental events (like thoughts and decisions) from physical events or vice versa.

The three principles seem to be logically inconsistent.

If I have a mental event, say a belief that it will rain today, that causes a physical act, say I grab an umbrella before leaving the house, then according to Principle 2, the causal relationship between my belief and my physical act must be governed by strict deterministic laws.

But! This would contradict Principle 3, which states that no such laws exist.

It seems we have a problem!

We can’t simultaneously uphold both Principle 1 and Principle 2 while maintaining Principle 3.

But Davidson thinks we can.

He claims we can have our Principle 3 and be physicalists, too.

He does this by claiming a special type of supervenience.

Davidson accepts supervenience — mental events can't change without a change in the brain's neural activity. But, he argues, that the supervenience relationship between the mental and the physical does not imply reducibility. In other words, while Davidson agrees there is a close relationship between the mind and the brain, he also claims the mind cannot be reduced to or fully explained by the brain.

Q2: Why might someone believe in non-reductive materialism?

One way to resolve the logical inconsistency of the Three Principles is to find a Principle that, when rejected, resolves the inconsistency.

Many physicalists would accept Principle 1 (mental events can cause physical events) and Principle 2 (all causal relationships are governed by strict, deterministic laws), as these align more closely with standard physicalist views.

It’s Principle 3 (there are no psychophysical laws) that physicalists will often question.

But Davidson argues that we should accept all three principles, including the potentially contentious Principle 3, and he offers three compelling reasons for doing so.

Folk Psychology

Davidson's first argument for accepting Principle 3 comes from our everyday understanding and use of mental concepts like beliefs, desires, and intentions. We discussed this everyday commonsense idea of mental concepts in the article on eliminative materialism — there, we referred to these concepts as folk psychology.

Davidson argues that while we might understand that a specific mental event is identical to a specific brain event, it does not follow that we could predict or explain mental events as a class — like beliefs, desires, and intentions.

So, in principle, science might (one day) be able to predict and explain the specific belief I had about rain at 9 AM this morning with the specific brain event I had at the same moment. But science can’t explain beliefs as a class or mental concept.

Our typical interest in folk psychology relates to classes or concepts like desires, habits, knowledge, and perceptions. We use these concepts to explain and predict behaviour. Davidson argues that science can't explain folk psychological concepts or reduce them to purely physical facts.

Free Will

Davidson's second argument for accepting Principle 3 relates to free will and human agency.

If mental events are governed by strict, deterministic laws in the same way that physical events are, it’s difficult to conceive of how human actions could ever be truly free. For instance, if every thought or decision could be perfectly predicted by knowing the exact state of our brain, it would be difficult to argue that we genuinely have free will.

By accepting Principle 3, Davidson leaves room for some unpredictability and spontaneity in mental events, which he sees as crucial for free will.

The Is-Ought Distinction

Davidson's third argument for accepting Principle 3 uses the is-ought distinction as an analogy.

The is-ought distinction, first pointed out by philosopher David Hume, says that we can't figure out what ought to happen simply by looking at what is.

Here's an example: Imagine a study that shows 90% of people jaywalk at a particular intersection. That's a fact about what is happening. But this fact alone doesn't tell us what ought to happen or what's right or wrong. We can't use only this information to decide if people ought to jaywalk or if the city ought to build a crosswalk. To make those 'ought' statements, we'd need additional moral reasoning or values.

Davidson applies this idea to the mind-body problem. In ethics, while facts can inform our moral judgments, we generally agree that we can't derive 'ought' statements purely from 'is' statements. We can't say jaywalking ought to be illegal just because we know jaywalking happens.

Davidson uses this widely accepted idea as an analogy. He suggests that, similarly, we can't fully explain or reduce mental concepts (like beliefs or decisions) to physical events in the brain, even if we believe mental events have a physical basis. Just as we can't get 'ought' from 'is', we can't get 'mind' entirely from 'brain'.

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Q3: What are the main arguments against non-reductive materialism?

Non-reductive materialism faces several criticisms. But I want to focus on one argument from philosopher Jaegwon Kim.

To understand Kim’s argument, we need to understand one more term:

Overdetermination

Overdetermination occurs when an event is claimed to have more than one sufficient cause — a sufficient cause is a cause that, on its own, is enough to have the effect.

A classic example is a firing squad: if five shooters all accurately fire at a target simultaneously, and any one of their shots would have been sufficient to cause death, then the death is overdetermined. Each shot is a sufficient cause, yet they all occur together.

Overdetermination is typically found and accepted in thought experiments about moral events. But in physics, explaining events through overdetermination is generally considered to be a problem. This is because it violates the principle of parsimony (also known as Occam's Razor), which suggests that simpler explanations should be preferred over complex ones. It also challenges the idea of causal sufficiency — if one cause is truly sufficient, additional causes are, by definition, unnecessary.

In the case of the firing squad example, overdetermination is typically accepted because of moral and legal concerns: responsibility is distributed among all members of the firing squad, avoiding singling out any one individual as solely responsible for the death. This is a rare case where overdetermination is intuitively acceptable.

But in physics, it is generally accepted that every physical event that has a cause has no more than one sufficient physical cause. This claim is based on the principle of the causal closure of the physical domain. For example, consider a row of dominos falling. The physical event of each domino falling has a sufficient physical cause: the previous domino hitting it. We don't need any additional causes to explain the dominos falling.

Let's see how Kim uses overdetermination to challenge non-reductive materialism.

The Argument from Overdetermination

Kim argues that non-reductive materialism leads to a form of overdetermination that is typically considered to be a problem. Here's how the argument unfolds:

Let's suppose you have a specific mental event of the desire to open your umbrella. This mental event is associated with a specific physical event in your brain.

Now, let’s suppose your desire to open your umbrella causes the physical event of opening your umbrella.

According to the principle of the causal closure of the physical domain, because opening your umbrella is a physical event that has a cause, whatever caused you to open your umbrella must be a sufficient physical cause. We know that you opened your umbrella because of your desire to open your umbrella — so the sufficient physical cause would be the specific physical event in your brain associated with your desire to open your umbrella.

We have a problem!

The physical act of opening your umbrella is overdetermined — you have two allegedly sufficient causes for opening your umbrella: (1) the mental event of the desire to open your umbrella and (2) the specific physical event in your brain.

Given the causal closure of the physical, the specific physical event in your brain is sufficient to cause you to open your umbrella.

So, to resolve this, we must conclude that while the specific physical event in your brain is the ‘true’ cause of opening your umbrella, your desire to open your umbrella did not actually cause you to open your umbrella, despite appearances.

This renders your desire to open your umbrella causally useless — it appears to cause you to open your umbrella, but the real causal work is done entirely by the specific physical event in your brain.

Any mental event that appears to cause a physical event but actually has no causal power is the definition of an epiphenomenon.

So, do we accept epiphenomenalism?

Kim argues that’s one option. But there are two other options he thinks we could also consider.

The mental event of your desire to open your umbrella could be identical to the specific physical event in your brain.

This means we would accept reductive materialism — mental events can be fully explained by physical events.

Alternatively, if we accept that mental events don’t do anything, we might wish to reject the whole idea of mental events altogether. This would mean accepting eliminative materialism — mental events don’t exist.

So, Kim's argument, if we accept it, puts us in a tricky situation. Every time we try to accept non-reductive materialism, we end up with either epiphenomenalism, reductivism, or eliminativism. Kim's argument suggests that we can't have it both ways — we can’t have both a physically based theory and irreducibility — we must either reduce the mental to the physical, eliminate it altogether, or accept that it has no causal power.

Potential Consequences of Kim’s Argument

Kim's argument (again, if we choose to accept it) seems not just to challenge the logical coherence of non-reductive materialism, but it also raises questions about the very things that we mentioned in Question 2 that we might have intuitively found rather appealing.

What happens to our folk psychological concepts if we accept Kim's argument? Do things like beliefs, desires, and intentions become causally inert? If so, does this mean folk psychology loses its ability to explain and predict human behaviour — which is the very reason for asserting folk psychology in the first place?

And what about free will? Without a distinct mental level, how can beliefs, desires, and intentions have any genuine causal effects? Is there no room for free will? If so, how do we explain agency and moral responsibility?

What about the is-ought distinction? The analogy with the is-ought distinction becomes strained if we accept that the mental can be fully reduced or eliminated. So, if we question the analogy, should we also question the is-ought distinction itself?

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Defining consciousness feels like the easiest and the most difficult of tasks.

It feels easy because consciousness seems self-evident. We all know what it's like to be conscious, to experience the world around us, to feel our emotions and think our thoughts. As philosopher Thomas Nagel famously put it, "...the fact that an organism has conscious experience at all means, basically, that there is something it is like to be that organism."

Yet, paradoxically, defining consciousness becomes challenging — sometimes painfully so — when we approach it scientifically or philosophically. Attempts to pin it down often ignite heated debates that frequently end in stalemates.

It doesn’t help that we use the same word to mean different things. We toss all sorts of things into the consciousness bucket! Of course, we throw in our perceptual experiences: sights, sounds, smells, touch and tastes. Then we fling in mental imagery and imagining in too. Bodily feelings like hunger or an itchy nose get lobbed in. Into the bucket goes emotions, memories, wants, and beliefs. Oh! and don't forget that little voice in your head, always chattering away — that goes in as well. And let's not overlook states of consciousness, from meditation and hypnosis to sleep and psychedelic experiences. But we're not done yet! Our bucket also holds the diagnostic use. Is the patient conscious? not conscious? in a coma? And just to make things really messy, we fling big ideas like raising environmental consciousness in too. No wonder our consciousness bucket is hard to make sense of.

When we use the same word to mean several different things, confusion seems inevitable.

So, we should start to unpack what we mean when we talk about consciousness, especially as it is used in the sciences and philosophy.

We’ve been exploring different philosophical perspectives (and will continue to do so). But this week, let's start exploring how science approaches consciousness.

Studying consciousness scientifically is an unusual thing to do. Science likes to study objective, measurable phenomena, and consciousness is (usually considered) subjective. To sidestep this little problem, scientists adopted the pragmatic approach of referring to any scientific study of consciousness as an investigation into the neural correlates of consciousness (or NCCs) rather than simply the scientific study of consciousness. This was a strategic move. It allowed researchers to focus on questions about how consciousness works without getting bogged down in the philosophical debate about what consciousness is.

For this reason, definitions of consciousness in science tend to be operational rather than philosophical. This pragmatic approach has led scientists to separate the study of consciousness into different approaches.

For example, neurologist Antonio Damasio separates consciousness into core consciousness and extended consciousness.

Core consciousness is the type of consciousness we think about when we think about being awake, alert, and aware. This concept aligns closely with what researchers refer to as states of consciousness, which include not just wakefulness but also sleep states, medical states such as coma, altered states induced by meditation or psychoactive substances, and states of sedation or anesthesia.

Extended consciousness is the contents of our conscious experience. This includes all the various contents that make up our experience. So, it includes things like perceptions, thoughts, feelings, memories, bodily sensations, and mental imagery.

Others like to add a third approach — self-consciousness.

There are many ways scientists break down the problem of consciousness, but

1. States of Consciousness

2. Contents of Consciousness, and

3. Self-Consciousness

is a popular breakdown and not a bad place to start.

Let’s take each in turn.

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1. States of Consciousness

The idea of states of consciousness is closely tied to the idea of arousal. States of consciousness might include states of wakefulness, sleep and anesthesia. But they also include other states, like meditative states, drug-induced states, or changes in consciousness states due to injury. For example, brain injury can cause coma, unresponsive wakefulness syndrome (formerly known as a persistent vegetative state), minimally conscious state, and locked-in syndrome (the devastating condition of full awareness but with almost complete paralysis).

The brain regions thought to be responsible for our states of consciousness are located in the brainstem, which, evolutionarily speaking, is the oldest part of the brain. The brainstem is primarily responsible for regulating our bodies — so things like breathing and regulating sleep-wake cycles. Damage to this area can lead to coma, unresponsive wakefulness syndrome, locked-in syndrome, or death.

Let's focus on sleep as an example of a different state of consciousness.

In everyday language, there’s a tendency to talk about the awake state as being conscious and the sleep state as unconscious. And in some ways, this makes sense. It is only when we are awake that we can consciously experience our world.

But sleep isn't simply a shutdown — it’s a different state of consciousness.

As our understanding of sleep deepens, we're discovering that even during deep, dreamless sleep, our minds aren't completely switched off. In fact, when people are awakened during the deepest stages of sleep, they often report experiencing mundane thoughts.

Researchers are still trying to figure out what goes on during sleep and how sleep is different to being awake. But one study provides some interesting evidence. Participants’ brain activity was recorded while they were awake and while they were sleeping. The researchers used a technique called transcranial magnetic stimulation (TMS), which sends pulses through the skull to stimulate specific areas of the brain. When participants were awake, the TMS pulse spread across the cortex like ripples in a pond. But during sleep, this pulse did not spread widely. The researchers concluded that during sleep, different parts of the brain might not communicate with each other as much as they do when we're awake.

So, we know that even during dreamless sleep, we still have thoughts (a type of content of consciousness). But the specific contents we can experience seem to depend on our current state of consciousness.

You may have noticed this yourself. If you've ever tried to read during a dream, you've likely found it to be a difficult task. The text does not remain consistent. You might be able to read a word or two but try to re-read the same words, and you’ll notice the words have changed. Coherent reading seems to require an awake state of consciousness.

Did you notice that although we started discussing states of consciousness (e.g., sleep) — we've shifted to discussing the contents of consciousness (e.g., thoughts)? This overlap might be inevitable. We’ll get to why later on.

2. Contents of Consciousness

Contents of consciousness are what we are conscious of.

When we think about it, there is a lot we can be conscious of — from basic sensory experiences like sounds, sights, tastes, touches, and smells to complex internal states such as thoughts, feelings, thoughts about feelings, and feelings about thoughts. Contents can even include more nuanced experiences like a vague sense of déjà vu, the sudden realisation that you forgot to buy milk, or the unexpected urge to organise your sock drawer by colour.

The cortex is thought to be primarily responsible for the contents of consciousness. However, the cortex doesn't work alone. It relies on the brainstem (the brain region responsible for our states of consciousness).

Damasio likens the brainstem to a switch, which determines whether we're conscious at all, while the cortex provides the specific content. Without the brainstem keeping us in an awake, conscious state, the cortex can't produce its awake-like contents.

One way to differentiate states of consciousness from contents of consciousness is to consider individuals who might be missing certain content. For example, a person who is blind no longer has vision as part of their contents of consciousness, but we wouldn't consider them any less awake than someone with normal, healthy vision.

For individuals with degenerative diseases, such as Alzheimer's, the contents of consciousness can change dramatically. As the disease progresses, conscious content becomes more limited and significantly different from their pre-illness state. But while their contents of consciousness are profoundly affected, they continue to expereince states of consciousness, like wake and sleep.

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3. Self Consciousness

For most of us, an essential part of experiencing the contents of consciousness is the sense that those contents are experienced by a unified self — an 'I' who does the experiencing.

This sense of self might be responsible for giving us the impression of a unified conscious experience, which is why it's frequently given special status. In psychology and animal cognition research, for example, measures of self-awareness or self-consciousness are often used as indicators of the ‘level of consciousness’.

But many researchers propose that our sense of self is not that special — it’s simply just another content of consciousness.

In fact, anatomically, the sense of self doesn't seem to be a singular thing — it's not localised to a specific region of the brain. It appears that our sense of self is built from many different parts working together. If we lose one of these parts, say through an injury or illness, our sense of who we are can change. The famous case of Phineas Gage is a good example of how the self can dramatically change when brain parts are damaged or missing.

Studies of split-brain patients provide another intriguing example. These patients, who have had the corpus callosum (the main connection between the two brain hemispheres) severed, sometimes display behaviours suggesting two separate selves.

What exactly split-brain patients tell us about our conscious sense of self is still hotly debated. We'll explore the split-brain debate in a future article, but here, I want to raise two other interesting questions.

Does consciousness require a self?

The psychologist Stuart Sutherland argues that,

Many fall into the trap of equating consciousness with self-consciousness — to be conscious it is only necessary to be aware of the external world.

Is Sutherland correct? Does simply being aware suffice for consciousness? Or is there more to it? Does consciousness also require an awareness that we are aware? A meta-awareness?

Ask any long-time meditator, and you’ll receive a resounding — No! Many experienced meditators report states of consciousness without an experiencer, where they have experiences but without the usual sense of being a self.

But this view isn't universally accepted. Some philosophers and cognitive scientists argue that even in these states, there must be some minimal form of self-awareness for the experience to be considered conscious at all.

Does consciousness require content?

At first glance, it might seem obvious that consciousness must always be about something — we're always aware of some sensation, thought, or feeling. This view is known as intentionalism — all mental states are about something.

But is this true?

Is contentless consciousness possible? Can we have a form of consciousness that persists even when all thoughts, perceptions, and emotions — are absent?

Advanced meditative states or psychedelic experiences might have one feeling a sense of ‘nothingness’ or ‘pure being’. Advanced meditators describe such experiences as conscious experiences but without any content.

Critics, however, argue that even these seemingly contentless states must have some minimal content. Perhaps an awareness of time passing or a subtle sense of existing. Maybe what’s being described as contentless is better described as extremely minimal or diffuse content.

The question of whether consciousness requires content has deep implications for answering the philosophical question — what is consciousness?

If we think consciousness always requires content, then we are likely to align our definition of consciousness with intentionalism — consciousness is always about something — or representationalism — conscious experiences represent things in the world or in our minds.

On the other hand, if we think contentless consciousness is possible, we might be more likely to define consciousness as something fundamental — perhaps there is something that underlies all experience that exists even without specific things to be conscious of. This idea might align with certain spiritual traditions and some panpsychist philosophies.

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Thank you.

I want to take a small moment to thank the lovely folks who have reached out to say hello and joined the conversation here on Substack.

If you'd like to do that, too, you can leave a comment, email me, or send me a direct message. I’d love to hear from you. If reaching out is not your thing, I completely understand. Of course, liking the article and subscribing to the newsletter also help the newsletter grow.

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What if everything you think you know about your own mind is an illusion?

Eliminative materialism makes this radical claim. They claim that all your beliefs, desires, thoughts, fears, sensations, and pains — don’t actually exist.

A radical claim is putting it mildly. It seems absolutely absurd!

But despite apparent absurdity, eliminative materialism remains a significant theory discussed in the philosophy of mind.

To find out why, let's ask three questions:

1. What is eliminative materialism?

2. Why might someone believe in eliminative materialism? and,

3. What are the main arguments against eliminative materialism?

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This is Part 6 in our series on physicalism, the theory that the physical world can fully explain consciousness. Here’s what we’ve explored so far:

A quick note before we jump in:

Eliminative materialism was developed by philosopher Paul Churchland. Sometimes, eliminative materialism is attributed to the late Daniel Dennett. While it is true that Dennett and Churchland share similar perspectives, Dennett’s views don’t strictly align with eliminative materialism. So, in this article, I’ll describe Churchland’s view, which is outlined in his classic paper, Eliminative Materialism and Propositional Attitudes.

Q1: What is Eliminative Materialism?

The materialism part of eliminative materialism refers to the idea that all human capabilities can be explained by the physical (material) brain.

The eliminative part refers to the idea of eliminating our common-sense understanding of the mind.

The argument the eliminative materialist makes can be summed up like this:

As we learn about the brain, our commonsense theory of the mind, with its concepts of beliefs, desires, thoughts, pains, and the like, will be shown to be wrong. So, we will eliminate this theory along with its concepts and replace it with a more neuroscientific understanding.

Before we get into the logic of this argument, there's an important distinction to highlight between eliminative materialism and reductionist views (like the mind-brain identity theory).

Reduction vs Elimination

You'll recall that identity theorists are happy to keep concepts like beliefs, desires, thoughts, and pains because they think these mental states really do exist — mental states are simply brain states but at a different level of abstraction. So, the mind-brain identity theory is a reductionist theory — they believe the mind can be reduced to the brain, just like water can be reduced to H₂O.

But the eliminative materialist is an eliminativist theory — they seek to eliminate the mind altogether along with the concepts that go with it, like beliefs, desires, thoughts, and pains.

The Logic of the Argument

Eliminative materialism has two premises:

• Premise 1: Our everyday, common-sense framework of the mind is a theory (Churchland calls this theory folk psychology).

• Premise 2: Folk psychology is a bad theory.

From these two premises, Churchland concludes that because the theory is so fundamentally wrong, it should be eliminated and replaced with a better theory. When a theory is bad, the argument goes, a simple reduction will not work. And Churchland judges the ideas of folk psychology to be ‘too confused and too defective’ to survive reduction.

When discussing Churchland's arguments, it's important to distinguish folk psychology from the modern academic discipline of psychology. By folk psychology, Churchland is referring to our everyday, commonsense understanding of mental states—the intuitive framework we use to explain and predict behaviour based on everyday concepts like beliefs, desires, fears, sensations, pains and intentions.

While Churchland may take issue with the academic discipline of psychology's use of terms that originated in folk psychology, Churchland's critique is aimed at the commonsense notion of mental states, not at the biological explanations given in the academic discipline of psychology.

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Q2: Why Might Someone Believe in Eliminative Materialism?

Let’s examine the strength of the two premises.

Premise 1: Folk Psychology is a Theory

So, what exactly is a theory?

A theory does two things — it tries to explain why something happens, and it tries to predict what might happen in the future.

For example, the theory of gravity explains why objects fall to the ground and predicts how they will behave under different conditions. It explains why planets orbit the sun and can predict the paths of celestial bodies.

Importantly, all theories can be wrong. They don't have to be correct to be considered theories. They just need to be capable of explaining phenomena and making predictions.

Imagine I have a theory that eating ice cream causes sunburn. I hold this theory because I notice that on days when many people eat ice cream, there are many cases of sunburn, and on days when fewer people eat ice cream, there are fewer cases of sunburn.

My theory seems to explain how sunburn occurs, and it predicts (fairly accurately) when there will be an increase in sunburn cases. But my theory is clearly flawed.

Premise 1 of Churchland’s argument — that folk psychology is a theory — is an important one.

If folk psychology is a theory, then it's possible that it could be wrong. And, just as my theory about the cause of sunburn is wrong, if our commonsense theory of the mind is wrong, it should be eliminated and replaced with a better theory.

So, is Folk Psychology a Theory?

Ordinary people, Churchland argues, are constantly using the concepts of folk psychology to explain and predict other's behaviour.

Imagine you see your friend, Sarah, walking along carrying an umbrella on a sunny morning. Without thinking too much about it, you explain Sarah’s behaviour by thinking that Sarah believes it’s going to rain later today. You’ve used the folk psychology concept belief to explain Sarah’s behaviour.

Later that day, if it does, in fact, rain, you predict Sarah will open her umbrella because of her desire to stay dry. Again, you’ve used a folk psychology concept — this time desire — to predict Sarah’s behaviour.

Folk psychology certainly seems like a theory — we use its concepts to explain and predict.

Premise 2: Folk Psychology is a Bad Theory

So, what’s so bad about folk psychology?

Churchland highlights two main reasons for his low opinion of folk psychology.

1. It does not adequately explain and predict

Imagine two colleagues. Let’s call them Alex and Sam. Alex and Sam have similar lives; they work in the same office, belong to the same network of friends, and enjoy the same extracurricular activities. But Alex and Sam are different in an important way. Sometimes, Alex goes through periods where he rarely leaves his home, speaks little, moves slowly, does not do things he normally enjoys and lies in bed for extended periods.

Churchland argues that folk psychology cannot accurately explain why Alex sometimes behaves like this, nor can it predict when Alex is likely to exhibit these behaviours or how long they might last.

According to Churchland, folk psychology, despite its everyday use, epically fails to explain and predict a great deal of complex mental phenomena. It offers no coherent explanation for mental illnesses like depression, schizophrenia or bipolar disorder. It struggles to explain phenomena like visual illusions, implicit biases, or how memory works. It has no framework for understanding the effects of brain injuries on personality, why we sleep, or how learning transforms us from a baby to an adult.

2. It does not map onto our neuroscientific understanding

To support his second reason for his low opinion of folk psychology, Churchland points out that other scientific fields, such as physics, chemistry, biology, and neuroscience, have each developed into a cohesive theoretical framework. Together, these sciences explain and predict human form and behaviour remarkably accurately. In contrast, folk psychology has remained largely stagnant for centuries and somewhat isolated from the other sciences.

