Overview – Physicalism

Physicalist theories of the mind argue that the universe is made of just one kind of thing: physical stuff.

The opposing view to physicalism is dualism – the view that there are two kinds of things: physical things and mental things (and these mental things are non-physical like a soul or a ghost).

Physicalist theories all agree that the mind is a physical thing. But they disagree about what kind of physical thing mental states are. The syllabus looks at four physicalist explanations of what mental states are:

  • Behaviourism says that mental states are the same thing as behavioural dispositions. So, to be in pain is to say “ouch!”. Or, if someone was to ask you “are you in pain?”, you would say “yes”. To be in pain is to display pain behaviour as well as potential pain behaviour.
  • Type identity theory says that mental states are the same thing as brain states. So, the mental state of being in pain might be the same thing as having the physical ‘c-fibres’ in your brain firing.
  • Functionalism says that mental states are to be understood by their function within the cognitive system. So, pain should be understood as an unpleasant sensation that causes one to avoid bodily harm.
  • Eliminative materialism rejects a key assumption of the other three theories: folk psychology. Instead of seeking to reduce pain to some physical thing, eliminative materialism argues that terms like pain should be eliminated in favour of more accurate descriptions (such as neuroscientific ones).


Behaviourism is the idea that mental states – such as pain, pleasure, sad, happy, etc. – are nothing more than behavioural dispositions.

So, for a behaviourist, to be in pain is to wince, say “ouch!”, try to get away from the source of the pain, and so on. What it means to have the mental state of pain is to display the behavioural dispositions associated with being in pain.

Gilbert Ryle: The Concept of Mind

Arguments against dualism

Ryle’s arguments for behaviourism start with some of the criticisms of dualism we looked at previously – such as the problem of other minds and the problem of causation. He then gives a new argument against dualism: that if dualism were true, mental concepts would be impossible to use.

Consider this: if dualism were true and mental states such as pain referred only to a private and non-physical mental state, how could we ever talk about them? I can’t literally show you what is going on in my mind when I am in pain. You can’t point to a mental state such as pain, you can only point to the behaviour.

Category mistake

Ryle argues that to think mental states are distinct from their associated behaviours is to make a category mistake. He gives the following example to illustrate what he means by this:

Suppose someone were to visit Oxford to see the university. The visitor is shown the library, the lecture theatres, the teachers, and so on. After the tour is complete, he says: “but where is the university?”

The visitor has made a category mistake in thinking that the university is something other than the things he’s been shown already.

Ryle argues that dualists make the same sort of category mistake when talking about mental states.

Suppose an alien were to ask what the mental state of pain is. You show the alien people stubbing their toes, being tortured, wincing, saying “ouch!”, and so on. After showing the alien these examples of pain it asks: “but what is pain?”

In just the same way Oxford University is nothing more than the buildings, teachers, and so on, Ryle is arguing that the mental state of pain is nothing more than the various behavioural dispositions associated with pain. There is nothing you can show the alien over and above these behavioural dispositions.

Behavioural dispositions

An obvious objection to behaviourism is that you can have a mental state but not display any behaviour. For example, you can be in pain but hide the behaviour – perhaps because you don’t want to look like a wimp. Similarly, you can pretend to be in pain when you’re not actually feeling anything, like when a player dives in football.

However, Ryle’s behaviourism is not just about specific behaviours, but also behavioural dispositions.

A disposition is how something will or is likely to behave in certain circumstances. For example, a wine glass has a disposition to break when dropped on a hard surface. The wine glass has this disposition even when it hasn’t been dropped and is in perfect condition.

So, the mental state of pain is not the same thing as simply saying “ouch!”. There is an open-ended and infinite list of hypothetical actions, utterances and behaviours that make up being in pain. For example, if you were to ask someone who just stubbed their toe “did that hurt?”, they would answer “yes”. The person in pain has this disposition even if you never actually ask them the question.

Problems for Behaviourism

Asymmetry between self and other knowledge

When I stub my toe, I have direct access to the feeling of pain it produces. But if I see someone else in pain – however bad – it isn’t as direct. I don’t literally feel their pain (even if it does feel painful to watch).

