The Mind-Body Problem

This problem would be better named ‘the mind-brain problem’. It is the problem of whether the mind IS the brain, or to be more precise, the problem of whether mental states ARE neural states.

The brain

The brain

The average modern person holds a ‘knee-jerk’ type-identity theory. In doing so he doesn’t recognise the mind-brain problem as a problem. Surely, he thinks, modern science has shown us that mental state types (say experiences of red) are identical to neural state types (say neural states n)?

There is a major problem for type-identity theory. It is called the ‘multiple realisability problem’. This problem manifests itself in two sub-problems (i) qualia and consciousness, (ii) rationality and content

The Problem of Qualia and Consciousness



When you experience redness there is something it is like to have that experience. Ditto when you have toothache or are in love. No normal human could ever mistake any one of these experiences for the others – what it is like to have them is essential to the having of them. These ‘something it is like’s are called ‘qualia’ (singular: quale).

The traditional example philosophers use to discuss qualia is the example of pains being said to be (identical to) c-fibre firings (CFF).

So a hypothesis of type-identity theory is that pains are CFFs. And our understanding of mental states like pains is that they necessarily have a characteristic qualia.

Gottfried Wilhelm von Leibniz

Gottfried Wilhelm von Leibniz

Given these two premises then, by Leibniz’ law, the indiscernibility of identicals (if A=B, then any property had by A is also a property had by B), CFFs must necessarily have the characteristic qualia of pain.

By the same token CFFs necessarily have a certain physical shape (that by which we recognise them as CFFs). This means, again by the indiscernibility of identicals, that pains must necessarily have the same physical shape.

But do we believe that all CFF necessarily involve qualia? Or that all pains necessarily have the same physical shape? No, we don’t. Nor should we. It is easy to imagine worlds in which pains are realised by physical states other than CFF. This is a world where pain is realised by states other than CFF (in whales for example).


At the computer

At the computer

Qualitative states are only one type of mental state. The other type are the so-called propositional attitudes. A belief, for example, is an attitude towards a propositional content. So my belief I am at the computer is an attitude (that of belief) to a propositional content [I am at the computer]. I might have a different attitude to the same content (a desire that I am at the computer). Or I might have the same attitude (belief) to a different content [I am asleep in bed].

Just as qualitative states are identified as states with characteristic qualia, propositional attitudes are identified by their contents (and by the type of attitude they are). Qualitative states essentially have qualia. Propositional attitudes essentially have content.

So let’s say a hypothesis of type-identity theory is that beliefs that P are neural state n. And our understanding of beliefs that P is that they essentially have the content P (if they had any other content, or no content at all, they wouldn’t be beliefs that P).

Given these two premises then, again by the indiscernibility of identicals, neural states n must necessarily have the content P.

And by the same token, instances of neural state n necessarily have a certain physical shape (that by which we recognise them as neural state n). This means, again by the indiscernibility of identicals, that beliefs that P must necessarily have the physical shape of neural state n.

But do we believe that neural states of type n necessarily have content? Or that all beliefs that P necessarily have the same physical shape? Again, no we don’t. And again nor should we. It is easy to imagine worlds in which beliefs that P are realised by physical states other than neural state n. Do we imagine that when we finally meet the little green men they won’t be able to believe P?

Multiple Realisability



Knee-jerk type-identity theory falters immediately on the ‘multiple realisability’ of mental states by physical states. Our intuition tells us that one and the same mental state might be enjoyed by creatures with very different physical bodies. If this is the case then the knee-jerk type-identity theory is false.

We might try to escape this conclusion by relativising pains, and beliefs that P, to humans. So we say pain in humans is CFF, beliefs that P in humans is neural state n. But as science tells us, the brain is plastic enough to counter this claim immediately.

We might again relativise to normal humans. But now we are simply engaging in a forlorn attempt to save the theory. Instead we should abandon the identity claim, recognising that whilst there might undoubtedly be a correlation between pains and CFF, and between beliefs that P and neural state n in normal human beings, this correlation does not provide us with evidence for an identity.


Correlations are pesky beasts. They are, for example, our only empirical evidence for causation. So the recognition that As are correlated with Bs is often unthinkingly taken as evidence for a causal relation between A and B when there is no causal relation between them at all (or the causal relation runs the other way, or when A and B have a common cause).

Correlations are also evidence for theoretical identities. Again this means that the recognition that As are correlated with Bs is often unthinkingly taken as evidence for the claim that As are Bs when in fact As are merely correlated with Bs (perhaps because As cause Bs or for all sorts of other reasons).

I hope this piece serves as a warning against unthinkingly adopting the type-identity theory. I hope also that you’ll recognise that nothing I have said here counts as a refutation of physicalism, the claim that mental states are physical states. There are many types of physicalism other than knee-jerk type-identity theory. Perhaps one of these is the right solution to the traditional mind-body problem.

(See readings at the bottom of this piece)


For those who are gluttons for punishment here is the qualia argument logic-book style:

Premise one: Pain = CFF (hypothesis of type-identity theory)

Premise two: Qualia Q is an essential property of pain/shape S is an essential property of CFF

Premise three: If A=B, then any property of A is also a property of B (The Indiscernibility of Identicals)

Conclusion: Qualia Q is an essential property of CFF/shape S is an essential property of pain

The argument is valid, so the conclusion can be rejected only by rejecting one of the premises. I have suggested that the conclusion should be rejected, and that the only premise we can reject is premise one (the hypothesis of type-identity theory).