Churchland argues that this stagnation and isolation might be because folk psychological concepts do not clearly map onto what we've been learning in these sciences — especially the neurosciences. And if we can’t incorporate them into our scientific understanding, they should be eliminated.

We already have some evidence of the elimination of folk psychology concepts. Historically, concepts like humors, vapours, hysteria, and animal spirits were part of our common-sense understanding of the mind.

For instance, the theory of four humors (blood, phlegm, yellow bile, and black bile) was once used to explain personality traits and illnesses. Vapours were thought to cause mood swings and anxiety, particularly in women. Hysteria was a catch-all term for various psychological disturbances, again mostly applied to women. Animal spirits were believed to be fluids flowing through nerves, controlling behaviour and emotions. As our scientific understanding has advanced, these concepts have been eliminated from scientific talk and (almost all) everyday language.

With the benefit of hindsight, we might find it easy to see why these concepts were eliminated. What about the folk psychology concepts we commonly use today? Will we eventually eliminate concepts like willpower, character, selfishness, and evil?

Q3: What are the Main Arguments Against Eliminative Materialism?

Some of the main arguments and counter-arguments for and against eliminative materialism draw on the idea of ‘begging the question’. If this term is new to you, or you need a refresher, here's a quick explanation:

• Begging the question is a logical fallacy that occurs when an argument assumes its conclusion is true as part of its reasoning to prove that same conclusion.

• It’s also known as circular reasoning.

• For example, consider the argument that witches are evil, so they must be killed. Therefore, because witches are evil, we should continue to hang them. The premises (witches are evil and evil things should be killed) are used to support the conclusion (witches should be hung). The argument assumes what it's trying to prove.

• In everyday language, begging the question is sometimes mistakenly used to mean raising the question. But this is a misuse of the term in philosophical discussions.

To argue against eliminative materialism, we can challenge its premises, and we can question the soundness of its argument.

Let’s take these arguments in turn:

1. Folk Psychology is Not a Theory

The first argument against eliminative materialism challenges the first premise. It suggests that eliminative materialism is wrong because folk psychology is not a theory.

The critic might argue that we don’t need a theory to tell us about our mental states. Our mental states are experienced directly. The existence of mental states is obvious — in fact, it’s the most obvious of things. I don’t need a theory to tell me that my beliefs, desires, intentions, and pains exist. I know they exist.

To this, Churchland replies that the critic is begging the question. They are making the same mistake that the village people made when claiming that witches should be hung.

To insist that our common-sense understanding of mental states is valid is to beg the question. The premise (I can see that I have mental states) is used to support the conclusion (that I have mental states).

Churchland argues that the conclusions we make about the world are never direct or theory-free. Instead, we always interpret our observations using our existing theories about how the world works. Therefore, the conclusions we draw are shaped by, and limited by, the theories we use to understand our experiences.

So, in the case of witches, the merit of the conclusion is only as good as the theory of witchcraft, which we now recognise as flawed. And in the case of mental states, the merit of the conclusion that mental states exist is only as good as our folk psychological theory, which Churchland argues is similarly flawed and inadequate.

2. Folk Psychology is a Good Theory

The second argument against eliminative materialism accepts that folk psychology is a theory but challenges the second premise.

Sure! claims the critic. ‘Folk psychology might be enhanced by neuroscience. And perhaps some concepts like willpower, character, selfishness, and evil might be eliminated from our vocabulary, but the elimination of ALL mental states is a little over the top, don’t you think?’

Folk psychology, the critic might argue, is actually a pretty useful theory that helps us make fairly accurate predictions about others' behaviours. In fact, we've been using this theory for a very long time, and it has served us well. We don't need to know what goes on in the brain to predict behaviour — folk psychology does a great job.

Perhaps the question of elimination versus reduction of folk psychology will not be answered with a simple either-or. Our future understanding of mental states might involve some elimination but also some reduction. And possibly the introduction of entirely new concepts altogether.

3. Folk Psychology is a contradiction

The third argument against eliminative materialism challenges the logic of eliminative materialism.

If I say I believe that beliefs don't exist, what exactly am I saying?

The claim that the eliminative materialist makes (that beliefs don't exist) requires a belief — in other words, it requires the existence of the very thing it is trying to deny. So, the argument seems logically inconsistent.

But here, again, Churchland claims the critic begs the question.

Churchland claims that the statement is meaningless precisely because the premise assumes the folk psychology concept of belief — which is precisely what eliminative materialism challenges.

Here’s an analogy from Patricia Churchland (Paul Churchland’s wife) that may be helpful:

The anti-vitalist says that there is no such thing as vital spirit. But this claim is self-refuting. The speaker can expect to be taken seriously only if his claim cannot. For if the claim is true, then the speaker does not have vital spirit and must be dead. But if he is dead, then his statement is a meaningless string of noises, devoid of reason and truth. 

In essence, Churchland is arguing that the apparent paradox only arises if we assume that our current folk psychological framework is the only possible way to understand our capabilities.

Churchland’s argument here highlights a common point of confusion for people trying to get their heads around eliminative materialism.

Understandably, when we hear statements like — mental states don’t exist — we naturally think the claim is absolutely absurd!

But the eliminative materialist's claim, while still provocative, doesn't necessarily deny that something is happening in our brains that we currently interpret as experiences. Rather, it suggests that our folk psychological concepts — including our notion of 'experience' are interpreted through the lens of a flawed theory. As our understanding advances, what we think of as experiences might be radically different from our current understanding.

And this is a much more intriguing claim. The intrigue is centred around a fundamental question — when we study consciousness, where should we start?

Should we start with experiences themselves and assume these are true and undeniable? Or do we start with empirical evidence and assume experiences are a type of evidence that can be measured, tested, and analysed? And how do we reconcile these two approaches if they seem to lead to different conclusions?

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Consciousness seems to be a unified, seamless experience.

We perceive the world around us, we think our thoughts, and we feel our emotions. And we do so as part of a seemingly coherent unified stream of awareness. This apparent unity is so fundamental to our experience that we rarely question it.

But there is a problem with this intuitive view of consciousness — the unity of consciousness can break down.

When we think about a conscious experience — let’s say our conscious experience of a blue mug — we assume that our conscious experience of its shape cannot be separated from its colour. The colour is inherently tied to the mug.

But it turns out that we can assign colours to the wrong shapes — even when we have normal, healthy vision.

How could this happen?

We know that different brain areas are specialised to process different types of information. Our brain receives sensory information from the world and, in a way, breaks that information up into its different features — like colour, shape, edges and motion. While some parts of the brain will respond strongly to the blue colour of the mug, others will respond strongly to its edges.

But all the brain's sources and all the brain's cells don't seem to put the blue colour and the mug’s edges back together again — at least not in the way we might expect.

So, why does it feel like it does? Why does our conscious experience seem unified and seamless when our brain doesn't seem to unify its processing into one specific time and place?

This is the binding problem. And it’s a key problem that is frequently discussed in consciousness research.

This week, let’s explore the binding problem by asking three questions:

1. How does the visual system process our visual world?

2. What do people with brain damage tell us about the binding problem? and,

3. How do scientists think the brain solves the problem?

But first, a quick caveat: Accurately explaining how the brain works is an impossible task. In an attempt to explain things clearly, my explanations here will inevitably involve some simplifications and omissions.

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Q1: How Does the Visual System Process Our Visual World?

Let’s start at the beginning. With a blue coffee mug.

Imagine you're at your favourite café. The busy barista has made a variety of coffees, each served in different coloured cups. With a smile, he extends his hand, offering you your order in a deep, blue mug.

Sounds like the perfect start to the day! Doesn’t it!?

It also seems like a simple, everyday moment for your brain to process. But a lot is going on in your head to process this scene.

To state the obvious, all visual information (aka light) comes into your brain through your eyes. From there, neurons extend to an area deep in the brain called the lateral geniculate nucleus (LGN). And then it’s a direct axon step onto the visual cortex — where things get interesting.

The visual cortex is where the brain seems to break down the visual scene into its fundamental components. It is often divided into several distinct areas, for example, V1, V2, V3, V4, and MT. Each region specialises in processing different aspects of vision. For example, V1 (or the primary visual cortex) is primarily involved in detecting basic visual features, with a particular emphasis on lines and edges.

So, if we consider the café scene, V1 would respond strongly to the basic lines and edges you see. Specific groups of neurons in your V1 would detect the edges of the coffee cups, the lines of the counter, and even the contours of the barista's face.

But the café scene doesn’t just have information about edges and lines. Each cup is a different colour and a slightly different shape. Neurons in area V4 respond most strongly to this type of input. So, neurons in V4 would respond preferentially to each cup's colour. The deep blue of your mug would strongly activate one set of neurons, while the bright red of another cup would strongly activate a different group.

To complicate things further, real cafés aren’t static images — in real cafés, baristas hand you coffee in deep, blue mugs (apparently). The area known as MT (or V5) contains neurons that are particularly responsive to motion. So, these cells allow you to track the moving mug so you know how fast the barista is moving the mug towards you.

Do you see the problem?

Your brain is processing all these different aspects of the scene — lines, shapes, colours, and motion in different areas of the visual cortex. But somehow, you don’t see the lines and edges of the coffee mug separately from the mug’s blue colour. And you don’t see the mug’s blue colour separately from the mug’s motion. And when you blink your eyes, the deep blue of your mug isn’t suddenly changed to red. Somehow, you see the lines and edges of the mug, its colour, and its motion as one single, unified mug that is stable over time.

How are you doing that?

We might think that there is someplace in the brain—maybe somewhere towards the front of the brain—that receives all the separate signals from the visual cortex and combines them into one unified visual perception. But no. There is no place like that.

In fact, things seem to get even more separated. From the visual cortex, neurons extend along two distinct pathways:

1. The ‘what’ pathway, which extends downward to the temporal lobe, and

2. The ‘where’ pathway, which extends upwards to the parietal lobe at the top of the brain.

Unsurprisingly, the 'what' pathway is involved in identifying objects. So, it helps us recognise what we see, whether that be faces, places, words, or any other type of object or living thing.

The ‘where’ pathway helps us interact with our world by guiding our actions — our bodies and limbs, as well as our eyes, to where objects are located.

A lot of what we know about the specialisation of different areas of the brain comes from technology such as MRI machines and techniques such as single-cell recordings. But some of the most striking evidence that specific parts of the brain are specialised for different functions comes from studying people with damage to these specific areas.

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Q2: What Can We Learn From Studying People with Brain Damage?

Before we dive into this question, two short caveats:

One

I’ve described the brain areas above as specialised, but it’s important to note that this does not mean they operate in isolation. The brain is highly interconnected, and neurons are continuously influenced by other neurons that are downstream and upstream in the brain.

Two

While studies of brain damage are valuable, we should be careful when we interpret these cases. Damage to the brain often affects multiple areas, not just the area we are interested in, and damage also varies between patients.

It’s also important to remember that while a lack of function might suggest an area is necessary for certain conscious experiences, it doesn't prove that the area alone is sufficient for, or the sole site of, that conscious experience. It just means that the area is likely an essential part of the brain's network that gives us the conscious experience.

Damage to area V4

As mentioned above, colour primarily stimulates neurons in area V4. People who have damage to this area are commonly colour-blind. But this type of colour-blindness is not the same as colour blindness caused by defective photoreceptors in the retina. People with V4 damage can still detect that colours differ, but they have no conscious experience of colour.

So, in the café, they might be able to tell that each cup is a different shade, but they couldn't tell you which cup is blue, red, or any other specific colour. Importantly, they don’t lose their conscious experience of other features like the mug’s shape or its motion.

Damage to Area MT

Neurons in area MT, are primarily responsive to motion. Damage to this area commonly leads to ‘motion blindness’ (akinetopsia). People with this type of brain damage describe moving objects as a series of still snapshots rather than fluid motion. As you can imagine, this would make everyday tasks like pouring a drink or crossing a street extremely challenging.

In the café, people with damage to this area would likely have trouble accurately gauging the speed or direction of the barista's hand as he extends the mug. They might see the mug in one position and, then, suddenly in another without having any conscious experience of the smooth movement between these positions.

But as long as the other areas of their visual cortex are intact, people with motion blindness will continue to experience things like colour and shape normally.

Damage to the ‘what’ pathway

Someone with damage to the ‘what’ pathway will have difficulty identifying and recognising objects.

In the café, people with damage to this pathway might correctly reach for the mug but not be able to name what they are reaching for or describe how to use it.

People with damage in this pathway often have deficits that are specific to categories of objects. For example, damage to one area might result in difficulty recognising places. Damage to a different area might result in difficulty recognising faces — a condition called prosopagnosia.

Some individuals may struggle to bind facial features into a complete face. For instance, they might say, ‘I can see the eyes, nose, and mouth, but these don’t add up to a face.’

In more severe cases, the individual may not even recognise faces as faces, as was the case with Dr. P, a case famously recounted by Oliver Sacks in his book, The Man Who Mistook his Wife for a Hat.

Damage to the ‘where’ pathway

Someone with damage to the ‘where’ pathway often has difficulty accurately reaching for objects. These individuals can clearly perceive and identify objects but struggle to interact with them precisely (this condition is called optic ataxia).

In the café, someone with this condition might see the mug being handed to them and even understand its trajectory of motion, but they will struggle to make the right type of movements required to grasp the mug.

Some people with extensive damage to the 'where' pathway might develop a rare condition known as Balint's syndrome. People with this syndrome have a severely distorted perception of space. They typically can only perceive one object at a time but struggle to describe where that object is in space. While they don't completely lose their sense of 'where', their understanding of how objects relate to space is profoundly impaired. Their concept of space seems limited to the object they are currently seeing. So, instead of seeing a coherent scene, they perceive the world as a series of isolated objects with little context. As you can imagine, this makes navigating the world extremely challenging.

For those with normal, healthy vision, collecting coffee at the café isn’t an experience of isolated patches of colour, disconnected edges, and independent motions. Instead, the experience is one of a unified, coherent, and stable whole. The blue mug, its shape, its motion as the barista moves it, and its location relative to other objects all come together seamlessly.

Yet, given what we know about the specialised nature of visual processing in the brain, we might wonder how our brain brings all these elements together into a coherent whole.

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Q3: How do Scientists Think the Brain Solves the Binding Problem?

Although scientists are still figuring out how the brain solves the binding problem (or whether it solves it at all), they have some clues about what might be going on.

The brain might use spatial position to keep track

When light from the world enters our eyes, that light is projected onto the retinas, similar to how light is projected onto the image sensor (or film) in a camera.

Each area in the visual cortex then acts like a specialised map of what the retina ‘sees’.

For example, neurons next to each other in V1, will respond to locations that are next to each other on the retina. This is true for the other areas in the visual cortex, too. So, we say that areas in the visual cortex are (mostly) retinotopically mapped.

Some cool experiments have been done to show this. For example, in one study, people looked at flashing letters while lying in an MRI scanner. The researchers could see the visual cortex 'light up' in patterns that corresponded to the shape of the letters.

Some scientists think retinotopic mapping might have an important function—it might provide a common frame of reference between areas of the visual cortex, which could be used to solve the binding problem.

The brain might use neural synchrony

Some researchers suggest that for binding to occur, neurons that respond to features of the same object must synchronise their firing. For example, to see the blue mug moving as a coherent object, the neurons in V4 and MT that respond to the mug must fire at the same time or in a coordinated rhythm.

This idea was very popular for a while, but new findings have some scientists questioning whether neural synchronisation is really the answer to the binding problem. It remains an active area of research, so our understanding will likely change as we discover more.

Attention might have something to do with it

In the café, when the barista hands you that deep blue mug, your attention to that moment is likely critical for bringing all those visual features together.

When people are distracted, or their attention is overloaded, they can make what we call ‘conjunction errors’.

To show this effect, a researcher might quickly show you a blue letter H and a red letter T, for example. Then, the researcher might ask you what you saw. If you are able to pay attention to the letters, you will say, I saw a blue letter H and a red letter T.

But, if the researcher were to overload or divert your attention, you are just as likely to say you saw a blue T and a red H. Your brain would get the features right — you would report seeing something blue, something red, the letter H and the letter T, but you might mix up how they combine.

It's as if, without attention, the brain struggles to stick the right features together.

If you're wondering how the brain does this? And what precisely it means for a brain to ‘pay attention’, then you are not alone. Many scientists, myself included, are interested in answering these sorts of questions. While we've made progress, there's still a lot we don’t know.

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I want to take a small moment to thank the lovely folks who have reached out to say hello and joined the conversation here on Substack.

If you'd like to do that, too, you can leave a comment, email me, or send me a direct message. I’d love to hear from you. If reaching out is not your thing, I completely understand. Of course, liking the article and subscribing to the newsletter also help the newsletter grow.

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The brain is a computer… or so they say.

During my undergraduate studies, I often heard the mind explained as the “software” that runs on the “hardware” of the brain.

But is this true?

Increasingly, researchers are starting to question whether the computer metaphor is appropriate. In fact, many argue it's not just wrong, but it’s causing problems. It’s getting in the way of understanding how the brain actually works.

But the brain-is-a-computer metaphor remains standard in neuroscience and artificial intelligence. And, the reasoning goes, if the mind really is ‘software’ that runs on the brain's neural ‘hardware’ — then it raises a provocative possibility that if minds are like computer software, complex computer software (like LLMs) might be like minds. Computers might (at least someday) be conscious.

When we hear talk like this, we might be inclined to point out the many ways that brains are, in fact, not like digital computers.

But while it is true that the list of differences between digital computers and brains is long, I suspect simply listing these differences is unlikely to convince anyone either for or against the possibility of conscious AI.

The question we really want to ask is:

Are the differences between brains and digital computers the kind of differences that truly matter when it comes to consciousness?

While the computational functionalist might lean towards answering, no — the biological naturalist would lean towards a yes!

Let’s find out why the biological naturalist thinks AI might never be conscious.

This week, we’re asking three questions:

1. Is the mind “software” that runs on the “hardware” of the brain?

2. Could biology be the difference that makes a difference? and,

3. What if we designed digital computers to function more like brains?

But first… a difference between philosophy and science

In this article, I will refer to a prominent scientific theory of consciousness. Before doing so, I want to highlight an important distinction between scientific theories of consciousness and philosophical ones.

In philosophy, much of the study of consciousness comes under the larger field called metaphysics. Metaphysics is interested in questions about the fundamental nature of reality. So, philosophers interested in metaphysics are interested in the broad question about what exists? When it comes to consciousness, philosophers might ask questions like, What is consciousness made of? or What are the essential properties that distinguish a conscious experience from an unconscious one?

Scientists, on the other hand, tend to have a different focus. Instead of asking what consciousness is made of, scientists tend to ask questions like, How does consciousness work? or What is the function of consciousness?

This difference in approach can sometimes lead to frustration. We usually want to define what we are studying in the what-it-is-made-of sense before addressing questions about how it works.

Scientists working on consciousness often respond to this frustration in one of two ways. They either say, let’s focus on the scientific questions and leave the philosophical questions to the philosophers. Or (if they are feeling a little braver), they might suggest that scientific discoveries about the function of consciousness could provide important clues and set essential boundaries for philosophical theories.

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Q1: Is the mind ‘software’ that runs on the ‘hardware’ of the brain?

A persistent idea in computer science is the separation of software and hardware.

Software is the code—the programs that run on a computer. You can think of software as the functions a computer performs. Hardware is a computer's physical components, such as its processor, memory, and hard drive.

This separation has been critical to the development of computer science. Separating hardware from software allows software to be developed, copied, and run on many different types of hardware without too much concern about how the hardware is made. It also means those who develop the software can distribute it worldwide and still be confident that it will run the same way and produce the same results, no matter how many copies are made. And, it allows the same software to be run on multiple hardware simultaneously, which means processing massive data sets is possible.

Brains don’t work like this.

The brain's hardware (e.g. its neurons and neurotransmitters) cannot be easily separated from the functions it performs.

Every time our brain does anything — we solve a complex problem, learn a new skill, or process sensory information — our brain physically changes. Neurotransmitters are released into synapses that bind to receptors. New synapses are formed, or existing ones are pruned and reorganised. Even neurons die, and (as discovered recently) new ones are generated, even throughout adulthood. These physical changes are thought to be responsible for our experiences.

Even simple physical changes in the brain can cause large changes in perceptions, thoughts, and feelings.

Anyone who has taken a psychedelic substance can confirm that seemingly minor physical changes can have dramatic effects on our conscious experiences.

Consider psilocybin (the active compound in magic mushrooms). Psilocybin is metabolised into psilocin, which just so happens to be structurally very similar to one of the brain's key neurotransmitters — serotonin.

To oversimplify it, when psilocin gets into the synapse of a neuron with serotonin receptors, it can do what serotonin would normally do but with amplified effects.

The result? Profound changes in perception, cognition, and emotional state that we recognise as a psychedelic experience. This chemical change leads to a radically different conscious experience.

Effects like the ones seen with psychedelic substances suggest that if there is a line to be made between the brain's hardware and software, the line is a blurry one.

This leads to an important distinction between brains and computers.

In computers, because software can be copied and executed on different hardware, a computer’s software (the functions it performs) is independent of its hardware. Software does not die if the hardware fails. Software is immortal.

But this is not true for brains. If the brain’s hardware dies, its functions die, too. Unlike computers, where software can be transferred or backed up, the brain's functions are inextricably tied to its physical structure. The brain’s functions are mortal.

Could mortality be the key? Is there something about being mortal that is fundamental for consciousness?

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Q2: Could Biology be the Difference that Makes a Difference?

To address this question, I'll draw on ideas presented in two key articles. The first is a recent paper by Alexander Ororbia and Karl Friston, which explores the distinction between mortal and immortal computation. The second is an article by Anil Seth, where he advances his argument that consciousness might be fundamentally dependent on biological processes.

It's important to note that both of these articles are pre-prints, which means they are early-stage research papers that have not yet undergone the rigorous peer review process. So, while the ideas presented here are intriguing, they should be considered preliminary. These concepts may evolve or change significantly as they face scrutiny from other experts and are tested against experimental evidence.

Let's begin with Ororbia and Friston's ideas. In their paper, they make a simple statement with important implications. They highlight that the key to a living system’s survival is that system’s ability to maintain a clear boundary between itself and the external world.

This will be an important concept, so let’s unpack.

Consider a simple biological system. It is vital that this simple system maintains a boundary between itself and its surroundings.

A clear boundary between self and the outside world helps the biological system survive in a few key ways. It helps the system identify what it needs to protect from what might be dangerous threats or important resources. It also allows the system to regulate what enters itself and what exits. And it provides a way to clearly distinguish between the system's own status and the status of the external world.

Digital computers don’t need to do this. Immortal computational systems function without concern for their own existence, so they don’t need to know where they begin and end. But because the functions of a biological system depend on the integrity of its physical ‘hardware’, to continue to perform its functions, the system must maintain its physical boundary to ensure its survival.

According to Anil Seth, this fundamental difference between mortal and immortal systems is critical for consciousness. He thinks this difference might explain why replicating consciousness in artificial systems may be challenging.

Let’s unpack Seth’s claims.

A biological system changes — it moves in its world, requires resources, and needs maintenance. So, its internal status is in constant flux. But the biological system is not the only thing that changes. The external world changes, too. To survive, the biological system must monitor both its internal status and the status of its external world.

For example, consider a lion hunting in the savanna. It must constantly monitor its internal state—its hunger level, energy reserves, and how it is physically positioned in the world. At the same time, it needs to track changes in its environment—the movement of potential prey, the presence of competitors or threats, and shifts in weather conditions. The lion's survival depends on its ability to monitor these internal and external factors.

Seth explains that we monitor our internal and external worlds by generating predictive models. The predictive process that Seth describes aligns with a prominent theory of how the brain works. So, let’s briefly review that theory.

The Predictive Processing Theory

The Predictive Processing Theory, developed by neuroscientists like Karl Friston and popularised by philosophers such as Andy Clark, offers an explanation for how our brains process information.

The theory proposes that the brain is essentially a prediction machine. According to this view, our brains constantly generate hypotheses about the world.