Further, when I feel pain, there’s no way I could be mistaken as to what I’m feeling. However, if I see someone else scream “ouch!”, I might mistakenly believe they’re in pain when they’re only acting. When it comes to other people’s mental states, I can be mistaken.

It’s clear there’s a big difference between how you experience your own mental states and other people’s. But if behaviourism were true, this shouldn’t be the case.

Remember, according to behaviourism, mental states are behavioural dispositions. So to be in pain is to have certain behavioural dispositions.

It doesn’t feel like that though! If someone were to ask how I know I’m in pain it wouldn’t make sense to answer “because I winced” or “because I said ‘ouch!'” or give some other behavioural explanation. I just feel the pain and know I’m in pain from the unpleasant feeling.

But there’s no room for this ‘unpleasant feeling’ with behaviourism. Behaviourism analyses mental states solely in terms of behaviour.

So, in short, the argument looks like this:

    • Behaviourism seems to rule out any asymmetry between self knowledge and knowledge of other people’s mental states
    • There clearly is an asymmetry between self knowledge and knowledge of other people’s mental states
    • Therefore, behaviourism is false

Ryle’s reply to this problem is to reject the asymmetry between self knowledge and knowledge of other people’s mental states. He argues that this apparent asymmetry is an illusion as a result of having far more evidence in the case of self-knowledge.

Super Spartans

Philosopher Hilary Putnam develops the asymmetry argument further with his example of ‘super Spartans’.

Super Spartans are an imagined community of people who completely suppress any outward demonstration of pain. They don’t wince, flinch, say “ouch!”, or anything like that. They have no dispositions toward pain behaviour whatsoever.

Nevertheless, we can imagine the super Spartans do feel pain internally. They might not show it externally, but they would still experience a subjective experience of pain if they were tortured, say.

Remember, behaviourism says pain is a disposition to behave a certain way. But here we have an example of pain without the associated behavioural dispositions. Therefore the two things – pain and pain behaviour/dispositions – are two separate things. So, if super Spartans are possible, then behaviourism is false.

The behaviourist could reply that without any sort of outward display it would be impossible to form the concept of pain. Without the concept of pain it impossible to distinguish which behaviour they were supposed to be suppressing in the first place. So Putnam’s example is incoherent.


The zombie argument for property dualism can also be used to argue against behaviourism.

A zombie is basically the exact opposite of a super Spartan: where the Spartan has qualia but not behaviour, the zombie has behaviour but no qualia. It might say “ouch!” when it gets stabbed but it doesn’t feel any pain internally.

If zombies are possible, then it’s possible to have the behavioural dispositions associated with pain without actually being in pain. Therefore, the behavioural disposition of pain is separate from the feeling of pain. Therefore, behaviourism is false.


The same mental state can be realised through multiple different behaviours depending on a person’s other mental state. And these other mental states also need to be defined in terms of behaviours, which again might vary depending on a person’s other mental states. This can go on forever.

For example, let’s say you and I could both have the mental state of being thirsty.

This mental state of being thirsty would probably cause you to behave by drinking a drink if it was in front of you. But I might not drink the drink – despite having the same mental state of being thirsty – if I also have the mental state of believing that the drink is poisoned.

So, in order to explain why the mental state of me being thirsty leads to this particular behavioural disposition (i.e. not drinking), we need to appeal to another mental state. But this additional mental state also needs to be analysed in terms of behaviour.

The mental state of believing that a drink is poisoned would probably cause you to behave by avoiding the drink or pouring it away. But someone else might drink the drink – despite also believing that the drink is poisoned – if they also have the mental state of being suicidal.

And the mental state of being suicidal can also be realised in multiple different behaviours depending on a person’s other mental states, and so on and so on.

Circularity objection to behaviourism
Mental states (blue) can be realised by different behaviours (black) depending on other mental states

In short, it seems impossible for behaviourism to explain mental state as behaviours without assuming various other mental states. But these other mental states need a behavioural explanation too!