Our brains aren't like passive radio receivers. We don’t simply take in whatever signals the world sends our way and broadcast them as an accurate internal representation of those signals. Instead, we are constantly predicting ourselves and our world. We use the signals from our bodies and the world to update those predictions.

This can sound a bit abstract, so let's consider an example.

You might be a lover of classical music (or perhaps the bagpipes are more your thing). Whatever your go-to tune, when you listen to your favourite song, your experience is not just about the notes you hear at any precise moment. It’s also about what you have just heard and what your brain predicts you will hear in the near future.

We are constantly making predictions. These predictions are not exact. They are just approximations — our brain’s best guess — based on prior experiences and the current context. We use these best guesses to navigate our world. When we hear our favourite song, see a familiar face, or navigate a crowded room, we're experiencing our brain's best guess about the causes of the incoming signals.

If your favourite song unexpectedly stops or the melody changes, you would have made what scientists like to call a prediction error. But we usually just call it a surprise. Any differences between what we predict and what actually happens are used as feedback to update and refine our future predictions.

While the Predictive Processing theory doesn't make strong claims about consciousness, some researchers, like Anil Seth, propose that consciousness is closely related to the predictive process. Seth’s ideas also align with biological naturalism — the view that consciousness is biological — a view most notably associated with John Searle. Building on these foundations, Seth suggests that the things we are conscious of are given to us by the brain’s best guesses. In this way, prediction might be the primary function of consciousness.

As we explored above, prediction is fundamental to the survival of any mortal system. Failure to do so usually means death. So, prediction and survival are closely linked in biology.

But what about computers?

The relationship between prediction and survival, which we see in biological systems, doesn't hold true for digital computers.

While computers can perform complex functions and even run sophisticated predictive models like brains do, they don't maintain themselves in the same way living organisms do. If a computer fails to perform its predictive functions correctly, it doesn't risk death in any meaningful sense. Because the software running the prediction model is entirely separate from the hardware it runs on, a software’s existence doesn't depend on the accuracy of its predictions or computations.

Some who are convinced by Seth’s logic might feel a sense of relief. The difference between mortal and immortal computation would make the possibility of conscious AI unlikely. Following this reasoning, if the function of consciousness in mortal systems is to generate predictions that enhance survival, then the absence of the survival-driven need in computers is a significant barrier to artificial consciousness.

But even if Seth’s claims convince us, we may not want to breathe a sigh of relief just yet.

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Q3: What if we designed digital computers to function more like brains?

Geoffrey Hinton — often dubbed the grandfather of artificial intelligence — recently proposed creating mortal computers.

He suggests that while the separation between software and hardware provides many benefits, it may limit our ability to create more efficient and potentially more intelligent AI systems.

He proposes the development of mortal computing in which hardware morphs as the computer learns—similar to how a brain morphs when it learns. And like a brain, the procedures the computer discovers would only work for that particular hardware, so the functions would be mortal—they would die if the hardware fails.

Hinton's main motivation for such a system is its significant energy savings. Mortal computers will likely be a little less accurate but far more energy-efficient than immortal ones.

If Anil Seth is correct and properties of life, such as mortality, are necessary for consciousness, could these mortal computational systems be conscious?

It’s important to note that Seth does not make the strong claim that properties of life, such as mortality, guarantee a system will be conscious, only that properties of life may be necessary for consciousness.

With that caveat in mind, we may still wonder whether mortal computing systems might behave in similar ways to biologically mortal organisms. Would they have similar biological drives to maintain a clear boundary between themselves and the outside world? Would they generate predictive models of themselves and their environment? And if they did, would this mean these systems were conscious? Or would they still lack something important?

It's worth noting that while the Predictive Processing theory has gained significant traction in neuroscience, not everyone is convinced by its claims and it is certainly not the only view about how the brain works.

If you would like to learn more about the possibility of mortal computers, I recommend watching the following lecture by Geoffrey Hinton:

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Functionalism is currently the most popular theory of consciousness. It's the idea that consciousness — all our thoughts, feelings, and beliefs are not defined by what they are made of but by what they do. This theory is also behind the idea that AI might be conscious (now or sometime in the future) because, given the right type of machine, it could replicate the functional states of a human mind. But despite its popularity, not everyone is convinced by the functionalist claims.

So, what's the issue with functionalism?

This is Part 5 of our series on physicalism, the theory that the physical world can fully explain consciousness. This week we’re continuing our exploration of functionalism. Last week we set up three questions and addressed the first two:

1. What is functionalism? and,

2. Why might someone believe in functionalism?

You can find last week’s article here:

This week we’re asking the third question.

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What are the Main Arguments Against Functionalism?

There are several arguments against functionalism. Let’s review five popular ones.

It's important to note that there are many different types of functionalism. And the different types of functionalism are often the evolved response to the following arguments. So, not all of these arguments will apply equally to every type.

1. The Inverted Qualia Problem

Qualia refers to the qualitative and intrinsic aspects of our mental states. It's the what-it-is-like to see the redness of a ripe tomato, feel the sharpness of a bee sting on the tender side of your foot, taste the rich, nutty sweetness of pistachio gelato, or smell the crisp, salty ocean air after a storm.

Critics claim that functionalism simply cannot account for these subjective experiences. Even if we could fully describe all the functional and causal roles of a mental state — that type of explanation will always be missing something essential — the subjective feeling of the experience itself. Qualia, the critic claims, cannot be reduced to mere functional roles or computational states.

Philosophers have developed various thought experiments to illustrate this problem. The inverted spectrum argument is one such thought experiment.

The Inverted Spectrum

I have outlined the inverted spectrum thought experiment in my article Is Consciousness Computational?

Here’s what I wrote there:

Imagine two people. Let's call them Alice and Bob. Externally, they both seem to react to colours in the same way. They stop at red lights, go at green lights, and so on. However, internally, their experiences of colours are different. What Alice experiences as red, Bob experiences as green, and vice versa. Their colour experiences are inverted relative to each other.

According to functionalism, if two beings (like Alice and Bob) have the same functional responses to stimuli, they should have the same internal experiences. But the inverted spectrum hypothesis suggests that it's possible for two people to have the same functional responses (e.g., both stopping at red lights) while having different internal experiences (seeing different colours).

This scenario with Alice and Bob suggests that functional roles alone cannot capture the full nature of conscious experience. Critics suggest that the inverted spectrum thought experiment poses a significant challenge to functionalism.

In a future article, I’ll discuss the functionalist’s counter-arguments to these claims. In the meantime, you might find the article Is Consciousness Computational? interesting. There, I outline one counter-argument to the inverted spectrum thought experiment.

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2. The Absent Qualia Problem

Philosophers love thought experiments. Thought experiments ask us to imagine a situation that is beyond our experiences. Two of the best-known thought experiments that are arguments against functionalism involve China — The Chinese Room by John Searle and The China Brain by Ned Block (also known as the Chinese Nation). Both thought experiments make similar arguments.

Searle’s Chinese Room thought experiment is probably the most popular. I wrote a little about it in my article — If AI Were Conscious, How Would We Know? I have more to say about this thought experiment, and I’ll do that in a future post, but I want to focus on Block’s argument in this article.

The China Brain

In 1978, Ned Block proposed his thought experiment as part of his famous paper, Troubles with Functionalism.

Block writes:

Imagine a body externally like a human body, say yours, but internally quite different. The neurons from sensory organs are connected to a bank of lights in a hollow cavity in the head…. Inside the cavity resides a group of little men. Each has a very simple task...

The idea of little men inside the head refers to homunculi, a term derived from Latin meaning little men or miniature humans.

Block continues:

How many homunculi are required? Perhaps a billion are enough; after all, there are only about a billion neurons in the brain.

China's population was around 1 billion people in 1978, so Block chose China for his thought experiment. However, Block significantly underestimated the number of neurons in the brain. In 1978, the estimated number of neurons in the brain was actually 100 billion (we now estimate it to be about 86 billion for adults).

Block continues:

Suppose we convert the government of China to functionalism… We provide each of the billion people in China… with a specially designed two-way radio that connects them in the appropriate way to other persons and to the artificial body mentioned…

Block continues by imagining that the entire population of China is organised to simulate the functional roles of neurons in a brain — let’s say your brain.

Each person, equipped with a special radio, acts as a single neuron, receiving and transmitting signals according to simple rules. This massive system is connected to the artificial body.

The crucial question Block poses is whether this system, which perfectly replicates the functional organisation of your brain, would possess consciousness or subjective experiences as you do.

Block proposes this thought experiment because he is convinced most people will say — obviously, it’s not conscious. And if we believe that this "China Brain" lacks genuine consciousness despite being functionally identical to your brain, it suggests there's something more to consciousness than the functionalist account allows.

Functionalist counterarguments to this absent-qualia problem typically follow two paths: either they claim that this "China Brain" would indeed be conscious, or they challenge the conceivability of the thought experiment itself. This second approach argues that, as described, it is simply not physically possible for such a system to replicate the functional organisation of a human brain and, therefore, would not function like a human brain.

3. The Too Liberal Problem

You may remember from a few weeks ago that the mind-brain identity theory faces criticism for being too conservative or carbon chauvinistic — it doesn't allow for the possibility of consciousness in non-biological systems.

Last week, we discussed multiple realisability, an aspect of functionalism often seen as an advantage over the identity theory. This feature allows consciousness to exist in various physical substrates, not just biological brains.

However, while multiple realisability is generally considered a strength of functionalism, some argue it goes too far in the opposite direction. Critics claim that functionalism is too permissive, potentially attributing consciousness to systems we wouldn't want to consider conscious. In other words, if identity theory was too conservative, functionalism might be too liberal.

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4. The Homunculus Fallacy Problem

In Part 1 of the series on The Five Most Controversial Ideas in the Study of Consciousness, we discussed the homunculus fallacy.

Here’s a recap and how this fallacy might relate to functionalism:

Because functionalism explains mental states in terms of their functional roles, some critics have argued that this explanation implicitly assumes some sort of inner "processor,” “overseer,” or "interpreter" of these functional states. They think that for functional states to have meaning, some internal mechanism must read or interpret them.

This has some asking: how do we explain the conscious experiences of this inner interpreter?

If we explain the inner interpreter's consciousness with another set of functional relationships interacting with other mental states, we'd need another interpreter to interpret those interactions. This process could continue indefinitely, creating an infinite series of "homunculi" or inner interpreters.

Ned Block's China Brain thought experiment illustrates this problem. In his scenario, the functional organisation of a brain is simulated by the entire population of China. The question arises: where does consciousness emerge in this system? Some might suggest that consciousness only appears when the system is connected to the artificial body, implying the need for a central "interpreter" — or a theatre of sorts — where the input from all 1 billion people comes together as one experience for the interpreter to experience. But this interpretation is the Homunculus Fallacy in fine form.

It's worth noting that not all forms of functionalism fall prey to this critique. For instance, Daniel Dennett offers a version of functionalism in his book Consciousness Explained that attempts to address these concerns. Dennett's approach avoids positing a central interpreter, instead describing the system as a hierarchical structure where lower levels of the system become less and less functionally organised until we approach the mechanistic level of the neuron (or groups of neurons).

5. The Function Needs Form Problem

Functionalism often compares brains to computers. The common claim is that the mind is software running on the hardware of the brain.

Not all versions of functionalism strictly adhere to the computer analogy, but the recent popularity of AI has many leaning towards this view. The claim is that just as artificial neural networks are a complex computational process, so are real neural networks. In recent years, computational functionalism has become one of the more prominent theories of consciousness.

But not everyone is convinced by this analogy—indeed, many disdain such a view.

Neuroscientist Anil Seth questions the assumptions behind the brain-is-a-computer analogy in his recent article Conscious Artificial Intelligence and Biological Naturalism.

Seth explains that in traditional computing, software is designed to work the same way regardless of what specific computer it's running on. We can take software, copy it, and execute it on different hardware. This is true even for adaptive software, like machine learning algorithms. The entire system relies on the separation between software and hardware.

According to Alexander Ororbia and Karl Friston, software like this is immortal — it can theoretically exist forever, independent of any particular hardware.

Seth argues that the brain's very structure challenges the computer analogy. Unlike computers, which clearly distinguish hardware and software, brains show no such separation between wetware and mindware. In the brain, the neural connections (wetware) are constantly changing. And these physical changes are thought to be responsible for our experiences (mindware). When it comes to brains, there may be no way to separate their form from their function.

Based on work by Alexander Ororbia and Karl Friston, Seth suggests that if the brain is doing computations, they must be mortal — once the wetware (brain) changes or fails, the mindware (specific functions) will cease to exist.

This inseparability of form and function in the brain challenges a key tenet of functionalism: the multiple realisability thesis. If Seth is correct, and the brain's wetware is inextricably linked to its mindware, it suggests that consciousness might be more tightly bound to its biological substrate than functionalism assumes. This would imply that creating conscious AI using non-biological hardware and immortal software could be more challenging or even impossible if consciousness depends on the specific properties of biological neural networks.

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The Sum Up

Functionalism, despite its popularity in explaining consciousness, faces several challenges.

• The inverted qualia problem questions whether functional roles can truly capture subjective experiences,

• while the absent qualia argument, exemplified by the China Brain thought experiment, suggests that functional equivalence might not guarantee consciousness.

• Critics also worry that functionalism might be too permissive, potentially attributing consciousness to unlikely systems.

• The homunculus fallacy problem concerns an implicit need for an inner interpreter, leading to a potentially infinite regress.

• Finally, the function-needs-form argument challenges the brain-computer analogy, suggesting that consciousness might be inseparable from the brain's physical structure.

These critiques don't invalidate functionalism entirely, but they do highlight significant areas where the theory is most likely to be challenged. The debate over functionalism's legitimacy as a solid theory of consciousness remains far from settled.

We will leave functionalism for now and continue exploring other physicalist views. Next in the series is Eliminative Materialism.

Thank you.

I want to take a small moment to thank the lovely folks who have reached out to say hello and joined the conversation here on Substack.

If you'd like to do that, too, you can leave a comment, email me, or send me a direct message. I’d love to hear from you. If reaching out is not your thing, I completely understand. Of course, liking the article and subscribing to the newsletter also help the newsletter grow.

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• You can become a paid subscriber

• or you can support my coffee addiction through the “buy me a coffee” platform.

Buy me a Coffee?

I want to personally thank those of you who have decided to financially support my work. Your support means the world to me. It's supporters like you who make my work possible. So thank you.

Welcome to Part 4 of our series on physicalism, the theory that the physical world can fully explain consciousness. This week we’re exploring functionalism — currently the most popular theory in the philosophy of mind and in scientific fields that study consciousness — like cognitive neuroscience. But just because a theory is popular doesn’t make it true. So, let’s explore the merits of the functionalist’s claims.

As we have done with other consciousness theories, we’ll ask three questions:

1. What is functionalism?

2. Why might someone believe in functionalism? and,

3. What are the main arguments against functionalism?

Unlike other consciousness theory articles, functionalism will be addressed in two parts. Let’s address the first two questions this week and leave question 3 for next week.

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But before we jump into the questions, let’s do a little recap.

Way back in the series on The Five Most Controversial Ideas in the Study of Consciousness, we started with some non-physicalist views. We looked at Descartes' substance dualism and epiphenomenalism. Both of these theories claim that when it comes to consciousness, there are two things: the physical brain and the mind, which is not made of physical things.

In this series on physicalism, we will review some of the main alternatives to these non-physicalist views. So far, we’ve explored one of these theories — the mind-brain identity theory (aka reductive materialism), which is the view that the mind is the brain. In the article on the identity theory, we spent some time discussing what might be meant by the word ‘is’ in their claim that the mind is the brain.

This article is going to draw heavily on what we discussed in the identity theory article, so if you need a recap, here’s the link:

Great! Let’s get into the questions.

Q1: What is Functionalism?

Functionalism emerged as a response to two earlier theories of mind: the identity theory (which we explored in Part 3) and behaviourism (which we haven’t discussed yet). While functionalism incorporates elements from both of these earlier theories, it also significantly departs from them.

There are many different types of functionalism. Not all of them agree with each other. But what is agreed is that when it comes to defining mental states, what matters is the role or job of the mental state, not what it is made of.

Like the identity theory, functionalism is a physicalist theory. But the functionalists think consciousness is a different type of physical kind than the identity theorists claim.

For the identity theory, consciousness is the brain kind. But for functionalists, consciousness is — the functional kind.

So, what is a functional kind?

Some things are defined by what they do — not by what they are made of.

Functional kinds are the kinds of things that are defined by their inputs and outputs. More specifically, the kinds of things where the inputs are causes and the outputs are effects.

For example, a toaster is a functional kind. The function of a toaster is to toast bread — to input bread and, after a short time, to output toast. The toast is the output effects of the function of the toaster. And we define a toaster by the function it performs. If a toaster does the job of toasting — it’s a toaster. It doesn’t matter what a toaster is made of or what it looks like; as long as it toasts, we define it as a toaster.

Not all things are functional kinds. For example, we probably wouldn't define water solely by its function. We tend to define water by what it is made of (H₂O) or by its physical properties, such as being a clear, odourless, tasteless liquid at room temperature that freezes at 0°C and boils at 100°C at standard atmospheric pressure. While water certainly has many functions (like hydrating living organisms or eroding landscapes), these functions don't define what water is in the same way that toasting defines a toaster.

Poison is another example of a functional kind. The function of poison is to cause harm or death when ingested, inhaled, or absorbed. We define poison by this function, not by its chemical composition or physical properties.

It is true that when we define specific poisons, we define the chemical composition of that specific poisonous substance. But when we define the concept of poison itself, we define it by the function it performs — input a substance and output the harmful effects. This definition of poison holds regardless of the specific chemical makeup of a poison. What matters is the function — if a substance poisons, it's a poison.

We might wonder about other examples we’ve discussed so far. Is a table a functional kind? What about a hat? Or a ship?

If something performs the function of a table — it holds objects at some height above the ground — we call it a table. And if something performs the function of a hat — we can wear it on our head to shield our face from the sun — we call it a hat.

You can probably see where we are going here.

Functionalism claims that mental states are a functional kind. We define consciousness by the functions that are performed — input a cause and output an effect. The definition of a conscious mental state holds regardless of the physical substrates that implement these functions. It doesn't matter what the substrate is made of. As long as it performs the right type of function, it's conscious. Just as a toaster is defined by its function of toasting, regardless of its physical composition, conscious mental states are defined by their functions, regardless of whether they are implemented in biological neurons, silicon chips, or any other medium capable of performing these functions.

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Q2: Why might someone believe in Functionalism?

When something can be implemented in many different systems, it is said to be multiply realisable.

Multiply realisability is a key principle in functionalism because functional kinds are multiply realisable.

Tables, toasters, hats, and poison are multiply realisable — they can be made from many different things. As long as they continue to perform the function that defines them, they don’t lose their definition.

This is not true for brains. Brains are defined by what they are made of — by their biological structure. So, when the identity theory claims that the mind is the brain, they are making a claim about what mental states are made of — mental states are brain states. And, according to the identity theory, because mental states are brain states, mental states must be made out of brain stuff — they are not multiply realisable.

This brings us to the key question that defines the debate between the identity theorists and the functionalists:

Are mental states multiply realisable?

If mental states are only implemented in one type of system, we might suggest that the evidence favours the identity theory. But, if mental states can be implemented in many different systems, the functionalists might have the stronger claim.

Let’s review the evidence:

Brains are diverse

Learning requires the strengthening and weakening of neural connections. Your brain would have formed connections when you learned language as a child. But the connections that formed in your brain will almost certainly be different from the connections formed in mine. Even if we both learned the same language.

Imagine Sally and Jose. Sally and Jose both learned English as a child. Because brains develop differently, they do not have the same wiring. But here’s the thing — it doesn’t matter. Sally and Jose can both understand and speak English. It doesn’t matter which neurons fire; it's about getting the job done. And despite how diverse their brains are — they still achieve the same results — they understand and speak the same language.

Brains Across Species

Last week we discussed the octopus. These creatures are very different from humans, with a common ancestor roughly 550 million years ago. Octopus brains are very different from ours — most of their neurons aren't even in their central brain but in their arms!

Yet, despite these differences, octopuses display some remarkably similar functions to humans. They can solve complex problems, use tools, and even show signs of play behaviour. They're capable of learning, remembering, and adapting to new situations — much like we do.

It doesn't matter that an octopus brain is wildly different from a human brain. What matters is that both can perform similar functions — both can learn, problem-solve, and adapt. The physical stuff doesn’t matter — it’s about getting the job done.

Brains Change

Our brains have an incredible capacity to adapt and reorganise themselves, a property known as neuroplasticity. Studies of blind individuals, particularly those who lost their sight at a young age, provide a fascinating example of this.

In people with normal vision, the visual cortex primarily processes visual information from the eyes. However, in individuals who are blind, particularly those who have been blind since early childhood, the visual cortex doesn’t sit idly. Instead, it adapts to serve other functions. It gets repurposed for other sensory processing. For instance, when blind individuals read Braille, their visual cortex is often highly active — it’s not processing visual information — it’s processing tactile information from the fingertips.

Studies have shown that blind people often have enhanced auditory abilities, and their visual cortex shows increased activity when listening to sounds or speech. The brain has essentially rewired itself, using the available neural real estate to enhance other senses.

This adaptability isn't about preserving specific brain structures or connections. What matters is that the brain finds a way to perform necessary functions, even if it means completely repurposing areas typically used for something else. To perform the function of reading braille, it doesn't matter whether it's the visual cortex doing the work or some other part of the brain; what matters is that the reader can effectively get information from and interact with their environment. It's not about which specific neurons are doing the job but about getting the job done.

Brains can deal with Artificial Aids

Our brains have a remarkable ability to adapt to and integrate artificial inputs as long as they serve the same function as natural ones. A prime example is the cochlear implant — a device that has revolutionised the treatment of severe hearing loss.

Cochlear implants don't work like normal hearing. They bypass damaged parts of the ear and directly stimulate the auditory nerve with electrical signals. These signals are very different from what the brain normally receives from a functioning ear. Yet, with time and practice, the brain learns to interpret these artificial signals as sound.

What's fascinating is that it doesn't matter to the brain that the input comes from an electronic device rather than natural hair cells in the cochlea. The brain adapts to process this new input type, ultimately achieving the same function: hearing. People with cochlear implants can understand speech, enjoy music, and perceive environmental sounds, even though the signals their brains are receiving are fundamentally different from those in natural hearing.

This adaptability extends to other sensory substitution devices as well. For instance, some devices convert visual information into tactile sensations, allowing blind individuals to "see" with their skin. Again, the brain adapts to interpret these unusual inputs meaningfully.

The Sum Up (so far)

The evidence from diverse brain structures, cross-species comparisons, neuroplasticity, and adaptation to artificial aids suggests that mental states are multiply realisable — at least in brains. The examples above suggest that what matters is the function being performed, not the specific neural structure.

BUT! Let’s not jump on the functionalist bandwagon before considering the arguments against functionalism. We'll explore these arguments in detail next week.

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For those interested in doing more in-depth reading on functionalism, these are the main resources I used for this article (if you are new to functionalism, I recommend the article by Adam Bradley):

• The Nature of Mental States, by Hilary Putnam

• Troubles with Functionalism, by Ned Block

• The Causal Theory of the Mind, by D.M. Armstrong

• Mind, Language, and Reality, by Hilary Putnam

• A Primer on Multiple Realizability and Functionalism, by Adam Bradley

Thank you.

I want to take a small moment to thank the lovely folks who have reached out to say hello and joined the conversation here on Substack.

If you'd like to do that, too, you can leave a comment, email me, or send me a direct message. I’d love to hear from you. If reaching out is not your thing, I completely understand. Of course, liking the article and subscribing to the newsletter also help the newsletter grow.

If you would like to support my work in more tangible ways, you do that in two ways:

• You can become a paid subscriber

• or you can support my coffee addiction through the “buy me a coffee” platform.

Buy me a Coffee?

I want to personally thank those of you who have decided to financially support my work. Your support means the world to me. It's supporters like you who make my work possible. So thank you.

Welcome to Part 3 of our series on physicalism, the theory that the physical world can fully explain consciousness. This week let’s examine reductive materialism (often called the identity theory).

This article will draw on concepts we covered in Parts 1 and 2. So, if you haven’t done so already, you may want to read Parts 1 and 2 before reading this article, especially if you are new to physicalism theories.

Part 1

Part 2

This week we’re asking four questions:

1. What is the identity theory of the mind?

2. Why might someone believe in the identity theory?

3. What is the main objection to the identity theory?

4. What is the counter-argument to this objection?

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Q1. What is the Identity Theory of the Mind?

In its simplest form, the identity theory of the mind is the idea that the mind is the brain.

In other words, every experience, such as feeling happy or thinking about a problem, is fundamentally one and the same as a particular pattern of neuronal activity or brain state.

The identity theory adopts a reductionist approach, meaning it claims that the mind (or consciousness) is one and the same thing as the neural processes that give rise to it. When making this claim, the identity theorist often draws on analogies found in other areas of science. For example, they might liken consciousness to light or temperature, claiming that just as light is simply electromagnetic waves and temperature is simply the kinetic energy of molecules, specific conscious states are simply specific brain states. Just as light doesn’t seem like electromagnetic waves, and temperature doesn't seem like the kinetic energy of molecules, consciousness doesn’t seem like neural processes — but that’s what it is.

Proponents of the identity theory argue that as neuroscience, particularly cognitive neuroscience, advances, it will eventually uncover the precise brain states and processes that correspond to specific experiences. This one-to-one correspondence between the mental and the physical would effectively dissolve the perceived divide between the mind and brain. The mind is simply the brain.

Notice how the identity theory claims that the brain is the only possible basis for consciousness. If the mind is the brain, there is no room for artificial intelligence (AI) to ever be conscious. Some may find this view narrow-minded. Indeed, the identity theory has been dubbed the carbon chauvinist theory. But just because a theory might seem narrow-minded doesn’t mean it isn’t true. There are several reasons why someone might advocate for the identity theory.

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Q2. Why might someone believe in the identity theory?

There are three main arguments often raised in support of the identity theory:

Humans are physical beings

Our bodies, including our brains, are composed of matter and energy that operate according to the laws of physics. Since we are part of the physical world, some argue that it follows that our behaviour, cognition, and conscious experiences are best understood as physical processes, too.

Evolutionary explanation

Over billions of years, evolutionary forces have gradually shaped our brains to better take in our environment and coordinate our behaviour to ensure survival and reproduction. It is the product of an extended evolutionary process driven by physical causes. From this perspective, the identity theorist argues that consciousness is no different. Consciousness is simply an evolutionary adaptation. We have conscious experiences, simply because it is favourable for survival and reproduction.

The neural dependence of mental phenomena

There is an abundance of evidence from the neurosciences that our thoughts, emotions, perceptions, and sensations depend on the brain’s structure and activity. We know that if we damage or alter specific brain regions, we will see corresponding changes to specific behaviours and mental abilities. For instance, damage to the hippocampus, a region deep in the brain, can severely impair the ability to form new memories, while injuries to the visual cortex at the back of the brain can cause blindness or visual impairments.

But we don’t have to damage the brain to see the connection between the brain and the mind — modern neuroimaging techniques, like functional MRI scans, have been correlating particular conscious states with specific brain patterns for many years.

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Q3. What is the main objection to the identity theory?

One argument against the identity theory stems from the first-person experience of consciousness and subjective awareness. When we introspect and examine our own thoughts and feelings, they can seem fundamentally different from purely physical processes. We’ll address this argument a little later on. For now I want to focus on the main argument against the identity theory of mind.

The Category Error Argument and Leibniz's Law

The most popular critique against the identity theory of mind is the argument that it commits a category error by conflating mental and physical properties. According to this objection, consciousness belongs to a fundamentally different ontological category than brain states and brain processes.

This argument draws on Leibniz's Law, which states that if two things (x and y) are absolutely identical, then any property that applies to x must also apply to y, and vice versa. For example, we might claim that the morning star is the evening star. According to Leibniz's Law, any property that applies to the morning star must also apply to the evening star. Because both the morning star and the evening star refer to the planet Venus, we can conclude that they are, in fact, the same celestial body, just observed at different times of day.

Critics of the identity theory argue that there are properties that apply to consciousness that do not apply to brain states and processes. For example, consciousness is often described as the intrinsic subjective first-person experience, while brain states and processes are observable from a third-person viewpoint. Therefore, according to Leibniz’s Law, the mind (or consciousness) cannot be the brain.

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Q4. What is the counter-argument to this objection?

Many view Leibniz's Law as the strongest argument against the identity theory. However, the philosopher U.T. Place offers a counterargument that is worth reviewing.

In his seminal paper, Is Consciousness a Brain Process?, Place suggests that logical arguments, like Leibniz’s Law, fundamentally misunderstand the identity theory’s claim.

Before we get into Place's counterargument, we need to discuss the word 'is'.

Place explains that we can use the word is in different ways. And in the sentence the mind is the brain, the meaning of the word 'is' can be ambiguous.

The is of definition.

We can use ‘is’ in the definitional sense. This is usually in the form of ‘noun is noun’. For example, we might say that a square is an equilateral rectangle or red is a colour. In this case, if our statement is true, it will be necessarily true by definition. A statement — a square is an equilateral rectangle — is true based on the very definitions of the terms square and equilateral rectangle.

If a statement that uses the is of definition is false, we can use logical grounds to dismiss it. For example, if I were to say that a triangle is a square, we could logically argue that this violates the definitions of triangle and square since a triangle, by definition, has three sides while a square, by definition, has four equal sides.

Similarly, if I were to say that red is blue, we could logically argue that this violates our definitions of red and blue.

Notice how the is of definition is argued on logical grounds (we don’t use empirical evidence to make these arguments). Arguments made on logical grounds are often arguments about the meanings of words.

The is of composition.

We can also use ‘is’ in the compositional sense. This type of ‘is’ can usually be found as ‘noun is noun’. Place gives some examples — ‘His table is an old packing case’ and ‘Her hat is a bundle of straw tied together with string’. If these statements are true, they are not true by definition. It is not the case that her hat is guaranteed to be a bundle of straw tied together with string. It just so happens that, in this case, her hat is composed of a bundle of straw tied together with string.

We can’t use logical grounds to dismiss statements that use the is of composition. If I were to say that my desk is a suitcase, you wouldn’t use logical grounds to prove my statement wrong. Instead, you would look for empirical evidence — you need to go to my office and collect evidence as to whether or not my desk is, in fact, a suitcase. You can’t use logic to assess the validity of my claim — you need science.

The is of predication.

The final ‘is’ is the is of predication. This type of is can be found in the form of noun is an adjective phrase. For example, Superman is six feet tall.

Place explains that if we add ‘and nothing else’ to an ‘is’ statement and the statement makes no sense — the statement is probably using the is of predication. For example, Superman is six feet tall and nothing else does not make sense. Superman is more than the attribute of being six feet tall; he is also an alien from the planet Krypton, has a secret identity, is a pop culture icon, etc. The phrase six feet tall simply describes the height attribute of the noun Superman.

The question is, what ‘is’ is the identity theory using?

We can probably dismiss the idea that the identity theory’s claim that the mind is the brain uses the is of predication. The theory doesn’t seem to claim that the mind simply describes an attribute of the brain. Their claim seems to be stronger than that.

So, the question is — does the identity theory’s claim use the is of definition or the is of composition?

If the is in the statement, the mind is the brain uses the is of definition, the identity theorist would claim that the mind is the brain by definition — the word mind means exactly the same thing as the word brain.

Place argues that critics of the identity theory mistakenly believe this is the claim the theory makes — critics believe it uses the is of definition. Because of this, they argue that the identity theory is subject to the constraints of Leibniz's Law. If the mind and the brain are absolutely identical, then all properties of the mind must apply to the brain and vice versa. As the argument above shows, such an argument would be made on logical grounds and would show the identity theory to be false.

But, Place argues, the identity theory does not use the is of definition — it uses the is of composition. The mind is composed of the brain rather than defined by it. In this sense, the mind and the brain can have different properties while still being identical (in the same way water and H₂O can have different properties but be identical).

When we talk of water, we don’t necessarily conceive of it in the microphysical H₂O sense. We can coherently discuss and observe water at a macroscopic level without knowing its precise composition. The meanings of water and H₂O differ in our conceptual frameworks.

In Part 2 of this series, we mentioned different levels of reality: the fundamental level, the macro level, the constructed level, and illusions. When we talk about water being wet, we are most likely talking about water at the macro level. When we talk about water as H₂O, we are talking at a more fundamental level of reality.

Just because we can talk about water at both the macro and the chemical level does not imply that water and H₂O are fundamentally different things. We do not claim that two things exist — water and H₂O. No! When we talk about water and H₂O, we simply use different words to describe the same phenomenon at different levels of abstraction.

Likewise, the identity theorist claims when we talk about the mind and the brain, we are not talking about two different things — we are simply using different words to describe the same phenomenon at different levels of abstraction.

Place argues that because the identity theory uses the is of composition, it is an empirical scientific hypothesis about the actual composition of mental and physical phenomena in the world. A scientific hypothesis cannot be dismissed purely on logical grounds. Arguments from Leibniz’s Law don’t work for claims that use the is of composition. Place argues that we must turn to empirical scientific evidence about the relationship between consciousness and brain states if we wish to evaluate or disprove the identity theory. Armchair logical analysis is simply insufficient.

Like all consciousness theories, the identity theory draws scepticism from many thinkers. I suspect you may have several reservations, caveats, or objections to this one! I can’t wait to read your comments.

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Next in our series, we will examine an attack on the identity theory’s claim — when we discuss functionalism.

In the meantime, if you are interested in learning about other (non-physicalist) theories of consciousness, you may enjoy the following articles:

Thank you.

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Welcome to Part 2 of our series on physicalism, the theory that the physical world can fully explain consciousness.

This article will draw on concepts we covered in Part 1. So, if you haven’t done so already, you may want to read Part 1 before reading this article, especially if you are new to physicalism theories.

Part 1:

Most evenings, my husband, Pete, and I take a walk to catch up on each other’s day. During these walks, Pete often asks me what I’m currently writing about. When I mentioned this article, he laughed and said, “Okay, so you’re going to try to cover the entire field of metaphysics in 2,000 words!”

He might have had a point.

This is a huge topic. Answering the question of what exists might be an impossible task—even with all the words in the world.

But setting a framework for understanding what types of things might exist in our world and how we might differentiate between them is essential for understanding consciousness and will be especially important for understanding why proponents of each physicalist theory adopt the stances they do.

So, this week, let’s take some tiny steps towards trying to answer the question — what exists?

We’ll do this in 3 steps:

1. First, we will outline a framework to think about what exists,

2. Then, we will see how our physicalist theories fit within this framework,

3. And finally, we will review a radically different way of thinking about what exists.

But first, two quick caveats:

One

This article will borrow heavily from the work of theoretical physicist Sean Carroll. When planning this article, I was wary of committing to any particular framework, as I was concerned that doing so might inadvertently imply an acceptance of the assumptions inherent to the chosen framework.

Understandably, traditional frameworks from philosophers like Aristotle and Plato do not incorporate new scientific understandings from modern physics. Carroll provides a modern physicalist framework that accounts for these scientific developments, making it a good place to start our discussion on physicalism.

Two

Given that emergence will be a key concept in this article, we should try to define it. Emergence refers to the observation that the whole is, or at least seems, greater than the sum of the parts. For example, we know that a table is made of atoms. We are told that atoms are mostly empty space. But somehow, solid tables emerge from the complex way atoms and forces interplay.

Emergence is one of those words that is often used without being clearly defined. It can be used in the weak sense, which means the emergent phenomena could be, at least in principle, explained by its parts. With weak emergence, the emergent property is said to be reducible to its parts. Strong emergence, in contrast, means that the emergent phenomenon is something entirely new that cannot be explained or reduced to its parts.

So what do you think? Do tables emerge from atoms and forces in the weak sense — could we, in principle, explain tables with their fundamental parts? or do tables have properties that cannot be explained or reduced to their parts?

The critical question is….

Are emergent phenomena just a different way of talking about the same thing, or are emergent phenomena something completely new? In other words, are emergent phenomena real or simply illusions that seem real?

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1. A Framework to Think About What Exists

The figure above is from Carroll’s book The Big Picture. The idea behind this image is to distinguish between different levels of reality. There’s a lot going on in this diagram, so let’s break it down.

1. Fundamental level

On the far left of the diagram, is the fundamental, real and objective level. This category refers to the most basic particles, fields, and first principles from which the physical universe seems to be constructed, according to our best scientific understanding. They represent the foundational concrete bits and pieces of reality itself. Examples could include subatomic particles like quarks and leptons, fundamental forces like gravity and electromagnetism, or the most elementary units of space and time.

2. Macro level

The second category, which I call the macro level, includes emergent, real, and objective things. These are the larger-scale objects, entities, and structures we directly experience and interact with daily. Examples include human bodies, animals, planets, stars, tables, and chairs. Interestingly, Carroll includes psychology in this category, which, no doubt, some readers will quibble over.

3. Constructed level

The constructed level includes emergent, real, and constructed things, such as concepts, ideas, and constructs. These things don't have a concrete physical form, yet we treat them as real and critically important aspects of our existence and experience. Carroll includes morality, aesthetics, and meaning in this category. Social constructs like money, marriage, and shared cultural or linguistic frameworks will also be included here.

4. Illusions

Illusions are the concepts, ideas, and constructs that don't correspond to any concrete physical reality but are rather imaginative fictions, hypothetical notions, or products of incorrect beliefs and reasoning. Examples might include movie characters, mythical creatures like unicorns, illusory percepts like visual illusions, or incoherent abstractions like the idea of a married bachelor or a square circle.

After laying out this framework, I would be surprised if you did not question some of the distinctions and assertions made here. For example, we might question whether morality is really subjective or whether something imagined might someday be real.

These are great questions to ask, but in this article, I want to focus on one claim in particular — the claim that so many things should be considered real.

Should we consider emergent things as real things?

Let’s explore an example.

Do ships exist?

If I took my four-year-old nephew to Sydney Harbour and asked him — what is a ship? He would have no problem pointing out several large sea vessels transporting people or goods. He would also have no problem informing me that a small tugboat was not a ship.

If I asked my physicist friend the same question, she might cheekily answer that a ship is simply an arrangement of atoms.

It seems that when we are talking about ships we can talk about them in different ways. Sure, my physicist friend would be correct; at the fundamental level, ships are simply made of protons, neutrons, and electrons. But so, too, is every other physical thing in our universe.

Perhaps ships are best thought of at the macro level — in terms of their shape and size — or maybe the constructed level is more fitting because we define ships as the concept of large sea vessels carrying things.

Defining a ship can be tricky. We often resort to definitions like — a vessel that floats and is larger than 60 meters long. But such definitions are arbitrary. Why 60 meters? Why should a sea vessel that is 59.99 meters long lose its shipiness?

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2. How do the Physicalist Theories Fit Within the Framework?

Let’s tie the above framework with the four physicalist views. As a reminder, here’s a super quick review of the four physicalist views we defined in Part 1:

Identity Theory (aka Reductive Materialism)

Conscious states are identical to brain states.

Functionalism

Consciousness is what the brain does, not what it is made of.

Eliminative materialism

Conscious states, like thoughts, feelings, perceptions, intentions, experiences, beliefs, and desires—don't actually exist.

Non-reductive materialism

Consciousness cannot be completely reduced to physical properties.

Below are four key questions (based on those raised by Carroll in The Big Picture). How we answer these four questions will seriously affect how we think about consciousness and reality. Most of the disagreements between the different physicalist views will be based on disagreements about how we should answer the following four questions.

Question 1: Is the fundamental level the really real level?

Science has developed an intense fascination with probing the fundamental, microscopic levels of existence.

There is often an underlying assumption that goes along with this fascination — the basic building blocks of matter and energy are what reality really is. All other emergent levels are sort of real. Tables are real, but not really real.

If emergent things are not really real, are they part real but also part illusion?

When we talk about consciousness, at what level of reality are we talking? If we think consciousness best fits the fundamental level — does that mean we accept some form of panpsychism? And if we think consciousness best fits an emergent level — does that mean we accept that consciousness is part illusion?

Perhaps the fundamental level isn’t the only real level. Other levels of reality might be just as real. This is the position Sean Carroll takes.

Question 2: To understand something at an emergent level, do we first need to understand the lower levels?

To understand the brain, do we first need to understand quantum mechanics and particle physics? The answer to this question might seem to be an obvious no. Again, Sean Carroll would suggest that it seems obvious that neuroscientists can happily learn about how the brain works without needing to understand the intricacies of quantum field theory and the standard model of particle physics.

However, not all would agree with this seemingly obvious answer. Proponents of strong reductionism would argue that emergent phenomena can only be really understood when explained at the fundamental level. To truly understand something means we have explained it according to the fundamental level.

A reductive materialist might hold that neuroscientists could progress towards understanding how the brain works by studying processes like attention, perception and consciousness, but they would consider such understanding limited and potentially incorrect until it is grounded in a lower-level explanation.

Question 3: Can we learn about something at an emergent level that we can’t learn from the fundamental level? Even if we knew everything there was to know?

If we could understand everything — absolutely everything — at the fundamental level, would we really know everything there is to know about what exists?

If we want to know how the brain works, would understanding all the atoms, particles, forces, molecules, and their relative positions really explain how we remember our first kiss, how the ocean smells after a storm, or the lyrics to our favourite song? It seems that we really do learn something new from the emergent level.

To many, the idea of reducing complex phenomena entirely to the fundamental level is misguided. Projects like the Human Genome Project provide a cautionary tale against making such claims. Initially, scientists made grand promises that mapping the complete human genome would unlock all the secrets of human biology and allow us to explain and treat all diseases and traits.

But the reality wasn’t so grand.

Don’t get me wrong. Sequencing the genome was an incredible scientific achievement that has significantly influenced the field's progress. However, it has become clear that simply knowing the genome sequence is insufficient to fully explain human physiology, behaviour, and the nuances of health and disease. The genome alone does not hold all the answers we hoped it would.

But someone might argue — if we know the genome sequence, do we really know everything there is to know? Perhaps not. Perhaps while our current understanding at the lower level is limited, we rely on higher-level theories to understand our world.

An eliminative materialist might argue that we will rely less on our higher-level theories of consciousness as we discover more about the lower levels. With new knowledge, we might come to understand that we were confused about our higher-level theories. We were incorrect. The phenomena we thought existed don’t actually exist and can be eliminated.

Question 4: Can a theory at an emergent level be incompatible with — literally inconsistent with — a theory at the fundamental level?

Now we are stepping into much more controversial territory. If we answer yes to this question, we are advocating for a type of strong emergence. That is, we believe that the emergent level explains something totally new. Even if we know everything there is to know about the fundamental level, we will never be able to predict or explain the emergent level. The behaviour at the emergent level is not reducible to the sum of its parts.

This is the claim of the non-reductive materialist. The non-reductive materialist agrees that a whole at an emergent level (e.g. a person) is made of fundamental parts like atoms. But they also make a stronger claim. They argue that the person level affects the atoms, which cannot be explained by all the other atoms and forces that make up the person. There is an effect of the whole on the individual parts.

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3. A radically different way to think about what exists.

We’ve seen how reductive, non-reductive, and eliminative materialism might answer these sorts of questions, but functionalism has been a bit quiet on this topic.

Although there are many different versions of functionalism, some functionalist views reject Sean Carroll’s idea of levels of reality, claiming that given our understanding of fundamental physics, this idea doesn’t make much sense. I’m referring here to a branch of functionalism called functional reductionism.

Traditionally, functionalism is a theory about consciousness — it claims that conscious states are functional states — a conscious state is as a conscious state does. But functional reductionism makes a stronger claim, suggesting that it is not just conscious states that are functional states. Proponents argue that everything that exists, from subatomic particles to consciousness, can be fully explained and defined by functions and processes with no remainder. It is ‘functions all the way down.’

Functional reductionism has become increasingly popular in the sciences, particularly in physics, perhaps because of its compatibility with fundamental physical theories like quantum mechanics. For example, Knox (2019) and Lam and Wüthrich (2018) suggest that instead of defining spacetime in terms of a 4-dimensional geometry, spacetime should be explained in terms of its functional role — spacetime is as spacetime does.

This represents a radical departure from our everyday conception of reality. We’ll return to this idea briefly when we discuss functionalism.

But next, in this series on physicalism, we will explore The Identity Theory — the idea that conscious states are identical to brain states.

Leave a comment

Thanks so much for reading this article.

I want to take a small moment to thank the lovely folks who have reached out to say hello and joined the conversation here on Substack.

If you'd like to do that, too, you can leave a comment, email me, or send me a direct message. I’d love to hear from you. If reaching out is not your thing, I completely understand. Of course, liking the article and subscribing to the newsletter also help the newsletter grow.

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I want to personally thank those of you who have decided to financially support my work. Your support means the world to me. It's supporters like you who make my work possible. So thank you.

Regular newsletter readers will be aware of my series on The Five Most Controversial Ideas in the Study of Consciousness. This article can be thought of as an extension of that series and the introduction to a new series on physicalism — the theory of consciousness accepted by almost all neuroscientists and most philosophers.

Physicalism has different types. Technically, not all physicalist views insist that a biological brain is required for consciousness. But let's start with biological brains because all physicalist views agree they can be the reason for conscious experiences (even though some views allow for non-biological systems, too).

Your brain is an amazing thing.

Your brain has about 86 billion neurons. Each neuron, on average, has about 7,000 connections to other neurons. This means your brain has a total of about 600 trillion synaptic connections.

Large numbers like these are difficult to grasp, so let’s put it into perspective.

Imagine a pin-head-size chunk of your brain. Inside this pin-head-size chunk, there would be approximately 480 billion connections. In comparison, there are only 8 billion people living on the planet. So, in one pin-head-sized chunk of your brain, you have about 60 times more connections than there are humans living on the planet!

That is amazing. But is this what makes you — you? Are you simply billions of neurons and trillions of neuronal connections in a physical blob of white and grey biological matter?

This week we’re asking three questions:

1. What is physicalism?

2. Why might someone believe in physicalism?

3. What is the main objection to physicalism?

But first, two caveats:

1. There is a case to be made that physicalism and materialism are different theories of consciousness, but in this article, we will use the terms interchangeably.

2. Mental states is a term often thrown around when discussing physicalist theories. It’s an annoyingly vague term, I know! Writing a clear definition is tough because people disagree about what they are. So, for the purposes of this article, we will define mental states as the thoughts, feelings, perceptions, intentions, experiences, beliefs, desires, emotions, memories and all the other things you think about.

1. What is Physicalism?

There are many different versions of physicalism. But there are three (or four) main ones that I’ll focus on here. I will go into more detail about each view in some upcoming articles, but here’s a summary of the main views:

Identity Theory (aka Reductive Materialism)

The main claim of Identity Theory is that mental states are identical to brain states. When you have a thought or questioning feeling, that mental experience is literally just the firing of neurons and the physical brain being in a particular configuration at that moment.

That questioning thought you are having? It’s nothing but your brain in a particular state. Pain, pleasure, and thoughts are all brain states, no more, no less.

Functionalism

Functionalism, on the other hand, claims that mental states are more about what they do than what they are made of. A functionalist would say pain is not about where it happens in your brain but about its functions in avoiding bodily damage, learning from harmful stimuli, and motivating certain future behaviours.

Just like the function of telling time can be instantiated on different types of clocks — analog clocks made of gears, springs and pendulums, or digital clocks made of microcontrollers, LCD displays, and electronic oscillators — the function of consciousness could (at least theoretically) be instantiated in different types of machinery according to functionalism. As a functional property, consciousness doesn't necessarily need a biological brain; the functions associated with conscious experience could be performed by any system, biological or non-biological, as long as it satisfies the right functional roles.

Eliminative materialism

Eliminative materialists are the radicals of the group! They argue that mental states—concepts like thoughts, feelings, perceptions, intentions, experiences, beliefs, and desires—don't actually exist. Mental states are seen as fictitious constructs invented to provide an intuitive explanation. Eventually, these constructs will be understood as brain processes, and we will do away with the idea of mental states altogether. They will be the relics of an outdated psychology.