Type identity

Type identity theory is perhaps the most obvious physicalist theory of mind. It says that mental states reduce to brain states. Put simply, mental states are brain states.

An example often used in philosophy of mind to illustrate brain states is c-fibres. To say someone’s c-fibres are firing is just technical shorthand for the brain state associated with pain.

So, according to type identity theory, to be in pain is identical to having your c-fibres firing. What the word ‘pain’ refers to is the activation of a specific brain area (called c-fibres).

JJC Smart: Sensations and Brain Processes

Ockham’s razor

Note: Ockham’s Razor can be used as an argument against dualism and in favour of physicalism more generally. It’s not just an argument for type identity theory.

Ockham’s razor is a scientific/philosophical principle which says something like:

“Do not multiply entities beyond necessity”

A more colloquial formulation would be something like “the simplest explanation is the best”.

In practice what this means is that, if two theories make the same prediction, the theory that posits the fewest number of entities is likely to be the more accurate theory.

For example, back before it was widely accepted that the earth revolves around the sun, astronomers had to posit all these crazy forces and reasons to explain why planets and stars appeared in the sky when they did.

This geocentric theory could make pretty accurate predictions. But the heliocentric theory made the same predictions using far fewer entities:

Ockham's razor: geocentric vs heliocentric
Geocentric (left) and heliocentric (right)

JJC Smart has a similar idea in mind when arguing against dualism.

If there are no overwhelming arguments or proof of dualism, we shouldn’t posit extra entities to explain the mind. We can explain just as much about mental states by referring to the brain as we can by referring to a non-physical mind.

For example, when I feel pain, certain areas of my brain get activated (let’s call them my c-fibres). And when my c-fibres get activated, I feel pain. This suggests they are the same thing. We don’t need to posit an additional substance.

So, where a dualist would say the c-fibres and the pain are two separate substances, type-identity theory says they are the same physical thing (but different concepts).

‘Pain’ and ‘c-fibres firing’ describe the same thing in the world just as ‘lightning’ and ‘electrical discharge’ describe the same thing using different concepts.

To put it another way, pain and c-fibres are type-identical.


Location Problem

If my c-fibres are firing, it’s presumably pretty easy to locate where this is happening. You could put me in an MRI scanner, for example, and find out the exact location of the c-fibres firing.

But my pain doesn’t seem to have the same physical location. It seems like it’s somewhere else. If you locate my c-fibres it doesn’t seem like you’ve located my subjective mental sensation of pain.

So the argument is something like this:

  • If pain and c-fibres firing are identical then they must share all the same properties
  • C-fibres have a precise physical location
  • Pain does not have a precise physical location
  • Therefore, pain and c-fibres firing are not identical


The zombie argument used against behaviourism can also be used against type identity theory.

Remember, type identity theory says pain is identical to c-fibres firing. But we can imagine a zombie with the brain state (c-fibres firing) but not the mental state (pain).

Multiple Realisability

Hilary Putnam argues that mental states, like pain, cannot be reduced to brain states, such as c-fibres firing, because mental states are multiply realisable. What this means is that the same mental state can come from many different brain states.

For example, an octopus has a very different brain setup to a human. Let’s say, for example, that octopuses have o-fibres instead of c-fibres.

If you stabbed an octopus and it writhed about, surely you would say that it’s because it’s in pain. But if type identity theory is true, this isn’t possible.

Multiple Realisability objection

So the argument is something like this:

  • If type identity theory is true, you cannot have the same mental state without having the same brain state
  • An octopus and a human do not have the same brains or brain states
  • But an octopus and a human can both experience the mental state of pain
  • Therefore, type identity theory is false

An example that Putnam uses is silicon-based aliens. If type identity is true, then we can’t both share the belief “grass is green” because my brain is made from carbon and its brain is made from silicon. But this just seems wrong. We both share the same belief despite our differing physiology.


Think about how you define a knife. You could describe it as a ‘sharp metal object with a handle’ but this would exclude plastic or wooden knives. What’s more important is its function (to cut things).

Similarly, functionalism says that mental states like pain are determined by their function within the cognitive system.