Non-reductive materialism

If eliminative materialists are the radical group, non-reductive materialists are the controversial group. Non-reductive materialists believe that while the mind is ultimately physical, mental states cannot be completely reduced to physical properties. The controversy is over whether such a view can be considered to be a physicalist view. While some claim it is, others argue it is really dualism in disguise. For this reason, non-reductive materialism has also been called naturalistic dualism, property dualism, and emergence theory.

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2. Why might someone believe in physicalism?

Physicalism has arguably seen the most widespread acceptance and empirical support of all the philosophical theories attempting to explain consciousness. This is especially true in the neurosciences and cognitive sciences, but even among philosophers, physicalism is the most popular view. According to a recent survey, 56.5% of philosophers hold this view (27.1% were non-physicalists, and 16.4% held other views).

The success of physicalism is largely due to the vast evidence from neuroscientific research, which suggests that subjective experiences are highly correlated with observable physical changes and patterns of activity in the brain.

People put forward general lines of reasoning as evidence for physicalism, such as the success of physical sciences, the unity of the sciences (all sciences reduce to physics), and the causal closure of the physical (all physical events have physical causes). Instead of reiterating those ideas, in this article, let’s focus on some of the neuroscientific evidence that supports a physicalist view.

The developing brain

Babies are born with a fairly undeveloped brain. They have lots of neurons — about 100 billion of them. However, they have very few connections between those neurons. During the first year of life, a baby’s brain rapidly forms connections between neurons at an astonishing rate — more than 1 million new connections every second!

Initially, these connections are established in sensory areas, such as the visual and auditory cortices, allowing the baby to process sights and sounds. Next, language connections are formed, enabling the baby to comprehend and eventually acquire speech. Finally, connections associated with higher cognitive functions like reasoning, problem-solving, and decision-making begin to take shape.

These connections are not random. They are formed in response to experiences the baby encounters. Babies grow up in a variety of different worlds that are constantly changing. A baby that grows up in a small beach town in Australia will have vastly different experiences from a baby that grows up in the bustling city of Tokyo. Each baby’s brain will make connections appropriate for its world.

Consider what would happen if a baby were born in that small Australian beach town but immediately moved and was raised in the bustling city of Tokyo. The baby’s brain would develop in a way that is more akin to other babies raised in Tokyo than it would to Australian baby brains.

The adult brain

The brain is incredibly plastic. Even during adulthood. Connections are pruned and remodelled, strengthening some while eliminating others, gradually customizing its circuitry to fit its environment. This remarkable adaptability allows our brains to thrive in whatever surroundings they find themselves in.

If you decided to take up piano lessons, the area in your motor cortex that represents your fingers would become larger than mine (I don’t play the piano). And if you decided to become a taxi driver in London and learn ‘the knowledge, ’ your posterior hippocampi would become larger than mine.

Your brain changes according to what’s important. It adjusts and changes its connections to do what it needs to do. Do something you already know how to do, and your brain will not be very active. But try something new, especially something challenging, and your brain will look like it’s in overdrive while you figure it out.

So far, we’ve reviewed evidence that the environment and behaviour affect the physical structure of our brains. What about the opposite relationship? What evidence do we have that the brain's structure affects our behaviour?

Brain injury

We have a lot of evidence that damage to certain brain areas causes specific changes in behaviour, cognitive abilities, and conscious experiences. For example, damage to the visual cortex in the occipital lobe can lead to partial or complete blindness. Injuries to Broca's or Wernicke's area will affect language production or comprehension. Lesions in the hippocampus can devastate memory.

But, possibly the most famous case of brain injury causing changes was damage to the prefrontal cortex, which is involved in planning, decision-making, personality, judgment, impulse control, and even fundamental aspects of an individual's persona.

It was 1848. A 25-year-old construction foreman named Phineas Gage was working on a railroad construction project in Cavendish, Vermont. While setting explosive charges to clear rock for the construction project, a premature blast drove a three-foot-long, iron tamping rod straight through Gage's left cheek, behind his eye socket, and out the top of his skull, obliterating a significant portion of his brain's frontal lobe.

Miraculously, Gage survived the accident, but his personality and behaviour underwent a dramatic transformation. The once well-mannered, dependable Gage became capricious, profane, and lacked restraint and social awareness.

Drug effects

It's not only permanent physical brain injury that can have a significant altering effect on conscious experience. Chemical influences from certain drugs can have similarly dramatic effects. Psychoactive drugs like LSD, psilocybin, MDMA, and ketamine offer compelling evidence that our subjective experiences are linked to our brain's neurochemistry.

Similarly, stimulants and depressants can dramatically alter not just our outward behaviour but also our innermost qualitative experiences — our moods, perceptions, thought patterns, and sense of self.

For instance, reuptake inhibitors like SSRI antidepressants modulate serotonin levels. They do this by blocking serotonin reuptake in the synapse so that the serotonin stays in the synapse for longer, stimulating the postsynaptic cell. This seemingly simple trick of ensuring a neurotransmitter continues to stimulate the post-synaptic cell is a useful way to influence mood, cognition, and behaviour. And it is further evidence for the idea that consciousness has something to do with the brain.

Even for those who subscribe to a non-physicalist view of consciousness, where consciousness is seen as non-material, the undeniable dependency of conscious experience on the brain cannot be ignored.

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3. What is the main objection to physicalism?

There are a number of objections to physicalism. Some of them are specific to the different types of physicalism. For example, Leibniz's Law — the law that states that if two entities share all the same properties, they are identical — is usually raised in objection to Identity Theory. The argument is that mental states and brain states have different properties, so they cannot be identical according to Leibniz's Law.

And the argument from introspection — the argument that mental states don't feel like brain states when we introspect or examine our subjective experience — is often raised in objection to eliminative materialism. The idea is that our conscious experiences, such as feeling pain or seeing a colour, seem fundamentally different from the objective, physical processes occurring in the brain, making it difficult to eliminate or reduce mental states to purely physical brain states.

But let’s leave these objections for when we explore each theory in more depth. For now, I want to focus on the one seemingly insurmountable objection that all materialists must face.

The hard problem of consciousness

When it comes to physicalism, there seems to be a gap. An explanatory gap. Critics argue that we can study the workings of the brain all we want, but understanding neurons, neurotransmitters, neural networks, or even brain oscillations will not give us a satisfactory explanation of how we have subjective, phenomenal, conscious experiences.

These critics claim that it doesn't matter how much you look in the brain and at what level of abstraction — you won't find the essence of redness, the visceral feeling of anger, or the qualitative nature of consciousness itself.

The hard problem of consciousness was coined by the Australian philosopher David Chalmers. Chalmers argues that all the facts we outline above about the brain’s processes, mechanisms, and behaviours do not lead to facts about conscious experience. Chalmers agrees—the brain is involved in consciousness. We can explain the brain’s processes—that is the easy problem. The hard problem is answering the question of why these brain processes, mechanisms, and behaviours feel the particular way that they do or why they have any feeling at all.

Each of the different materialist views has a different answer to the hard problem. Here’s a quick summary:

• Reductive Materialism claims consciousness can be accounted for by sensory equipment. For example, a conscious experience of fear can be explained by the sensations in one's body (e.g. increased heart rate, sweating, muscle tension).

• Functionalism claims that consciousness is simply certain functional features of the brain. Pain, for example, is just a brain state with certain inputs (e.g. body damage), outputs (wincing) and other functions (flight, fight, or avoidance). Any state in any physical system (not necessarily a biological brain) that sets up this state would count as pain.

• Eliminative Materialism responds to the hard problem of consciousness by saying that the feeling of what it is like is a kind of myth that science should not take seriously.

• Non-reductive materialists can vary in their answer to the hard problem, but they tend to claim some form of emergence — the brain is greater than the sum of its parts.

These answers to the hard problem might seem unsatisfying. But given their popularity among those who study consciousness for a living, it’s worth considering these theories. So, we will explore them in greater depth in this series on physicalism.

Leave a comment

Thanks so much for reading this article.

I want to take a small moment to thank the lovely folks who have reached out to say hello and joined the conversation here on Substack.

If you'd like to do that, too, you can leave a comment, email me, or send me a direct message. I’d love to hear from you. If reaching out is not your thing, I completely understand. Of course, liking the article and subscribing to the newsletter also help the newsletter grow.

If you would like to support my work in more tangible ways, you do that in two ways:

• You can become a paid subscriber

• or you can support my coffee addiction through the “buy me a coffee” platform.

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Do you have a furry roommate with adorable puppy eyes?

If the answer is yes, I’m a little jealous. But I’m also curious — have you ever noticed your tail-wagging best friend sleeping while twitching or kicking their legs as if running?

To any dog owner, it seems obvious they dream. We try to imagine what the dog might dream about—chasing balls, playing at the park, or eating something yummy.

But is your dog really dreaming?

To you, it may seem self-evident that your canine companion dreams, but to others, those twitching legs and muffled barks are simply involuntary muscle spasms occurring during certain sleep stages. Because of this, questions like — do animals dream? so often results in an impasse.

To avoid this potential stalemate, let’s be clear about what question we are trying to answer. It’s tempting to conflate questions like, do animals dream? with other closely related questions, like what do animals dream about? To help sidestep this issue, let’s break this week’s main question into three parts:

1. Which animals show the physical signs of dreaming?

2. Why would animals need to dream?

3. What might dreams feel like to an animal?

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1. Which animals show the physical signs of dreaming?

When it comes to researching dreaming in other species, scientists face a significant hurdle—how do we measure dreams? How do we observe something as subjective and internal as dreaming in animals that can’t tell us about their dreams?

In human research, a major breakthrough in measuring dreams came approximately a century ago when sleep researchers first identified a distinct stage of sleep—rapid eye movement (REM).

The interesting thing about REM sleep is that our brain’s electrical activity during REM sleep (low-amplitude, desynchronized neural activity) resembles the patterns observed when we are awake. For this reason, the REM sleep stage is also called active sleep (I will use these terms interchangeably in this article). It differs from quiet sleep (or non-REM) stages, which are associated with a lack of movements and high-amplitude slow wave patterns.

The other interesting thing about the REM stage is that it is strongly linked to dreaming. We do dream in other stages of sleep, too, but if you wake someone up during REM sleep, they usually report having vivid dreams about emotional events. Dreams during non-REM sleep are not as vivid or emotional. Non-REM ‘dreams’ are better described as mundane thoughts — they lack the vivid and memorable content of REM dreaming.

Quiet and active sleep in animals

Since REM sleep is closely associated with dreaming in humans, it is natural to wonder whether we see evidence of similar active sleep states in other animals.

Almost every animal sleeps. Even animals without brains, like jellyfish, occasionally become motionless. This non-active sleep is thought to be necessary for essential biological processes such as cell repair, growth, development, metabolism, and stress reduction.

Even though almost every animal sleeps, not all animals engage in active sleep. But many do. It is well-documented that most mammals engage in active sleep. Birds too. But it turns out even animals very different from humans, including reptiles, fish, molluscs, and even fruit flies, engage in active sleep. Below, in Figure 1, we see the possible evolution of active sleep in mammals and birds, which shows that while all animals engage in quiet sleep (purple line), not all animals engage in active sleep (orange line).

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2. Why would animals need active sleep?

This makes us wonder — why? Why would a fruit fly need active sleep? What function does it provide?

Before we try to answer this question, we might want to ask a related question:

Why do we need to sleep at all?

Scientists believe moments of inactivity are important for homeostasis — sleep is when our cells repair, we grow and develop, we clear out waste and regulate our body’s stress.

In light of the need for rest and restoration, non-active sleep makes some sense. But it’s difficult to understand why an animal might need active sleep. Why have the brain activity of being awake while being completely detached from the world?

Any time spent sleeping would put an animal in a highly dangerous condition — a condition that makes the animal an easy meal for a potential predator. So, why would animals spend more time sleeping than is necessary for basic rest and restoration? Evolutionarily, we might expect active sleep to provide an enormous advantage to offset this huge disadvantage. But what could that advantage be?

Emotion regulation?

One of the more popular theories about why we need active sleep is that it is important for emotion regulation. There is ample evidence that people who don’t get enough REM sleep are not as good at processing and regulating emotions as those who do.

For example, in one study, two groups of people were shown many images. Some of those images were a bit distressing (i.e. they made people feel negative emotions), and other images were neutral. When the participants slept that night, one group was allowed to sleep normally, but the other group was deprived of any REM sleep.

The next day, the two groups were shown more images. Half of the images were images shown the day before, and half were new images.

The participants' task was to identify which images they had seen before and which were new. Both groups performed equally well for the neutral images. However, for the images that evoked negative emotions, the group that was deprived of REM sleep performed worse than the normal sleep group. The findings of this study (and those like it) suggest an important role for active sleep in emotion processing.

In animals, some of the most captivating evidence for emotional processing during active sleep comes from octopuses and cuttlefish. These marine creatures are known for their ability to change colour, especially during experiences that involve an emotional state. Remarkably, researchers have observed octopuses and cuttlefish exhibiting these same spontaneous colour and texture changes during periods of active sleep.

I highly recommend taking one and a half minutes to watch this clip of an octopus changing colour while sleeping from Nature on PBS.

Why is emotion regulation important?

There is a lot of evidence to suggest active sleep is associated with emotion regulation. The next question is why? Is emotion regulation so important it outweighs the increased risk of being someone’s lunch?

On first impressions, emotions don’t seem important. But, it turns out, emotions have a very important purpose.

Take some time to think about the last time you felt emotional, for example, joy, sadness, anger, pride, or gratitude. If I were to guess, I’d predict the event that caused this emotion was also (at least a bit) surprising. Emotions tend to be heightened when we are surprised — when our initial predictions are wrong. The more surprising an event, the stronger the emotional response.

Imagine for a moment you are a diehard sports fan. Your team, however, is currently at the bottom of the ladder. This weekend, your team will go head-to-head with the team currently at the top of the ladder. If your team loses this game, they are out of the competition. Considering your team’s poor performance so far this season, you reasonably predict your team will not win this game.

Now, let’s consider two scenarios.

Consider how you would feel if you were wrong and your team did win the game. The euphoria and elation would be intense. Now, consider a fan of the opposing team. They have a reasonable prediction their team will win. How would they feel if their team won the game? Probably not as excited as you would feel if your team won, right?

What do feelings about winning a sports game have to do with dreams?

While predicting the outcome of sports games might seem trivial, making accurate predictions about events in our world is extremely important for survival. If something unexpected occurs that violates our predictions about reality, it would be hugely advantageous to remember both the surprising event and the circumstances that led to it. Imagine that an octopus ventures into new territory, expecting to find small fish to eat. But instead, the octopus narrowly escapes an attack by a sea lion. It would be extremely advantageous if the octopus remembered this shocking event and the events that led to it.

To summarise, so far:

• We have evidence that suggests active sleep plays a role in emotion regulation.

• We also have evidence that suggests emotion regulation plays a role in updating our predictive model of the world.

The question is — could this mean active sleep plays a role in updating our predictive models of the world?

A group of neuroscientists who study sleep in animals proposes this exact idea. These researchers not only suggest that active sleep is widespread in animals but also suggest that the purpose of active sleep is to optimise the animals' ability to accurately predict their world. This ability to accurately predict the world is especially important for animals that move and confront constantly changing environments.

Dreaming might simply be our brain’s way of simulating possible scenarios during active sleep. Just like the virtual reality simulation we find in a first-person video game, dreams allow us to try out potential responses to new environments or situations. We can then use the consequence of these responses to update our predictions about what might happen — all within the relative safety of a simulated environment that doesn’t contain real hazards and dangers.

This gives dreaming a clear adaptive value. Updating our predictive models without needing trial-and-error learning is a major evolutionary advantage. Learning to better predict our world with fewer real-life dangers could outweigh the costs of being detached from the world during sleep.

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3. What might dreams feel like to an animal?

We may never know exactly what specific scenarios a fruit fly dreams about, but we know fruit flies need to make predictions about what happens next. If the researchers are correct, and dreaming is about providing an animal with a simulated environment to refine their predictive models of the world, we might expect there is some experiential aspect to this simulation.

If active sleep is really an animal's brain generating a simulation, are these simulations not a type of conscious experience?

We might wonder about the richness of these simulations. Does a dreaming octopus re-experience hunting for a specific fish in a specific situation? Or is the simulation more simple than that? Perhaps an octopus’s dream is more about updating general sensory predictions and actions involved when pursuing prey, avoiding predators, and exploring new environments than it is about specific detailed situations.

The richness of the ‘dream’ simulation likely depends on the complexity of the animal's predictive modelling capabilities. That is, the complexity of the dream will depend on the complexity of the brain. For a simple animal like a fruit fly, dreams may be very basic simulations compared to the complexity of human dreaming.

As with all research investigating non-human behaviour, we must be careful not to have an overly anthropomorphic view of animals that projects human qualities onto animals. Just because there seems to be an association between active sleep and predictive updating in humans doesn’t mean the same exists in non-human animals. But at the same time, we need to be careful not to make the opposite mistake of an overly anthropocentric view that only considers human experience as relevant.

There is still much more research needed to test and validate the hypothesis that dreaming is the brain’s way of updating its predictive models. So, we need to be careful not to make strong claims at this early stage.

But with that caveat in mind, if the idea turns out to be correct, it may shift the way we think about not just animal dreaming but also consciousness itself. Investigating which animals have active sleep and which don’t might provide insights into understanding how consciousness is built — which is also a popular question among many of us interested in artificial intelligence.

Rather than asking questions like — what do animals dream about? the more relevant question may be — is there anything it feels like to make a prediction?

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I want to take a small moment to thank the lovely folks who have reached out to say hello and joined the conversation here on Substack.

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Welcome to Part 2 in our two-part series on: What is Information? The Ins and the Outs.

Last week, in Part 1, we explored information according to Shannon’s Information Theory — which is a theory of information that is heavily used in the sciences, engineering, and artificial intelligence. If you haven’t done so already, you may want to read Part 1 first before reading this article, especially if you are new to Information Theory.

In this article, we will explore information according to Giulio Tononi’s Integrated Information Theory (IIT) — a popular yet controversial theory of consciousness. You will notice both Information Theory and IIT use similar words when describing what they mean by information, but you will very quickly notice their conceptions of information are radically different.

In this article, we’ll slowly build the definition of information according to IIT, piece by piece. To do this, we will review four key characteristics of information according to IIT. Trying to explain the entire theory in one article is an impossible task. The explanation of IIT I give here is a highly simplified version with necessary omissions. We will explore the theory in more detail, and with a more critical eye, in a future article.

Before we begin, there are two claims we should know about and one thing we should keep in mind.

The first claim IIT makes is that consciousness exists. Consciousness is real in the sense that it is an irreducible phenomenon that cannot be eliminated or explained away, as some eliminative materialism theories claim. Consciousness is where IIT begins; It begins with phenomenology.

The second claim is that all conscious experiences have five essential properties—or axioms. (In scientific theories, axioms are simply the basic assumptions on which a theory is built or founded, i.e. they cannot be inferred from other statements.) One of the axioms of IIT is information. The other four axioms are intrinsic existence, integration, exclusion and composition. So, according to the latest version of IIT (version 4.0):

In this article, we will be introduced to the other four axioms, but only insofar as they help us understand information according to IIT.

And the one thing we should keep in mind is that IIT is a theory about consciousness. The core idea is that consciousness is integrated information. So, information is always mentioned in relation to conscious experience. It is an assumed essential building block of consciousness.

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1. Specific

The first key characteristic is that IIT claims information is specific.

Let’s unpack that.

If you think about all the conscious experiences you have ever had — each experience is unique — it is specifically this experience, not that experience.

The exact conscious experience you are having right now, you have never experienced before. You have never experienced reading precisely this combination of words, with the precise configuration of items in your background, sounds in your ears, and smells in the air. When you combine your current perceptual experience with your current emotional experience and memories, it’s clear that this conscious experience is different from all other possible conscious experiences you have had or ever will have.

It is this differentiation that makes consciousness informative. It is precisely because each conscious experience is specifically this experience and not that experience that makes each conscious experience informative.

However, specificity and differentiation alone do not fully capture what IIT means by information. There are three more characteristics we need to unpack, so let's continue putting the pieces together.

2. Differences that make a difference

The second characteristic draws on Gregory Bateson's definition of information:

[T]he world of form and communication invokes no things, forces, or impacts but only differences and ideas. (A difference which makes a difference is an idea. It is a ‘bit,’ a unit of information.)

—Bateson, 1972, p. 276

What Bateson means here is that information happens when a system differs, and those differences make a difference. Notice how it is only differences that make a difference that count as information.

IIT is a physical theory of consciousness. For biological systems — like humans — the differences that make a difference happen in the physical brain.

Currently, at this precise moment, your brain is in a particular configuration and state. For simplicity, we can think of this as the neurons in the brain being wired up in a particular way, with some neurons firing while others are not (the brain is more complicated than this, but this notion will work here). Let’s call this your brain’s current physical state.

Because IIT is a physical theory of consciousness, your brain's current physical state must differ from all other possible physical states so your current conscious experience differs from all other possible conscious experiences.

And, importantly, for our understanding of information — it is only the difference in the brain’s physical states that makes a difference to itself that counts as information. It’s the differences that make a difference that are informative.

This means IIT’s definition of information is more closely aligned with the etymology— the original, historical meaning — of information than it is with Information Theory.

The word information comes from the Latin informare, which means to give form to or to shape. Historically, it referred to the idea of giving form to the mind or imparting knowledge. So, information in IIT is about the brain’s ability to transform or shape itself in a way that is meaningful to the brain.

Measuring information

To calculate information, IIT adapts concepts from Information Theory, such as entropy and the transmission of information, but applies these concepts in unique ways.

Intrinsic information is measured in units called intrinsic bits, or ibits, to distinguish them from the bits used in Information Theory. An ibit corresponds to a point-wise information value measured in bits but is weighted by a probability.

While I don’t want to spend too much time on the math in this article, those interested in mathy things might find the following helpful (skip the section between the wavey lines if mathy-things is not your thing):

Whereas Information Theory primarily focuses on quantifying how much information is communicated, IIT adapts these principles to understand the causal relationships within a system. Specifically, IIT calculates probabilities to determine how one state of a system can influence another. This involves examining both forward and backward probabilities. The theory can predict how much a specific state leads to or results from another state; that is, it can measure its causal impact. Information is quantified using the following formulas (which use the logarithm of probability ratios, similar to Kullback-Leibler Divergence):

For effect information, forward probabilities calculate the increase in the likelihood of a future state 𝑠‾ given the current state 𝑠.

The formula for effect information:

Conversely, for cause information, the formula incorporates both backward and forward probabilities. The backward probability 𝑃𝑐←(𝑠‾∣𝑠) is calculated using Bayes' rule and reflects how past states influence our understanding of the current state. The forward probability in the logarithmic term calculates the increase in the probability of the current state given a past state.

The formula for cause information:

A more detailed explanation of these formulas is provided on pages 13 and 14 in the latest version of the IIT.

Okay, what does that all mean?

In short, according to IIT, information has what is called cause-effect power. This means information can make things happen and change things in the physical world.

There is a principle in physics called the causal closure of the physical, which asserts that a change in the physical world must have a physical cause. So, if information can make things happen and change things in the world, it must, by definition, be physical.

So, our working definition of information according to IIT is as follows:

We’re getting closer to what IIT means by information, but we have two more pieces to add.

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3. The intrinsic perspective

The third characteristic of information, according to IIT, is that it is not only specific and physical; it is — intrinsic. It’s the difference that makes a difference from the perspective of the system itself.

This is probably the biggest dissimilarity between information according to IIT and information according to Information Theory.

Shannon Information views information from an extrinsic perspective; information is always assessed from the outside observer's perspective. It measures the statistical relationship between inputs and outputs (or unknown to known) rather than any meaning or significance an event might have. The sender and receiver of the inputs and outputs are assumed to understand the meaning, but Information Theory is only concerned with how accurately and efficiently a message is sent and received. It is not surprising, then, that Tononi calls Shannon information extrinsic information.

In last week’s article, we noted two things about information, according to Information Theory, that are important to highlight again here.

1. Observer-independent vs. observer-independent

Information, according to Information Theory, is observer-dependent. When we calculate the bits of information — the number of bits depends on what the observer already knows and what the observer is uncertain about.

In contrast, information, according to IIT, is intrinsic and relative to the system's specific state and is, therefore, observer-independent.

2. Meaningful

Information, according to Information Theory, is entirely about the statistical properties of an event (e.g. flipping over a card in a deck) and the outcome distribution (which card it is) rather than any meaning or significance the event might have.

Information, according to IIT, is intrinsic and inherently meaningful to the system itself. In fact, Tononi goes further and claims that in IIT, information is meaning.

So, our working definition is:

Okay, so information is specific, physical, and intrinsic (which means it is observer-independent and meaningful). We have one final characteristic to add.

4. Integration

The final piece in our definition puzzle is integration. According to IIT, it is not enough for information to be merely present; it must be integrated — the system must have cause–effect power above and beyond its parts.

So, our final definition is something like this:

That is a mouthful!

If you are wondering what integrated means and how it can explain conscious experiences… that is a fantastic question! I’ll try to answer it in our next article on IIT. But for now, I’ll leave you with something to think about.

The ins and outs of information

What if information looks different from the inside of a system than it does from the outside? As the title of this article suggests, while IIT and Shannon's Information Theory seem to offer radically different definitions of information, could they be, in fact, two perspectives of the same underlying phenomenon — the intrinsic ‘ins’ perspective and the extrinsic ‘outs’ perspective, respectively? Or are the two theories talking about two fundamentally different things that merely share the same word?

What do you think? Are we talking about two sides of the same coin, or are these fundamentally different coins altogether?

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Thanks so much for reading this article.

I want to take a small moment to thank the lovely folks who have reached out to say hello and joined the conversation here on Substack.

If you'd like to do that, too, you can leave a comment, email me, or send me a direct message. I’d love to hear from you. If reaching out is not your thing, I completely understand. Of course, liking the article and subscribing to the newsletter also help the newsletter grow.

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This week, we continue our series on The Five Most Controversial Ideas in the Study of Consciousness with Panpsychism. Panpsychism has gained some popularity recently, but it remains one of the more provocative concepts in the philosophy of mind.

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This week, we’re asking three main questions:

• What is panpsychism?

• Why might someone believe in panpsychism? and

• What are the main arguments against panpsychism?

This article is Part 5 in the series on The Five Most Controversial Ideas in the Study of Consciousness.

Part 1:

Part 2:

·Part 3:

Part 4:

Q1. What is Panpsychism?

Panpsychism is a strange one. It’s the idea that everything — from humans and animals to plants, particles and even rocks — is conscious. The idea has gained some popularity recently, but it’s not new. The view has a long history in both Eastern and Western philosophy.

At its core, panpsychism believes consciousness is a fundamental property of the universe, similar to properties like mass or charge. So, consciousness is ubiquitous.

Panpsychism comes in many different flavours. We won’t go into all the distinctions here, but I want to highlight one. Panpsychists tend to split between constitutive and non-constitutive panpsychism. The main difference is that non-constitutive panpsychism believes macro-consciousness, like our consciousness, is not derived from smaller micro-consciousnesses. Instead, macro-consciousness might emerge from matter (perhaps when a system is sufficiently complex or integrated). In contrast, constitutive panpsychists believe macro-consciousness is derived from micro-consciousnesses.

Non-constitutive panpsychism is worth exploring, but let’s leave that for when we discuss Giulio Tononi’s Integrated Information Theory of Consciousness. In this article, we’ll focus on constitutive panpsychism because it is currently the more fashionable form of panpsychism. For brevity, I will use panpsychism throughout this article but just know I mean constitutive panpsychism, not non-constitutive panpsychism.

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Q2. Why might someone believe in panpsychism?

For many, panpsychism provides a middle ground between the unsatisfying views of dualism and physicalism. As we have discussed a few times now, dualism — the view that the mind and brain are made of different substances — is troubled by the interaction problem.

Physicalism—which we haven’t discussed in detail yet—is troubled by the hard problem of consciousness. David Chalmers argues physicalism cannot explain how consciousness—for example, the experience of redness—could possibly be reduced to the brain. It doesn’t matter how much you look; you will never find redness in the brain.

Panpsychism attempts to bridge this divide between dualism and physicalism. It avoids the interaction problem because there is only one substance — the physical. And it avoids the hard problem because consciousness is a fundamental property, not an emergent one.

Panpsychism also avoids another problem that can arise in some forms of physicalism — where exactly do we draw the boundary between consciousness and no consciousness? Most of us would agree humans are conscious. And (I assume) most would agree a light switch is not conscious. What about a bacterium, a sea sponge, an ant, a snake, a dog, a newborn baby? Pinpointing the exact point at which we draw the line between conscious and non-conscious is challenging for some forms of physicalism. Panpsychism avoids this problem because all matter has the fundamental property of consciousness. Panpsychists don’t need to draw a line.

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Q3: What are the main arguments against panpsychism?

There are many problems with panpsychism, but most thinkers see one main problem—the combination problem. We’ll review the combination problem, but first, let’s briefly review the scientific objection.

1. The scientific objection

Panpsychism hypothesises that consciousness is a fundamental property of reality, but some assert it offers no mechanism, explanation, or evidence for this claim. Worse, some argue, even if scientists wanted to find evidence to support this claim, there is no method to test for the presence of consciousness in things like electrons or quarks. Panpsychism can neither be proved nor disproved. Its claims are unverifiable. In science, theories that cannot be proven wrong are called unfalsifiable theories. Unfalsifiable theories are unscientific.

2. The combination problem

The most significant and pressing problem for panpsychism is the combination problem. How can micro-consciousnesses combine to give macro-consciousnesses?

The combination problem is not just one problem. Here, I will focus on just a few of the key issues. For a much more detailed analysis of the combination problem, I recommend The Combination Problem for Panpsychism by David Chalmers.

The subject-summing problem

The core claim of panpsychism is that micro-level entities have consciousness — which we can think of as fundamental micro-consciousnesses. These individually distinct micro-consciousnesses must combine to produce the macro-consciousness we’re familiar with. However, it is unclear how they do this. How do distinct micro-consciousnesses combine into new unified macro-consciousness systems such as brains?

The very idea of combining consciousnesses doesn’t seem to fit with our experience of consciousness. We feel our conscious experience is one unified experience, not a collection of trillions of separate consciousnesses.

Perhaps micro-consciousnesses simply merge together when they are in close proximity to one another. But that doesn’t seem correct, either. Consider a rock composed of billions of micro-consciousnesses in close proximity—there is no evidence this produces macro-consciousness like a brain. And if you put your head near your friend’s head, it doesn’t seem like your consciousness merges with theirs.

Panpsychism does not yet provide a satisfactory explanation for how consciousness combines or why the combining seems to stop at the brain level.

Where do micro-consciousnesses go?

There are a few other tricky problems to address: What happens to the micro-consciousnesses when they combine into macro-consciousness? Do the micro-consciousnesses of particles somehow disappear or get absorbed when integrated into the macro-consciousness of a brain? That seems difficult to swallow — it would mean all the micro-consciousnesses are erased every time matter reorganises.

Alternatively, panpsychism could propose that there is both a macro-consciousness of the entire system—like a human brain—and separate micro-consciousnesses of all the components that make up the system. Each part at each level within that system simultaneously has different consciousnesses in parallel. But that leads to an overwhelming proliferation of consciousnesses at all levels, with no clear divide between conscious wholes and their conscious parts.

One popular way to avoid the combination problem is to claim micro-consciousnesses don’t actually combine at all (this is called the reductionist approach). But this view doesn’t seem to align with our everyday experience of a single unified conscious experience.

3. Panpsychism of the Gaps

There is a theological concept in which gaps in scientific understanding are solved by claiming God provides the explanation. For example, before we understood the biological origins of life, God was the explanation given for the first living organisms. This reasoning is called the God of the Gaps — when there is a gap in our scientific understanding, we fill the gap by defaulting to God.

Some have argued panpsychism does to consciousness what God of the Gaps reasoning does to science in general. Is panpsychism simply Panpsychism of the Gaps? Does panpsychism merely plug our gap in understanding consciousness with the assertion that consciousness is a fundamental property?

For some, claiming consciousness is a fundamental property of the universe solves the problem of explaining consciousness. But for others, there simply isn’t any evidence to justify a belief in the claims. These panpsychism critics argue panpsychism is simply an assertion that, when accepted, avoids the problems inherent in dualism and physicalism, but there are no good reasons to believe it to be true.

For more on this argument, I recommend the following clip where Alex O’Connor interviews Philip Goff:

The Sum Up

Despite its issues, panpsychism remains a popular yet provocative view in the study of consciousness.

Panpsychism is the last theory in our series on The Five Most Controversial Ideas in the Study of Consciousness. Of course, the five ideas I have covered are not the only controversial ideas in consciousness research. A good case could be made for putting all consciousness theories on the list.

Are there any obvious theories I missed? Which theories would you include? Let me know in the comments.

Thanks so much for reading this article.

I want to take a small moment to thank the lovely folks who have reached out to say hello and have joined in the conversation here on Substack.

If you'd like to do that, too, you can leave a comment, email me, or send me a direct message. I’d love to hear from you. If reaching out is not your thing, I completely understand. Of course, liking the article and subscribing to the newsletter also help the newsletter grow.

If you would like to support my work in more tangible ways, you do that in two ways:

• You can become a paid subscriber

• or you can support my coffee addiction through the “buy me a coffee” platform.

Buy me a Coffee?

I want to personally thank those of you who have decided to support my work financially. Your support means the world to me. It's supporters like you who make my work possible. So thank you.

When we think about consciousness, we usually think of a self—everything we experience seems to be happening from a single subjective perspective. The question captivating many thinkers as far back as records go is whether animals do the same. Are animals self-aware?

Before we try to answer that intriguing question, let’s define the scope. Cognitive scientists tend to think about consciousness in three ways: states of consciousness (e.g. sleep, awake, coma, etc.), contents of consciousness (i.e., our experiences, sensations, thoughts and perceptions) and consciousness as self.

Here, we’re interested in the last conception: consciousness as self. Self-consciousness and self-awareness (terms I will use interchangeably in this article) are defined as an individual’s awareness of their existence, separate from others, with their own thoughts, feelings, and existence.

This week, we’re asking two main questions:

1. How do we measure self-awareness in animals? and

2. What does it mean to be self-aware?

Recently, I attended a live recording for the All in The Mind podcast, in which some of my colleagues discussed animal consciousness. That discussion inspired this article.

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Q1: How do we measure self-awareness in animals?

The challenge with animal self-consciousness is how to test for it. We can’t simply ask them. In the 1970s, psychologist Gordon Gallup Jr. developed a clever test that has become the standard indicator for self-awareness in humans and non-human animals: the mirror mark test.

The mirror mark test is a simple test. After an animal (or a child) is familiarised with a mirror, a small mark is secretly placed on the animal. The mark could be paint or a sticker. It is placed where the animal cannot see it without a mirror. With the mark in place, the researchers watch how the animal behaves when in front of the mirror. If the animal uses the mirror to inspect the mark, the animal has passed the test. And the researchers claim the animal understands the reflection is their own. If the animal ignores the mirror or tries to remove the mark in the mirror, the animal has failed the test.

For many years, the list of animals that passed the mirror mark test was limited to humans and great apes. But during the last 20 years, dolphins, killer whales, elephants, magpies, pigeons, manta rays, and cleaner wrasse fish have been added to the list.

Children typically pass the mirror mark test around 18 months of age. Factors like mirror exposure and parenting styles seem to influence the age. For example, kids from certain non-Western cultures with less exposure to mirrors pass the test much later than their Western counterparts.

The cleaner wrasse is possibly the most interesting case. It’s a small fish that feeds on brown-coloured parasites found on larger fish. The cleaner wrasse passes the mirror test. When a brown mark was placed on their throat region, the wrasse would look in the mirror, then go scrape the mark off on the tank’s gravel before returning to the mirror to verify its removal. Interestingly, they did not attempt to remove other coloured marks, suggesting they may only be interested in cleaning colours associated with the parasites they normally eat.

What's strange is not so much that the cleaner wrasse passes the test as it passes when other animals fail. The fact that a relatively simple fish passes while other animals, like dogs, do not has many questioning the validity of the mirror test.

Three main issues are raised:

1. The mirror mark test is a visual test.

Dogs may fail not because they lack self-awareness but simply because they rely more on smell and hearing than they do on vision. If you show a mirror to a puppy, it may try to play with its reflection or bark at it. But at some stage, the puppy turns into a dog and seems to lose interest in the mirror. Why? Does the dog lack self-awareness? or does the dog have self-awareness but is simply uninterested in the mirror because it doesn’t provide smell or sound?

2. The absence of evidence is not the evidence of absence.

When an animal passes the test, we claim it is self-aware. When it fails, we can’t make the opposite claim — we can’t claim the animal is not self-aware. As Carl Sagan so eloquently reminds us — the absence of evidence is not the evidence of absence. Failing the mirror test is not proof an animal lacks self-awareness. They may simply be uninterested in mirrors — or paint marks.

3. Self-awareness is not a dichotomy.

The pass-fail nature of the mirror mark test makes self-awareness seem like an all-or-none phenomenon. Is this true? Is an animal either entirely self-aware or not at all?

Some may wonder whether self-awareness is a spectrum rather than an all-or-none phenomenon. But if this were true, we may expect to see a continuous gradient of self-awareness that correlates with other cognitive abilities. But we don’t find this. Instead, the species that pass the mirror test seems almost sporadic. Some species unexpectedly pass, while others, presumed to be more cognitively advanced, do not. Does this mean self-awareness is not correlated with cognitive complexity? Or is something else going on?

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Q2: What does it mean to be self-aware?

The mirror mark test has some issues. But what if the problem is with how we interpret the results, not with the test itself? Recognising oneself in a mirror may tell us something about an animal’s awareness, but it may not fully capture what we mean by self-awareness.

As humans, we layer so many different features onto the concept of self-awareness. For example, human self-awareness may mean a sense of personal identity that has continuity over time. It may mean the ability to introspect about our thoughts, feelings, memories and experiences. It may mean our beliefs, desires and intentions. It may mean abstract reasoning, thinking about our thinking, and a theory of mind. And it may mean constructing a complex narrative about ourselves as autonomous agents navigating the world.

Does all that go on in a cleaner wrasse?

Perhaps we need to reexamine what we mean by self-awareness. Yes-or-no questions such as, are cleaner wrasse self-aware? are difficult to answer with a simple yes or no. The question carries the human baggage of what we associate with self-awareness.

The mirror mark test may capture some of the features we associate with human self-awareness, but not all. We may want to label these features as self-aware, but we want to qualify our statement by saying cleaner wrasse are self-aware but not with the same features as elephants. And we may want to label elephants as self-aware but not with the same features as humans. We may even want to say dogs are self-aware but not with features captured by the mirror test.

Each species has features required for it to do what it needs to do to survive and reproduce. Those features may include learning, navigating and interacting in its environment, avoiding injury, acquiring resources, or engaging socially. Some of those features may result in behaviours that look a lot like recognising itself in a mirror. But that may not mean the animal has all the features we humans think about when we label ourselves as self-aware.

In this way, self-awareness may not be an all-or-none phenomenon, or a gradient along one dimension, but a label we use to define many different features. Alternatively, it may be a label we want to use to define something far simpler — a core capacity that supports the development of more complex ones.

One final thought

Late last year, footage circulated on social media suggesting a robot called Rob recognised itself in a mirror. There are serious concerns about the legitimacy of this footage, but despite its controversy, the idea is interesting. What would it mean for a robot to pass the mirror test? If it were generative (not pre-programmed), would we label the robot as self-aware? Or would we label the robot as self-aware but qualify our statement by saying it is not self-aware with the same features as humans?

What are your thoughts?

Leave a comment

Thanks so much for reading this article.

I want to take a small moment to thank the lovely folks who have reached out to say hello and have joined in the conversation here on Substack.

If you'd like to do that, too, you can leave a comment, email me, or send me a direct message. I’d love to hear from you. If reaching out is not your thing, I completely understand. Of course, liking the article and subscribing to the newsletter also help the newsletter grow.

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Hello Curious Humans!

This week, we continue our series on The Five Most Controversial Ideas in the Study of Consciousness with Epiphenomenalism. Epiphenomenalism is not just a cool word to say; it’s also one of the most counterintuitive and provocative concepts in the philosophy of mind.

One of the main puzzles in the philosophy of mind is understanding the mind-body problem — how does the mind relate to the brain? How does consciousness — things like feelings and experiences — cause physical actions in the world? Epiphenomenalism challenges our everyday thinking — suggesting that consciousness doesn’t influence our physical actions at all.

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This week in When Life Gives You AI, we’re asking three questions:

• What is epiphenomenalism?

• Why might someone believe in epiphenomenalism? and

• What are the main arguments against epiphenomenalism?

This article is Part 4 in the series on The Five Most Controversial Ideas in the Study of Consciousness. It draws on Part 2, where I discuss René Descartes’s theory of Substance Dualism and the Interaction Problem. If you are unfamiliar with Descartes’s ideas, you may want to pause here and read Part 2 before diving into this one.

Part 1:

Part 2:

Part 3:

Question 1: What is Epiphenomenalism?

Epiphenomenalism is a more recent view of the philosophy of mind. Its main idea is that consciousness is merely a by-product. It is produced by the brain, but it has no influence whatsoever on the brain—or anything else.

The term made its debut back in 1890, introduced by William James in his hefty tome, The Principles of Psychology. In a chapter that might as well have been titled When Humans Act Like Robots, he mentioned the term epiphenomenalism — just once. His more favoured term for the same concept was automaton theory or the conscious automaton theory.

The related word epiphenomenon was originally a medical term from the late 19th century. It was used to describe symptoms that appear alongside a disease but don't actually contribute to it. Epiphenomenon is also used in other disciplines to describe a side effect or by-product; it's there, but it doesn’t cause the main event.

A famous example of an epiphenomenon comes from Thomas Huxley — the renowned biologist. Imagine a steam engine chugging along the countryside, with steam billowing out from its chimney. Atop the engine sits a whistle. When the engineer pulls a lever, the steam rushes through, and the whistle blares its high-pitched song. The sound of the whistle does not propel the engine forward. While the steam engine causes the whistle, the whistle does not affect the steam engine — it doesn't contribute to the engine's power or direction in any way. It's simply a by-product of the steam that's doing the work.

Huxley drew an analogy between our conscious experiences and the whistle of a steam engine. Huxley argued that just as the whistle sound is caused by the engine but does not, in turn, influence the engine, so too is it that our consciousness is caused by our brain but does not, in turn, influence our brain. It’s a one-way relationship.

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Question 2: Why might someone believe in epiphenomenalism?

In Part 2 of this series, we discussed Descartes and his Meditations on First Philosophy. In the Meditations, Descartes develops his theory of substance dualism, claiming that the world is made of two substances: the non-physical mind and the physical world. But the biggest problem for Descartes is the interaction problem. How does the non-physical mind interact with the physical brain? How can any non-physical thing, like a mind that takes up no space and has no physical properties at all, affect the physical world?

Toward the end of Part 2 of this series, I mentioned two main ways to avoid the interaction problem in Descartes's theory. One way is to reject the dualistic separation between the mind and the body and claim there’s just one thing. This is called monism. In Part 3, we explored one form of monism: metaphysical solipsism, the view that everything that exists is the non-physical mind. Another form of monism is physicalism (which we haven’t discussed in depth yet), the view that everything that exists is physical.

I will discuss physicalism in much more depth in future articles, but for now, let’s review a famous thought experiment often used to highlight why someone might not find physicalism appealing.

Mary and her black-and-white room

Mary is a brilliant scientist who is, for whatever reason, forced to investigate the world from a black and white room via a black and white television monitor. She specialises in the neurophysiology of vision and acquires, let us suppose, all the physical information there is to obtain about what goes on when we see ripe tomatoes, or the sky, and use terms like “red”, “blue”, and so on. She discovers, for example, just which wave-length combinations from the sky stimulate the retina, and exactly how this produces via the central nervous system the contraction of the vocal chords and expulsion of air from the lungs that results in the uttering of the sentence “The sky is blue”…

What will happen when Mary is released from her black and white room or is given a colour television monitor? Will she learn anything or not? It seems just obvious that she will learn something about the world and our visual experience of it. But then it is inescapable that her previous knowledge was incomplete. But she had all the physical information. Ergo there is more to have than that, and Physicalism is false.

—Frank Jackson, in Epiphenomenal Qualia, 1982.

Many find epiphenomenalism resonates with their feeling that consciousness must be more than the physical. When Mary is released from her black-and-white room, it seems she would learn something new when she sees red for the first time. Because Mary currently knows everything physical about the world, what she will learn when she is released from the room and sees red for the first time must be facts that are not physical facts. So, what she will learn must be a non-physical fact.

People argue about what exactly this thought experiment tells us, but we'll leave that discussion for another day. For now, it’s enough to understand that for many, Jackson’s thought experiment points them back towards some form of dualism.

Finding Jackson's thought experiment about Mary compelling evidence for the existence of non-physical facts, yet also understanding the infamous interaction problem inherent in Descartes' substance dualism, some turn to the second way to avoid the interaction problem. They deny there’s an interaction at all. Epiphenomenalism provides a way to do just that. Where substance dualism says there is a two-way relationship between the brain and the mind (illustrated on the left in the image below), epiphenomenalism claims the relationship is one-way (right in the image below).

The causal closure of the physical

To understand the epiphenomanalist's claim, we need to review the principle of the causal closure of the physical, which is critical in the mind-body debate.

The idea of causal closure of the physical is that every physical event can be fully explained by preceding physical causes. This means that the physical universe is a closed system when it comes to causality; if you trace the cause of any physical event, you'll end up with another physical event, not something from outside the physical world.

For instance, think about a line of dominos. When one falls and knocks over the next one, the cause of each domino's fall is entirely physical—the push from the previous domino. There's no need to look for a non-physical explanation, like an ethereal spirit or an abstract idea, to explain why the dominos fall.

According to the causal closure of the physical principle, the domino falling must be caused by something physical — in this case, our brain and body. So, our brain forms a motor action that causes our arm to move towards the dominos, and our finger pushes the first domino (represented in the bottom section of the image above). According to epiphenomenalism, at the same time (or perhaps after), the brain must cause a conscious experience of pushing the first domino (represented in the top section of the image above). The conscious experience of pushing the dominos is a by-product of our brain, not the cause of the action itself.

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Question 3: What are the main arguments against epiphenomenalism?

The consequences of epiphenomenalism are pretty wild. Perhaps for that reason, there are several arguments against epiphenomenalism. Let’s focus on just three. The first argument challenges common thinking, the second provides empirical evidence against epiphenomenalism, and the third challenges the logic underlying this view.

1. No free will and no agency

One of the first things to note about epiphenomenalism is the consequence such a view has on our everyday notions of free will and agency. If our consciousness—the reasons we think we do things — doesn't actually cause our actions, then what is consciousness for? This raises the unsettling question of whether we truly have free will and agency over our decisions. Instead, it suggests that our sense of being a conscious decision-maker is, in fact, an illusion. Our actions are determined by unconscious brain processes beyond our conscious control.

According to epiphenomenalism, when you reach for that cookie in the cookie jar, it’s not because you want a cookie. Nope. Your thoughts and wants have nothing to do with it. Your wanting to have a cookie is just an afterthought, a narrative your brain spins up to explain your actions.

If our consciousness, with all its intentions, desires, and decisions, doesn't drive our actions but merely narrates them after the fact, then the idea of free will and agency as we traditionally understand it starts to look shaky. It suggests that we're not genuinely choosing in the way many think we are; instead, our actions are simply the result of our brain processes. In this light, our consciousness is not the director of our actions but the audience member watching them.

If epiphenomenalism is true, then consciousness has no work to do.

Some evidence seems to support the idea of no free will. The famous Libet experiments appear to demonstrate that brain activity associated with decisions occurs before people are consciously aware of making a choice. And the phenomenon of blindsight, where patients with damage to their primary visual cortex exhibit the ability to respond to visual stimuli without consciously perceiving them, suggests a disconnect between consciousness and physical responses. These examples raise the possibility that our subjective experience of making choices and initiating actions may simply be post-hoc explanations constructed by the brain rather than the a priori driver of our actions. What the Libet studies and blindsight tell us about consciousness is a contentious topic, which I will discuss in much more detail in future articles.