For example, the function of pain might be to cause an unpleasant sensation that encourages one to avoid harm.


When defined in functional terms, pain can be experienced by a human, an octopus or an alien. Thus, functionalism avoids the multiple realisability objection to type identity theory.


Rules out inverted spectrum

What if my experience of green was like your experience of blue and vice versa?

For example, if my qualia when I look at the sea are similar to your qualia when you look at grass.

When we both look at the sea, our mental states would be functionally identical. They would both, for example, cause us to believe “the sea is blue”.

And since our mental states are functionally identical, functionalism must say they are the same mental state. But they’re clearly not the same. My qualia are different from yours.

So the argument is something like:

  • If functionalism is true, then two functionally identical mental states are the same mental state
  • My mental state when I look at the sea is functionally identical to yours but phenomenally different
  • Therefore our two mental states are not the same mental state
  • Therefore functionalism is false

The China Brain

Ned Block’s China Brain thought experiment describes a setup that is functionally identical to a mind but is clearly not the same thing.

These are the key points:

  • Imagine we have a complete functional description of human mental states
  • A human body is hooked up to the entire population of China
  • Every person in China is linked to other people (neurons) via two-way radios
  • They communicate according to the rules set out in the complete functional description of human mental states described earlier
  • Some of these people (neurons) are linked to the outputs of the body
  • Imagine the Chinese population recreated the functions of the neurons
  • So, the input leads to exactly the same output, and everything in between is functionally identical

Basically, the scenario above is designed to replicate a human brain. The population of China is roughly equal to the number of neurons in a brain and the two-way radios replicate the firings of the neurons.

According to functionalism, the China brain would actually be in pain, say, given the appropriate inputs (like being stabbed). But this is obviously false.

Just because the example of the China brain is functionally identical to human pain, doesn’t mean the China brain really is in pain. So functionalism is false. There’s clearly more to mental states than their function.

The Knowledge Argument

A version of the knowledge argument for property dualism can be used to criticise functionalism.

In the original argument, it is argued that all the physical facts would not be enough for Mary to know what it’s like to see red if she’d never seen it for herself. We can adapt this argument to say that all the physical and functional facts would not be enough for her to know what it’s like to see red either. In other words:

  • Mary knows all the physical and functional facts about the mental state of seeing red
  • But when she leaves the black and white room for the first time and sees red she learns something new about the mental state of seeing red
  • So, there is more to the mental state of seeing red than simply the physical and functional facts
  • So, functionalism is wrong – there is more to mental states than their function

Eliminative materialism

Eliminative materialism rejects many of the assumed concepts common to all the other theories we’ve discussed (including dualism).

For example, many of the examples here used the concept of pain, assuming we both had a common understanding of what this refers to. But eliminative materialism doesn’t believe in using these concepts – or similar ones like belief, fear, happy, thought, etc.

Whereas other theories have tried to define these concepts – by their function, or physical instantiation, or whatever – eliminative materialism wants to eliminate them.

Eliminative materialism argues that terms like ‘belief’ and ‘pain’ don’t correspond to anything specific. They might be a useful and practical way of talking about mental states but when we actually look at what they really are, they can’t be reduced to anything in particular.

Eliminative materialists think that a proper analysis of mental states will look more like neuroscience, with specific descriptions of the mechanics of the brain.

Paul Churchland: Eliminative Materialism and the Propositional Attitudes

Folk psychology

Folk psychology refers to the everyday psychological concepts and explanations of behaviour we use. For example:

  • He ran away because he was scared
  • She got a drink because she was thirsty
  • They ran out of the building because there was a panic
  • He studied for the test because he wanted to get a good grade

Folk psychology is such an integral part of our language that it might be hard to even see what it is.  It’s basically just the common sense way we talk about mental states.

The theories we’ve looked at so far seek to define folk psychology terms in various ways. For example, type identity theory reduces the folk psychology concept of pain to c-fibres. And functionalism reduces it to something different – a functional concept.

But both theories implicitly agree that pain is something that can be reduced. They just disagree about what it should be reduced to.

Eliminative materialism rejects the assumption that such folk psychology concepts refer to anything at all. So any reductionist account of mental states – such as type identity theory or functionalism – is doomed to fail. Instead, folk psychology concepts should be eliminated.

Folk psychology as a scientific theory

Folk psychology is something we just assume. But Churchland sees it as a scientific theory like any other. And the nature of scientific progress requires bad theories to be replaced by better ones.

Scientific theories have laws and rules. These laws can be used to make predictions. For example, gravity can predict where Mars will be in the sky on 17th August 2027.

Folk psychology has its own set of laws and rules – but they’re loosely defined. These laws have reasonable predictive power but they’re not perfect. You can often predict how someone will act using folk psychology (e.g. when people get angry they shout and stomp about) – but not always.

There are other problems with folk psychology as a theory. For example, folk psychology can’t explain mental illness, sleep or learning.

And while pretty much every other scientific theory has advanced over time (e.g. Aristote’s physics was replaced by Newton’s and then Einstein’s), folk psychology is still the same as it was thousands of years ago.

Finally, the intentionality in folk psychology doesn’t fit well with most other areas of science. We talk of having a thought about something, for example “I am thinking about an elephant”, but it’s not clear how a physical thing can be about anything in this way. A table or a chair doesn’t have intentionality in this way. It isn’t about anything. You could say a book is about elephants but this is only the case in the minds of people reading it – the physical reality is that it’s just a load of pieces of paper.

Churchland takes all this to suggest folk psychology may not be the most accurate way to think about the mind.

Folk psychology vs. neuroscience

Given the problems with folk psychology described above, Churchland argues we should look to replace it with a more rigorous scientific theory such as neuroscience.

While it may be useful to use folk psychology as shorthand, we shouldn’t take it to be literally true. Engineers often use Newton’s equations to make their calculations because it’s quicker than using Einstein’s and the difference in outcome is so small as to make no difference. But even though Newton’s equations make accurate predictions in this way, they’re not technically accurate.

It’s a similar story with folk psychology vs. neuroscience. Churchland isn’t saying ordinary people should stop using words like ‘belief’ and ‘pain’. However, he is saying that when we’re doing science or philosophy of mind we shouldn’t use folk psychology terms because they’re not technically accurate. We should look to eliminate them in favour of the correct explanations.


Direct certainty of folk psychology

In rejecting folk psychology, eliminative materialism goes against many intuitions we have.

For example, Descartes took ‘I think’ to be his very first certainty. We could argue that the direct certainty we have about our own mental states should take priority over physicalist considerations.

However, this response misunderstands eliminative materialism. Churchland is not denying the existence of the mental phenomena we refer to as ‘beliefs’, ‘pain’, ‘thought’, etc., he’s just saying this folk psychology isn’t the technically correct theory as to their nature.

Folk psychology has good predictive power

Contrary to Churchland’s claims, we can argue that folk psychology does have good predictive power as a scientific theory. For example, you can use it to predict how someone will react when you jump out at them and shout “boo!” or how they’d react if you gave them £1,000,000.

At least at present, neuroscience is pretty bad at making these sorts of predictions. On this basis, folk psychology appears to be the superior scientific theory.

Self refuting

If you interpret Churchland as arguing for his belief in eliminative materialism then you could charge his theory with being self refuting.

All arguments are just expressions of belief. But eliminative materialism claims there are no beliefs. So, in arguing for eliminative materialism, Churchland is expressing his belief in the truth of this theory. But if Churchland has beliefs then this disproves his own theory!

This response clearly commits the fallacy of begging the question. It assumes the very thing it’s trying to prove: that beliefs exist. Churchland could just reply that what his opponent is calling a belief is actually something else (some neuroscience explanation).

But we can push this objection a little further. Eliminative materialism criticies folk psychology for talking about intentional content (i.e. how thoughts can be about something) but offers no neuroscientific alternative.

The very belief (or whatever the eliminative materialist wants to call it) “folk psychology is false” presupposes intentionality. It can be argued that until a plausible neuroscientific alternative for intentionality is given, we cannot eliminate folk psychology as eliminative materialism claims.