For some, the idea that we have no free will is too unsettling to take epiphenomenalism seriously. But even if you're at peace with the notion that free will is an illusion, two other rather thorny issues lurk in the corners of epiphenomenalism.

2. Placebo effects

Most people are probably familiar with the concept of the placebo effect, but just in case you need a refresher, here's how it works: a placebo effect occurs when a person experiences a real physiological response after being given sham treatment that should have no effects. The physiological response occurs simply because the person believes they have received a treatment that does have physiological effects.

For example, in a study looking at the effects of a new drug for hypertension, half of the participants are given the drug (drug group) while the other half are given a sugar pill, which has no active therapeutic ingredients (placebo group). Crucially, the participants are unaware of which group they have been randomly assigned to. The placebo effect can occur when people in the placebo group experience changes they believe to be because of the actual drug. Despite taking a sugar pill, some in the placebo group show reduced heart rate, lower blood pressure readings, and other measurable physiological changes simply because they expect the "medicine" to have such effects. Their belief and expectation that the drug will have an effect results in actual physical changes in line with their expectations, even though they didn’t actually take the drug.

The placebo effect challenges epiphenomenalism because it suggests that our conscious beliefs and expectations can influence our physical body. If conscious experiences were truly epiphenomenal with no causal powers, we would expect that our thoughts would have no measurable influence on our physical biology. The fact that placebo effects happen, sometimes quite significantly, is evidence that our consciousness has physical effects.

3. No effects means no effects. Always.

The fact that I am writing an article about consciousness suggests that consciousness affects my physical brain. Writing is a physical event. How can I write about consciousness if it has no effect on my physical brain? Yet, here you are, reading or listening to this article about consciousness.

To say, “I feel that I am conscious,” I must use my physical body. I must engage my vocal cords, articulate my mouth, and push air through my lungs to produce the sounds that represent the idea that I believe I am conscious. So, my physical body must produce sounds that represent my belief that I am conscious. Yet, according to epiphenomenalism, these vocal sounds cannot be caused by my consciousness because my consciousness has no physical effects. The utterance, ‘I feel that I am conscious’, can only be caused by my physical body. In this framework, my non-physical consciousness is mute—it cannot directly influence my physical actions or communicate its presence. It exists in silence, unable to tell my physical body of its existence or its experiences.

This presents a paradox: If I say, “I feel that I am conscious,” one thing you can know for sure is that I couldn’t be saying this because I was conscious. If consciousness is an epiphenomenon, it wouldn’t be causing our bodies to say it. That would be a contradiction.

When Huxley claims that consciousness is to the brain as the sound of a steam whistle is to the steam engine. He claims that the steam whistle has no effect on the steam engine, and this is true. But the analogy doesn’t quite work. Huxley wants to claim that consciousness is to the physical world as the steam whistle is to the physical world. But this is just not true. The steam whistle does have effects on the physical world. It causes sound. According to epiphenomenalism, consciousness has no physical effects — it does not cause anything.

So we are left with a non-physical mind that not only lacks free will and agency but is also effectively in a locked-in state, utterly detached from the physical and having no effect at all. It does not influence anything.

Some might argue that they still feel they detect a non-physical mind. But even this assertion, if it were true, the act of saying that they detect their consciousness must be an effect of them detecting their consciousness, which is an effect of the epiphenomenon, which is ruled out by definition.

The Sum Up

Epiphenomenalism is one of the more counterintuitive perspectives on consciousness — stripping it of all its power. While some find it potentially resolves the interaction problem inherent in Descartes’s view, it comes with other challenges.

What are your thoughts on an epiphenomenal account of consciousness? Does it resonate with your understanding of the mind-body relationship, or does it raise too many issues to take seriously? I’d love to know your thoughts.

Thanks so much for reading this article.

I want to take a small moment to thank the lovely folks who have reached out to say hello and have joined in the conversation here on Substack.

If you'd like to do that, too, you can leave a comment, email me, or send me a direct message. I’d love to hear from you. If reaching out is not your thing, I completely understand. Of course, liking the article and subscribing to the newsletter also help the newsletter grow.

If you would like to support my work in more tangible ways, you do that in two ways:

• You can become a paid subscriber

• or you can support my coffee addiction through the “buy me a coffee” platform.

Buy me a Coffee?

I want to personally thank those of you who have decided to financially support my work. Your support means the world to me. It's supporters like you who make my work possible. So thank you.

Three articles that got me thinking this week:

By:

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Hello Curious Humans!

This week, we continue our series on the five most controversial ideas in the study of consciousness with solipsism. Solipsism comes in different flavours — in this article, I’ll focus on the most extreme version — metaphysical solipsism.

This philosophical view is a radical one. It’s a belief that the only thing that exists is you.

It’s just you.

Everything else, from the physical world to other minds, does not exist.

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To begin, we will pick up from Part 2, where we explored Descartes and his theory of Substance Dualism. If you haven’t had the chance to read that post, you may want to pause here and read Part 2 before diving into this one.

Here’s a little recap from Part 2:

In the Meditations, Descartes doubts all his beliefs except his ability to doubt. Doubting — being an act of thinking — leads him to realise that if he is doubting, he must be thinking, and if he is thinking, he must exist because he can’t think if he doesn’t exist.

After establishing that he exists, Descartes develops his theory of substance dualism, claiming that the world is made of two substances: the non-physical mind and the physical world.

Towards the end of Part 2, I mentioned some ways to avoid the interaction problem that arises in Descartes's theory. One way to reject the dualistic separation between the mind and the body is to claim there’s just one thing. Under this monist view, there are two main options — everything that exists is physical, or everything that exists is mind.

Metaphysical solipsism — is a version that belongs to the latter option.

This week, we’re asking three questions:

• Why might someone subscribe to metaphysical solipsism?

• What are the consequences of metaphysical solipsism? and

• What are the main arguments against metaphysical solipsism?

But first.

We need to briefly review the distinction between epistemological and metaphysical claims because this distinction will be important to our discussion.

Epistemology

Epistemology is the discipline of philosophy interested in what we can know. Epistemological claims, therefore, are claims about what we can know and how we come to know it.

Metaphysics

On the other hand, metaphysics is the discipline of philosophy interested in what exists. Metaphysical claims are claims about what exists and what it is like.

Okay! Let’s dive in.

1. Why might someone subscribe to metaphysical solipsism?

Rene Descartes was a rationalist.

For this article, the main thing you need to know about rationalists is that they believe there is such a thing as undeniable truths that can be known innately — without any prior observation or experience. So, through the process of reasoning alone, certain facts are self-evident. For instance, a rationalist might argue that the concept of 2 + 2 = 4 represents an undeniable truth about the world, a principle that doesn't require empirical evidence to be validated.

The philosophical counterpart to Rationalism is Empiricism. Empiricists believe that all knowledge comes from our senses. They argue that there's no such thing as innate knowledge; rather, everything we know is acquired through observation and experience.

When Descartes set out to write his most famous work, he wanted to find what, if any, undeniable truths might exist. That is, what could be known with absolute certainty — without relying on observation or experience.

To do this, Descartes used his famous method — the Method of Doubt. This rigorous process involved systematically examining his beliefs and asking — can I know this for sure? If he had any doubts about a belief, he set that belief aside.

It's crucial to understand what Descartes was doing here. This is where an understanding of the difference between epistemological and metaphysical claims is relevant.

When Descartes set a belief aside, he wasn't making a metaphysical claim; he was making an epistemological one. For example, when he set aside his belief in the physical world, he wasn’t claiming that the physical world does not exist. Instead, he was questioning what he could be certain about. He made an epistemological claim — that he could not be certain that the physical world existed.

When reading Descartes’s Meditations, solipsists might arrive at a similar position to Descartes — questioning all beliefs except the belief that one is doubting.

But where Descartes eventually adds back his belief in the physical world, metaphysical solipsists never do this. Instead, they adopt an extreme view — denying all information gained from the senses. They completely reject empiricism.

2. What are the consequences of metaphysical solipsism?

Before we delve into the main arguments against metaphysical solipsism, we must fully grasp the profound consequences of a belief in this view.

Embracing metaphysical solipsism means accepting a reality where nothing—absolutely nothing—outside of one's own consciousness exists.

This doesn't simply mean we are alone in the world; it asserts a devoid of anything physical. There are no other minds and no physical world, not even a universe.

If you subscribe to metaphysical solipsism, you can’t truthfully say something like, “Consciousness happens inside my head” because you don’t actually have a head. You can’t even say that you have a consciousness and I have a consciousness. It’s just you. You are consciousness.

What you perceive as the external world and other people are, in fact, just manifestations of you with no basis in reality. All that exists is you as consciousness.

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3. What are the main arguments against metaphysical solipsism?

I want to highlight four arguments against metaphysical solipsism.

1. The conflation problem.

Metaphysical solipsism makes the error of conflating uncertainty about what exists with non-existence itself.

Let’s be clear about what metaphysical solipsism is doing here.

The solipsist initially makes a claim about knowledge — I cannot be sure that information I gain through my senses is true — but then from this claim about knowledge, the solipsist makes a claim about what exists — because I am unsure about the information I gain from my senses, the information I gain from my senses is wrong — it doesn’t exist.

Notice how anthropocentric solipsism can be — whether or not something exists is contingent on whether or not you are certain of its existence. Why should existence be determined by your ability to be certain of its existence?

Imagine you want to buy a loaf of bread from your local bakery. But you cannot logically know whether or not your local bakery currently has loaves of bread to sell. If uncertainty means non-existence, then being unsure about whether there are loaves for sale at your local bakery would mean there are no loaves of bread for sale at your local bakery.

People do not act in accordance with this logic. If they did, they would never go to the bakery. Because there is always uncertainty about the availability of bread, someone who subscribes to this logic would always believe the bakery has no bread.

The only way you can know about things like the availability of bread at your local bakery is through empirical knowledge — you can’t use rational thought. To know, you must go into the world — specifically your local bakery in this example — and get information through your senses.

2. The language problem

Language poses a significant challenge for metaphysical solipsism.

Language is fundamentally social. If you are the only existence, what would be the point of language? If it’s just you, there seems to be no need to interact with others — because others aren’t real — they are just manifestations.

Ludwig Wittgenstein — the Austrian philosopher — made similar claims, arguing that having language without shared meanings is impossible. Language requires mutual understanding and interaction; we can’t have language without an understanding that we share the same reality, and we cannot have a shared reality in isolation.

What is the point in saying, “My toe hurts” if existence is just you? It would be meaningless. If there are no other conscious minds to understand what you are saying, you’d be talking to yourself.

And remember, you don’t actually have toes or a voice box.

3. The surprise problem

If metaphysical solipsism were true, and you are the only thing that exists, then does this mean you are the creator of everything you perceive?

One view is — yes. You are God — the creator of all that exists within your consciousness.

But this raises a paradox: If you are God, why are you not omniscient? Why do you not know everything?

We don’t tend to go about acting like we know everything. We experience surprise, learning, and uncertainty, which are experiences that are incompatible with the idea of being a god-like creator.

The contradiction within metaphysical solipsism is highlighted in the following joke from Bertrand Russell:

If you were truly the architect of all that exists in your consciousness, why are you suprised by a magic trick, guess what’s behind the wrapping paper of a gift, or even reading this article? If you were God, you would have no concept of the unknown; everything would be as you intended or understood it to be.

But you search Google, read books, and ask your loved ones questions. Why? Because you are not God. Sorry.

4. The pain problem

Some versions of solipsism believe that the external world and other people in that world are part of a game that was created and designed by you for your personal amusement. In this scenario, you construct a reality complete with the illusion of others and intentionally limit your knowledge to enhance the game's enjoyment.

If this is true, we might ask, why design a world like this? Why create a world that includes suffering and horror? What purpose do genocide, childhood diseases, and catastrophic natural disasters play?

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The Sum Up

While many find metaphysical solipsism too extreme or absurd to take seriously, others claim that solipsism is a rational conclusion to make when holding certain views about the legitimacy of empiricism.

What are your thoughts?

Are there any Solipists out there? Let me know in the comments. Just kidding. Let yourself know in the comments.

Leave a comment

Some articles I’ve enjoyed reading this week:

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Agora

Chips

People often say that data is the new oil. If that’s true, then microchips are the new steel. Data is the fuel that powers the digital revolution, while microchips are the hard backbone that enables it. Chips underpin almost every aspect of our modern lives. And yet, we rarely give them a second thought. Computers, the internet, our phones, cars, and TV…

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2 years ago · 8 likes · 6 comments · Matthew Harris

Hello Curious Humans!

Last week I had dinner with my nephew. He’s 8. All boys his age, I am told, will not stop talking about Ghostbusters. My nephew is no exception. We played Ghostbusters. I was the ghost. I got slimed. And all was right with the world.

Until it wasn’t.

It was entirely my fault, of course. I’m sure it had something to do with me asking the wrong question. Or maybe I was being too sciencey. Again. Aunty Suzi!

But we’ll get to that later.

This week in When Life Gives You AI, we’re continuing our series on The Five Most Controversial Ideas in the Study of Consciousness with Part 2: Substance Dualism and the Interaction Problem.

Substance Dualism is the theory of consciousness proposed by René Descartes, who is most famous for the statement, I think, therefore, I am.

This week we’re asking:

• What is Substance Dualism?

• Why does Substance Dualism have an interaction problem? and

• How can we avoid the interaction problem?

But first.

How to pronounce Descartes?

Descartes is pronounced DAY-KART. Descartes was French, so we pronounce D-e-s as “Day”, and the final "s" is silent.

Okay. French lesson is over; let’s dive in!

1. What is Substance Dualism?

Descartes’s most famous work, Meditations on First Philosophy, was first published in 1641.

During this time, philosophers were grappling with one of the big classic philosophical questions — how can we know anything for certain? Many philosophers reasoned that because what we often accept as true is a product of custom and culture, which varies from one culture to the next — knowledge, or truth, is relative. That is, knowledge depends on one’s viewpoint. This is a radical position to take — if knowledge is relative, then certainty is not possible. But this was the prevailing idea at the time.

Descartes was sceptical of this prevailing view. His work in the Meditations focused on finding an answer to one main related question: Is there anything that we can know for sure — without any doubts?

In the first meditation, he notes all the things he believes to be true. He goes through each belief and asks — can I be 100% sure this is true? But he quickly confronts the possibility that an evil demon might be deceiving him about the nature of everything. And, at the end of the first mediation, he ends up at the same conclusion as many philosophers of his time — he doubts the truth of all his beliefs.

But early in the Second Meditation, Descartes arrives at a crucial insight: he cannot doubt his own doubting. This realisation leads him to conclude that, even if an evil demon is deceiving him, the very act of doubting confirms his existence—because doubting is a form of thinking, and one cannot think if one does not exist. So, he discovers one thing he can know for sure: I am. I exist.

Following his realisation, Descartes makes an important claim — a claim that has had an enormous impact on our modern conception of the mind. He asserts that the "I" in "I am. I exist" is a thinking thing that does not have a physical form.

This represents a significant shift in thought. Prior to Descartes, it was common among philosophers to view the mind (or soul) as inseparable from the body. But Descartes makes a distinction between sensation — the feeling of what it is like — and the physical processes. By differentiating sensation from the physical, Descartes laid the groundwork for substance dualism, the idea that our world is made of two distinct substances — physical substances (matter) and non-physical substances (minds). An idea that dominates much of the philosophical discussions about consciousness to this day.

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2. Why does Substance Dualism have an interaction problem?

The concept of non-physical things poses an interesting conundrum. We can’t see non-physical things. We can’t measure them; they don’t take up space; they have no physical properties at all — that’s what non-physical means. Non-physical things are not really things at all. Not in the way we would want them to be if we wanted to study them, like scientists. Indeed, many would argue there are no such things as non-physical things.

My nephew tells me ghosts are non-physical things. They don’t have a body. I am told. They do what non-physical things do, apparently. They go through walls just before you’re about to zap them with your Particle Thrower (a Particle Thrower, I am told, is the blaster attached to a Proton Pack). These non-physical ghosts are hard to catch. I’m not a very good ghost. I am told. So, I am quickly abandoned for the more elusive type of ghosts — the ones throwing plates at our heads and dodging beams of protons being shot from the Particle Thrower.

It was at that moment, amid the imaginary plate throwing, that I made my big mistake. It wasn’t my finest moment. I am embarrassed to admit it. I asked the wrong — very wrong — question.

How can a ghost both be able to go through walls and pick up plates? Why doesn’t the ghost’s hand just go through the plate?

Yes, I know! What type of Aunty do I think I am? Too Sciencey — indeed.

In The Passions of the Soul, Descartes argues that the mind is a ghostly soul that is tethered to the body at the pineal gland in the brain. He chose the pineal gland because he noticed that information comes into the brain in twos — we have two eyes, two ears, and two hands. He reasoned that if information comes into the brain in twos, it must join together somewhere in the brain. The only place in the brain that he could find where this might happen was the pineal gland. All other brain parts came in twos — but the pineal gland — there’s only one of those. So, the ghostly soul must join the body there.

A thought like "I am thirsty," for example, being a non-physical part of the mind, would move the animal spirits, which would, in turn, make small movements in the pineal gland, which had large effects on the body — prompting the sensation of thirst and the subsequent physical action of reaching for a glass of water.

When Descartes was writing about his ideas about dualism, he had a pen pal — Princess Elizabeth of Bohemia. The two would often exchange letters about Descartes's ideas. Princess Elizabeth raises a problem with Descartes's theory in one of those letters. In my words, she asked the following:

How do non-physical thoughts move anything? It seems to me that for something to be moved, it needs to move itself, or it needs to be pushed or pulled by something that is physical. But you have claimed that the mind is non-physical — it takes up no space. How can a non-physical thing that takes up no space have any effects on the physical world at all?

This is the interaction problem. And it’s a big problem. Although Descartes's idea of the mind as separate from the body is currently one of the more popular theories of consciousness, no one has found a scientifically satisfactory way to solve the interaction problem. To solve the interaction problem, we would need to find a mechanism that goes beyond the current laws of physics. There is no empirical evidence of such a mechanism.

When it comes to consciousness, sometimes it feels like there is a point at which we need to take a leap of faith — where logical consistency and scientific facts can only take us so far. For some, substance dualism is the point where they leap.

But for many, Descartes's solution to the interaction problem is not a satisfactory explanation.

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3. How can we avoid the interaction problem?

If we don’t want to leap at substance dualism, we have two main ways to avoid it. We can reject the interaction, or we can reject the dualism.

Rejecting the interaction

We could keep the idea that the mind and brain are separate substances but reject the idea that they interact. Two notable theories under this umbrella are:

• Parallelism, which suggests that the mind and brain are in harmony but don’t interact causally.

• Epiphenomenalism proposes that the brain influences (or emerges from) the mind, but the mind has no influence on the brain. It’s a one-way relationship.

Rejecting the dualism

Alternatively, we could reject the idea that the mind and brain are separate substances. We could do this in a few different ways:

• We could argue for a form of property dualism, where the mind is not a separate substance but a set of properties that emerge from (or are inherent to) the brain. This perspective retains a dualistic view of mind and matter but doesn’t claim that the mind is a separate substance.

• Alternatively, we move to some form of monism, which means we reject the dualistic separation altogether — there’s just one substance. This could lead to either physicalism, where everything is ultimately physical, or a more radical stance that everything is non-physical.

The Sum Up

The biggest challenge for substance dualism is the interaction problem.

And the biggest challenge for playing Ghostbusters is not questioning the physics of ghostly plate handling.

Thanks for being here. In Part 3 of our series on the Five Most Controversial Ideas in the Study of Consciousness, we’ll explore solipsism — the idea that only my mind exists.

Hello Curious Humans!

Remember the movie Transcendence? You know the one where Johnny Depp plays a scientist who has his consciousness uploaded into a supercomputer? Don’t worry if you haven’t seen it — apparently, it was pretty rotten (Rotten Tomatoes: 19% 🤢)

Despite its flop at the box office, the movie’s plot revolves around one fascinating question — is our consciousness just a complex computational process?

Many in the AI and cognitive science community assume it is — which means, many believe that it might be possible to replicate or simulate consciousness in a machine using advanced algorithms and computing power.

Before we dive into some of the arguments for and against this idea, let’s first review the theory that underlies it.

Note: I will use the term mental states throughout this article, which is an annoyingly vague term, I know! Trying to write a clear definition is tough because people disagree about what they are. So, let’s not get tangled in that messy rabbit hole just yet. By mental states, I mean all the thoughts, feelings, perceptions, intentions, experiences, beliefs, desires, emotions, memories and all the other things you think about. We’ll dive into the definitional rabbit hole in another article.

Functionalism

At its core, functionalism is the idea that mental states (thoughts, feelings, perceptions, intentions, and possibly consciousness) should not be defined by what they are made of but, rather, they should be defined by the function or the role that they play. In other words, a mental state is more about what it does than what it is made of.

This concept can seem a bit abstract, so an analogy might help. We tell the time by looking at a clock. But a clock could be analogue — made of gears, springs, and pendulums — or digital, made of microcontrollers, LCD displays, and electronic oscillators. Telling time is best thought of as the function that a clock performs. And it's this function of telling time that's crucial, not the specific materials or components that perform that function.

Functionalism comes in different varieties; some views equate mental states with the functional roles themselves, while others link mental states to their physical states. In this article, I’m going to look at a specific type of functionalism called computational functionalism.

Computational functionalism agrees that mental states are defined by their functional roles, but it goes a step further by specifying that these roles are computational processes. It sees mental states as akin to software running on the hardware of the brain.

Computational functionalism, therefore, subscribes to the idea that mental states do not depend on any specific physical substrate (like the biological brain). Instead, they are substrate-independent. That is, mental states could (at least theoretically) be realised in different physical mediums, provided that the correct functions are produced.

In this week’s issue of When Life Gives You AI let’s:

Take a closer look at computational functionalism by investigating two common objections to the computational functionalist claims:

1. The inverted spectrum thought experiment, and

2. A quantum theory of consciousness

But first, let’s make sure we understand the claims that computational functionalism is making. The chain of reasoning looks something like this:

1. They start by suggesting that every mental state — that is, every thought, feeling, belief, or experience we have — plays a specific functional role. So all mental states are a type of functional state (M → F).

2. They also claim that consciousness is a type of mental state, therefore, just like all other mental states, consciousness is a type of functional state (Con → M).

3. Next, they claim that functional states operate in a way that we can map out and understand in detail, which means (at least in theory) we can compute them (F → C).

4. Together, these ideas come to the conclusion that because consciousness is a functional state, it is mappable, and it is something we can compute (Con → C).

So, if we were going to argue against the computational functionalist view, we might look for reasons why 1, 2 or 3 above are not true.

1. The Inverted Spectrum Thought Experiment

Imagine two people. Let's call them Alice and Bob. Externally, they both seem to react to colours in the same way. They stop at red lights, go at green lights, and so on. However, internally, their experiences of colours are different. What Alice experiences as red, Bob experiences as green, and vice versa. Their colour experiences are inverted relative to each other.

According to functionalism, if two beings (like Alice and Bob) have the same functional responses to stimuli, they should have the same internal experiences. But the inverted spectrum hypothesis suggests that it's possible for two people to have the same functional responses (e.g., both stopping at red lights) while having different internal experiences (seeing different colours).

Implications for Computational Functionalism

If we take seriously the challenges posed by the inverted spectrum thought experiment, we might start to question the soundness of the computational functionalist view.

Let’s review the logic of the computational functionalist view:

1. Premise 1 (P1): All mental states are functional states. (M → F)

2. Premise 2 (P2): Consciousness is a mental state. (Con → M)

3. Premise 3 (P3): All functional states are computable. (F → C)

4. Conclusion (C): Therefore, consciousness is computable. (Con → C)

It seems we have a problem. Premise 1 and Premise 2 cannot both be true if consciousness is not a functional state.

• If consciousness is a mental state (P2), and if mental states include experiences that aren't captured purely by functional states, then not all mental states (including consciousness) are purely functional states (contradicting P1).

• Alternatively, if we insist that all mental states are functional states (P1), then consciousness, which cannot be accounted for by a functional description, might not fit into the category of mental states as defined by P1 (contradicting P2).

If that all sounds too confusing, just know that we are left with the conclusion that consciousness is not a functional state, and if consciousness is not a functional state, then according to P3, it's not necessarily computable.

BUT!! Let's not jump to that conclusion too quickly.

If we decide to reject computational functionalism based on the arguments raised by the inverted spectrum thought experiment — we better be sure that the thought experiment articulates a scenario that is actually possible. To do that we need to review the concepts of conceivability and possibility.

A Note about Conceivability

Thought experiments ask us to conceive of a situation that is beyond our experiences. In philosophy, conceivability is linked with possibility. However, the link between conceivability and possibility is used in different ways.

1. Conceivability as logically possible

The first way we use conceivability is to say that something is conceivable if we can imagine it without encountering any logical contradictions, even though it might not exist in our world. For example, when we watch the movie Star Wars, we can imagine Han Solo's ship, the Millennium Falcon, travelling at the speed of light because, in the Star Wars movie, spaceships exist that can travel at (or faster) than the speed of light.

The logical argument might go something like this:

1. Premise 1 (P1): Spaceships in the Star Wars universe are equipped with hyperdrive technology.

2. Premise 2 (P2): Hyperdrive technology allows for faster-than-light travel by propelling spaceships into hyperspace, where the constraints of normal space-time do not apply.

3. Conclusion (C): Therefore, spaceships in the Star Wars universe can travel at the speed of light (or faster) due to their hyperdrive technology.

This argument is logically valid — the conclusion logically follows the premises. But this sort of argument doesn’t tell us anything about the real world. It’s logically possible, but not necessarily physically possible in our world.

2. Conceivability as logically and physically possible

The second way that we use conceivability is to say that something is conceivable if it is logically possible AND it is physically possible in our world given the laws of physics.

For example, while we might be able to imagine spaceships travelling at the speed of light in Star Wars and lay out a logically valid argument for their possibility, light-speed travelling spaceships are not physically possible in our world.

If the Millennium Falcon travelled at the speed of light in our world, it would, at some point, be dragged into a black hole. To avoid this fate, it would need to travel faster than the speed of light (indeed, Solo claims his ship can travel faster than the speed of light in the movie A New Hope). But, in our world, travelling faster than the speed of light is not possible (or it encounters serious space-time-related problems).

Thought experiments, like the inverted colour spectrum, require us to conceive of a scenario that doesn’t actually exist in our world. When we do this, it is important that we understand the type of conceivability that we need to use.

If we use the first type of conceivability — something is conceivable if it is logically possible — then we can’t say much about whether or not the thought experiment is physically possible in our world. If we want to make claims about our world, we need the second type of conceivability — logically possible and physically possible.

Because Star Wars is a movie, it only needs the first type of conceivability — it just needs to be logically possible. But, the inverted colour spectrum is trying to say something about what is possible in our world, so it requires the second type of conceivability — it needs to be logically possible and physically possible.

Some have argued that while the scenario outlined in the inverted colour spectrum thought experiment might be logically possible — that is, it is logically possible to imagine that someone can experience yellow when we experience blue — further scrutiny reveals that it is not physically possible.

So, let’s take a look at how colour vision works in humans, and test whether the inverted colour spectrum is physically possible.

How colour vision works

As you will recall from high school physics, what we see as colour is actually electromagnetic radiation within a certain range of wavelengths (see Figure 1). Wavelengths within this range (~400 nm to ~700 nm) stimulate certain cells in our retina. Wavelengths outside this range do not stimulate those cells, so we can’t see them.

When we are asked to conceive of an inverted colour spectrum, we need to ask what it is that we are being asked to conceive. Are we to conceive that our perception of the entire electromagnetic spectrum inverts, or just the wavelengths that we see? If we are to conceive that our perception of the entire electromagnetic spectrum inverts, then at what point does this inversion occur? Theoretically, the electromagnetic spectrum is continuous — there is no inherent upper or lower limit to the wavelengths or frequencies that exist.

Putting that aside (let’s just pretend there is some point at which the perception inverts), would this mean that some of us see electromagnetic radiation in some ranges, while others see electromagnetic radiation in other ranges? Surely we could measure this difference? What about radio waves? If our perception of the entire electromagnetic spectrum was inverted for some people, would those people see radio waves and hear colours? Or would sensitivity to different wavelengths also invert?

A perception inversion of the entire electromagnetic spectrum doesn’t seem to make much sense.

What about a perception inversion of just the visible part of electromagnetic radiation? Let’s review how the human eye works to see if this type of perception inversion seems more physically possible.

Most people with normal colour vision have 3 different types of cones in the retina: S-cones, which are sensitive to short wavelengths; M-cones, which are sensitive to medium wavelengths; and L-cones, which are sensitive to long wavelengths.

A cone is a type of cell (a photoreceptor) in the retina that's sensitive to colour and helps provide sharp, detailed vision in well-lit conditions. We use cones mostly during the day, when there’s lots of light.

In the retina, we also have rods — a different type of photoreceptor that's highly sensitive to light, which we use mostly at night or in other low-light conditions. Rods don’t discern color, so they don't contribute to color vision.

In Figure 2 (below) you can see three distinct curves — one for each cone type in the human retina. Each of these curves represents the range of wavelengths that they respond to. For example, S-cones respond mostly to wavelengths of light around 440 nm (which we see as blue).

Our perception of colour can be described along three different dimensions —

1. hue (this is what we mostly think of when we think about colour),

2. luminance (we usually call this brightness), and

3. saturation (the intensity or purity of the colour)

Cone cells play a crucial role in all three of these dimensions.

Hue

In Figure 2 (above), you’ll notice that the activation of the M-cones and L-cones overlap considerably. This overlapping gives us greater sensitivity — or finer colour distinctions. This means we are able to distinguish between different hues better at wavelengths of light where M-cone and L-cone sensitivity overlap (green to red) than at the shorter wavelengths where the S-cones are sensitive (blues). And (perhaps as a result) we have more colour names (hues) for wavelengths of light within the M-L range.

Luminance

The perceived luminance, or brightness, of a colour, is influenced by how much it stimulates the M and L cones. For example, wavelengths of light in the 580 nm range (yellow) stimulate both M and L cones strongly, making yellow appear brighter than, say, blue.

Saturation

All three types of cones contribute to the perception of saturation. For instance, if S-cones are strongly stimulated (with minimal input to M and L cones), the perceived colour would be a highly saturated blue.

Understanding this, we might wonder whether a perception inversion of just the visible part of electromagnetic radiation should involve inverting all colour dimensions (hue, brightness and saturation) or just one dimension. If the perception inversion involves all colour dimensions, we might wonder whether this sort of perception inversion is a type of difference that makes no difference.

What if perception inversion only involves inverting the perceived hue, and perceived brightness and saturation remain uninverted? As cone cells play a crucial role in how we perceive hue, brightness, and saturation, some might argue that this sort of inversion is physically impossible. But, if it were possible, we might wonder what this would mean. Would some people perceive blue as brighter than yellow?

We could spend many head-in-hand hours trying to map different versions of the inverted colour spectrum argument to what we know about colour vision. It would be a mind-bending experience, I’m sure! A functionalist might argue that if we were to do this, at some point, inconsistencies between what it is we are being asked to conceive and what is physically possible would emerge.

Of course, there are those who will disagree with my conception of conceivability as outlined above, but let’s address those concerns when we discuss zombies. For now, it is enough to appreciate that it’s easier to imagine alternative scenarios that feel consistent with the laws of physics than it is to articulate a scenario that is consistent with those laws.

In my quest to try to answer this week’s question — Is Consciousness Computational? — I first outlined the main argument for this view:

1. Premise 1 (P1): All mental states are functional states. (M → F)

2. Premise 2 (P2): Consciousness is a mental state. (Con → M)

3. Premise 3 (P3): All functional states are computable. (F → C)

4. Conclusion (C): Therefore, consciousness is computable. (Con → C)

So far, we’ve explored one type of argument (the inverted colour spectrum argument) that challenges the idea that consciousness is computational by questioning premises 1 and 2. Let’s move on to a different type of argument against computational functionalism — an argument that challenges premise 3.

2. Quantum Consciousness?

Earlier, I mentioned that computational functionalism subscribes to the idea that mental states do not depend on any specific physical substrate — that is mental states are substrate-independent. Just as computer software can run on different computer hardware, computational functionalism believes that mental states can run on different physical forms as long as the right computational processes are in place.

We know that computations are substrate-independent through the work of Alan Turing and Alonzo Church. During the 1930s, while Alonzo Church was working on lambda calculus, Alan Turing was pondering the limits of computation. Both Church's lambda calculus and Turing's Turing machines, in their separate ways, proved the same thing — anything that can be computed by one system can also be computed by the other. This was a huge deal because it suggested a universal concept of computability.

Whether a computation is run on a silicon-based computer, a quantum computer, or even a hypothetical biological computer, the outcome of the computation remains the same, as long as the logic and rules of the computation are preserved. The physical substrate (silicon chips, quantum bits, biological neurons, etc.) is a medium for computation but does not define the computation itself.

So the question is — is this true for consciousness?

So far, computational models have been highly successful in cognitive science and artificial intelligence. We’ve seen computational models successfully simulate language processing, pattern recognition, and decision-making. For example, large language models (LLMs) like ChatGPT that can generate human-like text and engage in seemingly intelligent conversation, highlight the potential of computational models to mimic aspects of human functioning. The recent success of LLMs has many in the AI and cognitive science community feeling confident that a computational approach to understanding the mind is a viable theory.

But, not everyone is so sure.

It turns out that there are aspects of mathematics that cannot be solved computationally.

Turing's work on computability, alongside Gödel's Incompleteness Theorems, exposes fundamental limitations in formal systems, including those that underpin computational systems based on formal logic. Gödel's theorems reveal that within any sufficiently complex formal system (which could inform a computer's logic), certain propositions will be true but unprovable within the system itself. This suggests an inherent incompleteness in such systems. In other words, there are problems that cannot be solved by any algorithm, even with our most advanced computer systems — these problems are called undecidable problems.

The concept of undecidable problems has sparked some intriguing discussions about consciousness. Some theorists ponder whether consciousness might be one of these elusive, undecidable problems.

This line of reasoning aligns with those of Roger Penrose — a renowned physicist and mathematician — and Stuart Hameroff — an anesthesiologist known for his studies in consciousness. Penrose and Hameroff suggest that consciousness might be explained by quantum phenomena, which are beyond the scope of classical computational models.

In the quantum world, particles like electrons or photons can exist in a superposition, meaning they can be in multiple states simultaneously. This superposition is a delicate condition where the quantum particles are perfectly isolated and not interacting with their environment. It's like they are in their own little world, with their states being a well-kept secret. This state is called quantum coherence.

The moment these quantum particles start interacting with their surroundings (like particles in the air, photons from light, etc.), they start to lose this superposition. This process is called decoherence. It's like the particles can't keep their state a secret anymore because the environment “measures” or interacts with them, causing them to “choose” one state over another.

Penrose and Hameroff suggest that consciousness arises from quantum phenomena within the brain's neural structures, specifically in microtubules, which are components of the cell's structural skeleton. Their theory suggests that quantum superpositions and their subsequent collapse in these microtubules produce moments of conscious awareness orchestrated by classical neural signalling (the theory is called the Orchestrated Objective Reduction theory, or Orch-OR).

If the Orch-OR theory holds, and consciousness is a quantum phenomenon, computational functionalism has a problem.

Let’s review the logic of the computational functionalist view one last time:

1. Premise 1 (P1): All mental states are functional states. (M → F)

2. Premise 2 (P2): Consciousness is a mental state. (Con → M)

3. Premise 3 (P3): All functional states are computable. (F → C)

4. Conclusion (C): Therefore, consciousness is computable. (Con → C)

The Orch-OR theory suggests that not all functional states are computable (challenging the notion that F → C), thereby questioning the validity of Premise 3.

But the Orch-OR theory encounters a significant challenge.

The Challenge of Decoherence

Max Tegmark — a physicist and cosmologist known for his work in quantum mechanics — argues that for quantum effects to have any meaningful impact on the brain, quantum states would need to maintain their coherence; that is, they would need to preserve a stable phase relationship necessary for quantum computation. However, Tegmark argues that decoherence — the deterioration of this quantum coherence — would occur too quickly in the brain.

Decoherence happens super fast. And it happens especially super fast in warm and wet environments. The human brain is very warm (38.5°C; 101.3F) and very wet (73% water). Any quantum coherence in the brain would deteriorate on the order of .00000000000000000001 (10^-20) to .0000000000001 (10^-13) seconds. Which is very, very, very, fast. Far too quickly to have a meaningful influence on brain processes.

The Orch-OR theory is highly controversial. Many have criticised it for its serious lack of empirical evidence in support of a quantum account of consciousness. Tegmark is one such critic, arguing that classical physics is sufficient to explain the brain and consciousness without needing to resort to quantum explanations.

The Sum Up

So, there you have it! Computational functionalism holds as a possible theory of consciousness — for now. There are, of course, many other arguments and counter-arguments for and against computational functionalism. But I’m going to leave computational functionalism for a bit.

Starting next week, I’m going to begin a short series on the five most controversial ideas in the study of consciousness. Indeed, many would argue that if your theory about consciousness leads you to one of these ideas — you should probably find another theory! But, how bad are these ideas? Can we learn anything from them?

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In the next issue…

Homunculi in the AI

We often think of consciousness as a movie playing in our heads — like there’s a little person that sits behind our eyes, watching our experiences on a big screen — maybe even directing the show. But when we look inside, of course, we find no miniature version of ourselves — no little screen.

Where does this feeling come from? Why is it so wrong, and what’s really going on?

In the next issue of When Life Gives You AI, I’ll explore the homunculus fallacy — what is it? Whether it’s all that bad? And what it can tell us about conscious AI?

Find it in your inbox on Tuesday, February 6, 2024.

Hello Curious Humans!

Before we start imagining conscious robots — don’t worry, we will get to that shortly, I promise — let’s start with imagining humans.

Imagine a human.

Imagine the human is watching a movie. It’s a comedy, something filled with unexpected twists and laugh-out-loud moments. As the plot unfolds, our human starts making regular, patterned noises and their eyes and mouth contract and relax repeatedly.

Most of us would recognise this behaviour as laughter. We would naturally think that the human is laughing because they've understood a joke or something amusing happened in the movie. We assume the human gets the joke on a conscious level, and their laughter is a direct response to that understanding.

When it comes to consciousness - we judge by watching behaviour. We look at behaviour and guess others are experiencing things similarly to us. If we see someone laughing at a joke, we think they find it funny. We make this assumption because, from our own experience, we usually laugh at jokes when we find them funny.

But this is just an educated guess. We can’t get inside someone else’s head. In philosophy, this problem is called the problem of other minds. We believe we understand others based on their actions and how we would feel or act in similar situations, but in reality, we can't directly access or experience what's going on in someone else's mind. We're essentially making our best guess based on their behaviour and comparing it to our own experiences.

This is a form of abductive reasoning similar to —

However, the situation changes when we think about AI. People start to reason differently here. Let’s take the same thinking exercise as above but slot in an AI robot instead of a human…

Imagine an AI robot. Now, imagine that robot is watching a movie. It’s a comedy, something filled with unexpected twists and laugh-out-loud moments. As the plot unfolds, our robot starts making regular, patterned noises and their eyes and mouth, contract and relax repeatedly.

For some, the question as to whether the robot was, in fact, laughing is not so easily answered. We might question whether the laughing behaviour is caused by a conscious understanding of the humour or just clever programming.

The same abductive reasoning we used for our imagined human doesn’t seem to work as well here.

So here’s the rub. If the AI robot’s laughing behaviour was, in fact, the result of a true conscious understanding of humour, how would we know?

Discerning if an AI robot's laughter is a product of true conscious understanding or a well-programmed response is a real challenge. These sorts of questions aren't just about the technology itself, but they are asking a much deeper question — how do we know what we know? This deeper question is at the root of the branch of philosophy called Epistemology, which urges us to carefully examine the methods, criteria, and evidence we consider necessary to confidently claim knowledge. This week’s question If AI were conscious, how would we know? requires us to reflect on what it means to truly know.

In this week’s issue of When Life Gives You AI let’s:

1. Take a look at the most popular test of AI consciousness — The Turing Test

2. Investigate a popular criticism of the Turing Test — Searle’s Chinese Room Thought Experiment, and

3. Find out what science is doing to try to answer this question

1. The Turing Test

The Turing Test, proposed by Alan Turing in 1950, is a method for determining whether a machine can think. It's a foundational concept in the field of artificial intelligence. If you need a refresher, here's how it works:

1. A human judge engages in a conversation with one human and one machine, both of which are hidden from the judge's view. The conversation typically happens through a computer interface.

2. The judge's task is to determine which participant is human and which is the machine based solely on their responses.

3. If the judge cannot reliably tell the machine from the human, the machine is said to have passed the test.

Turing called this test the Imitation Game. Originally, his idea was that if a machine did well in the Imitation Game, people could reasonably infer that the machine was thinking. Over the years, the phrase The Turing Test has become a more general idea that refers to any form of behavioural test of consciousness. It is this latter interpretation that I use throughout this article (but note that we haven’t actually defined consciousness yet).

The concept of passing the Turing Test is contentious, and the criteria can vary. But there have been several notable developments that are worth mentioning:

• In 1966, Joseph Weizenbaum, created ELIZA — one of the very first chatbots that could mimic conversation. It worked by searching for keywords in the user's input and formulating responses based on that keyword. It would provide vague responses. Although some judges were fooled into thinking they were conversing with a human, it’s hard to imagine a judge being fooled by ELIZA in our current technology climate.

• In 1972, PARRY was a more advanced program that simulated the behaviour of a paranoid schizophrenic. Psychiatrists analysing conversation transcripts were fooled 48% of the time, an impressive result for its time.

• In 2014, Eugene Goostman was a program that simulated a 13-year-old Ukrainian boy. It made headlines for allegedly passing the Turing Test by convincing 33% of human judges that it was a human. However, the setup and methodology of this test faced criticism, particularly regarding the number of judges and the portrayal of the AI as a young non-native English speaker, which might have lowered the judges' expectations.

• Last year, in 2023, there were two notable events — AI in Advertising and GPT-4.

  • AI in Advertising: AI-generated advertisements were indistinguishable from those created by humans in a competition. A panel of marketing experts had only a 57% accuracy rate in distinguishing between AI-generated ads and those made by marketing students.

  • GPT-4: In a public online Turing Test, GPT-4 showed significant improvement over previous models like GPT-3.5. The best-performing GPT-4 prompt had a success rate of 41%, outperforming GPT-3.5’s best score of 14%.

While some have suggested the Turing Test is a reasonable test to determine machine consciousness, many have major objections to the test itself or to how the test results are interpreted. Indeed, there are so many objections to the Turing Test that I could not possibly cover them all here (I’ll leave that for another issue). But I will mention just two.

1. Some of you might be thinking that using the Turing Test in this way makes a huge assumption: that AI consciousness will be just like human consciousness. The original Turing Test was designed as a test of a machine's ability to exhibit intelligent behaviour that is indistinguishable from that of a human. But why should human intelligence (or consciousness) be the criterion? What if AI consciousness were entirely different from human consciousness?

2. The second criticism comes from the philosopher John Searle.

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2. Searle’s Chinese Room Thought Experiment

If you regularly read about AI (or consciousness), you’ve probably heard of Searle’s Chinese Room Thought Experiment. But, just in case you haven’t, or you need a refresher, here’s the set-up:

1. Imagine a person who does not understand Chinese sitting inside a room. This room contains a comprehensive set of rules in English (a sort of manual) that dictate how to respond to Chinese characters inputted into the room.

2. Chinese characters are passed into the room, and the person inside uses the rule book to find the correct responses to these characters, even though they don't understand a word of Chinese. The responses are then passed out of the room.

3. To an outside observer, it appears the room understands Chinese because it can take Chinese questions and produce accurate Chinese answers. However, the person inside the room doesn’t understand Chinese at all; they're simply following a set of instructions.

Searle argues that, similar to the Chinese Room, a computer running a program can process inputs (like language) and produce outputs (like responses) without understanding the input or output in any meaningful way. The computer, like the person in the room, is simply following a set of syntactical rules without any comprehension of the meaning behind them.

Critics of the Turing Test use the Chinese Room Thought Experiment to argue that behavioural tests don’t tell us anything about true understanding. While a machine might act like it has conscious understanding and pass the Turing Test, this does not mean the same thing as genuine understanding.

Searle’s thought experiment has been both influential and controversial. There have been many extensive debates and various counterarguments in the fields of AI and cognitive science.

Here are three common objections:

1. The first objection comes from the philosopher Daniel Dennett. Dennett argues that while the individual (in the room) might not understand Chinese, the system as a whole (the person plus the input plus the rule book) could be said to understand it. Likewise, individual neurons in our brains don't understand language, but the brain as a system does.

2. The second objection criticises the thought experiment itself. Searle’s Chinese Room, as described, would never convince anyone that it was conscious. The simple look-up-table that Searle imagines that matches Chinese characters to English could never produce the sort of results that would pass the Turing Test. It simply lacks the complexity required to produce the sort of responses required to pass the test. Imagine we asked our laughing robot to explain why it was laughing. Any response that convinced us it understood the joke would require far more complexity than a simple look-up table.

3. The third objection is that behavioural tests like the Turing Test are, in fact, sufficient to determine consciousness — in fact, we use them all the time to do just that. Earlier, when we imagined a human laughing at a funny movie, we had no problem ascribing a conscious understanding of the joke to the human just by observing behaviour.

   When we imagined a laughing robot, I suggested that some of us would question whether or not the laughing behaviour was caused by a conscious understanding of the humour or just clever programming. But is that true?

   In popular films like Her and Ex Machina, when AI characters display behaviours typically associated with consciousness—expressing emotions, making decisions, or engaging in meaningful conversations—we easily treat these as signs of a conscious mind. In movies, behaviour is enough for us to assume that the AI is conscious. And if we think it’s not, should we be questioning whether the humans are conscious, too?

The idea that observable behaviour is enough to determine consciousness is rooted in functionalism — the theory that defines consciousness by its functions. If an AI functions like it is conscious — showing responses and adaptations akin to a conscious being — functionalism suggests that it is valid to treat the AI as conscious.

A form of functionalism called computational functionalism is currently the most widely held view among artificial intelligence researchers and many neuroscientists.

So let’s take a look at how neuroscientists are aiming to answer our question — If AI were conscious, how would we know?

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3. The Science of Consciousness

Recently, the renowned journals Nature and Science each published articles addressing our exact question — If AI were conscious, how would we know? The articles were about a report that suggests using what we know about the brain and consciousness to figure out if and how AI could be conscious. The report proposes a checklist of features to look for in AI systems to see how close they are to having a form of consciousness. Right now, no AI has all these features, but the report suggests that it's possible to work towards this.

While this concept of a consciousness checklist is intriguing, it has sparked considerable debate within the scientific community. Objections centre around the following key points.

1. The theories included in the report are theories that are based mostly on data from humans. Some have questioned the relevance of using human-based theories when assessing consciousness in AI.

2. Others have raised questions about what neuroscience is actually measuring. Most neuroscientists who research consciousness do not make the strong claim that they are measuring consciousness itself, but rather, they mostly measure the neural activity associated with a conscious report (ie., what people are saying they are experiencing), which, some argue, is not necessarily the conscious experience.

3. Others object to the checklist itself. To create the checklist, a group of scientists took indicators of consciousness from popular scientific theories. The theories used to create the checklist were only included if they were compatible with a computational functionalist view of consciousness. That is, the theories were included only if they aligned with the idea that consciousness is simply performing the right kind of computations in the right kind of way. You might be wondering, is this consciousness?

All of these objections centre around one fundamental question — what is consciousness?

If you are questioning whether our laughing robot was, in fact, laughing, you might also be wondering whether the scientists are missing something here. Can computation account for what it feels like to experience joy, sadness, daydreams, touch, taste, smells, aspirations, apprehensions, uncertainties, excitement, remorse, and the colour red? Is consciousness computational?

In the next issue…

Is consciousness computational?

Spend any time in the tech community, and you’ll run into the widely held view that sufficiently advanced AI might one day be conscious. Some might even argue that it is not just a future possibility but an imminent reality — sentient computers are already here. But could a computer running algorithms really have conscious experiences? Is consciousness computational?

Find it in your inbox on Tuesday, January 30, 2024.