As you might imagine philosophers have attacked the argument I am offering in all sorts of ways. How would YOU attack it?


SEP Entry on physicalism

Jim Pryor’s piece on Mental States


About Marianne

Marianne is Director of Studies in Philosophy at Oxford University's Department for Continuing Education
This entry was posted in Monthly Conundrums and tagged , , , , , . Bookmark the permalink.

21 Responses to The Mind-Body Problem

  1. Mark Matchen says:

    The knee-jerk type-identity theory you disprove is really a straw man. Maybe not for “the average modern person”, but I think for anyone who’s given it some thought. I don’t even know what it means to say “pains are CFFs”. If I wanted go the biology route, I’d say that c-fibres are peripheral nerves that interact with stimuli and pass an electrical current up the chain. Eventually, these reach a particular brain area, and it’s the firings there that constitute pain. I realize I’m just shifting things around a bit, but that solves your problem of imagining pain or other qualia stimulated in other ways. My definition of qualia becomes, identity with those nerves that produce my conscious states – however they are stimulated – not those that that touch hotplates.

    But that much biology is not the way out I’m looking for. Qualia are conscious states. We have the apparatus now to demonstrate that all mental states are associated with brain activity. As a matter of philosophy, that’s enough – qualia are brain activity. More inclusively, qualia are the operation of whichever physical elements produce conscious states.

    Moving to your Rationality argument, by my definition, there is no core distinction between qualitative states and propositional attitudes. Once you get to the brain, both of them are represented by some brain activity. (You mentioned neural plasticity. Plasticity only supports the idea that different creatures and different people, normal or otherwise, can produce the same qualia with varying activity of consciousness-acting neurons.) I think I’ve also cleared away your Multiple Realisability argument, and not in a forlorn way.

    I am left with the possibility that, in your terms, I’ve been defending Physicalism, not knee-jerk identity theory, in which case, never mind.

    • Marianne says:

      I hope I haven’t presented the knee-jerk theory as a straw man. I try very hard never to do that. I presented it as I am fed it every time I do a lecture on the mind-body problem, and as it is given to me whenever I talk to non-philosophers about the mind-body problem.

      You add that it isn’t a straw man for the average person, for which I thank you. But I did specifically say I was talking about the theory as understood by the average person.

      To say pains are CFFs is to say that there is a psycho-physical bridge law between pains and -C-fibre firings. This is straightforward theoretical reduction, as in heat is molecular motion (i.e. there is a bridge law between heat and molecular motion (i.e. the theory tells us they are the same thing)).

      You seem actually to be embracing type-identity theory when you say “it’s the firings there that constitute pain” How is that NOT the claim pain=C-fibre firing?

      But actually in your next statement you say that qualia are identical to “those nerves that produce my conscious states” and this contradicts your previous sentence – if qualia are identical to c-fibre firings, the firings cannot PRODUCE the qualia.

      I acknowledged explicitly that we can correlate qualia and CFF. I also argued that that ISN’T enough to identify them. So how can you say “As a matter of philosophy, that’s enough – qualia are brain activity.”? Are you suggesting that as science has correlated them, science has shown they are identical and philosophy should shut up? If so I suggest you read again my section on correlation!

  2. Safwan says:

    During a previous online course on the Problem of Body and Mind, I asked this Q.: what do we mean by “Mental States” (MS), and was surprised that no precise definition is offered in philosophy. While my background is engineering, I find it frustrating to deal with philosophical problems, which lack definition. This may lead to situations that most of our dialogue is obscure or incoherent.

    One may think that at least the Body-part (of the Problem of Body and Mind,) – at least the physical aspect – is defined. What is the Physical aspect of phenomena?

    I think that thousands of futile arguments and waste of time could be avoided if we start afresh by defining the concepts we are dealing with. By a proper definition, the problem seems to be at least clear to deal with.

    PHYSICAL: If anything is physical then it can be perceived (and even measured) in time and space. This is the Physical aspect of phenomena: that which is perceived by the 5 senses (and their extensions: tools).

    The 5 Sense Organs are very important in this debate. They constitute “the arbitrator” of what is physical and what is not. All of the 5 Sense Organs interact with a “substance”: matter, colour, smell, taste, acoustical vibrations, temperature…and their integral formation is what constitutes the ‘Body”.

    MENTAL: There is another field of phenomena, however, which does not have ‘substance’ on its own. Feelings, anger, hatred, love, curiosity… intellect, emotions, tendencies… these are inner Mental States. Mental States can be defined as energies, which do not have physical substance and cannot be measured by the 5 Sense Organs.

    Emotions and intellectual states have unique imprint on the neural map, but their “essence” has a completely different nature than the physical world of phenomena. For example: Fear, it is an inner world of great worry – it creates a unique neurological imprint aimed at activating bodily functions associated with Fear: sweating, running, draining blood from the face, widening the muscles of the eyes…etc… All this is “a part of” the phenomenon of Fear, which – itself – has no material component or substance – it is non-substantial in essence.

    The first difference between Physical and Mental aspects – is the issue of the ‘substance’, MS are devoid of substance of their own (substance which could activate the sense organs).

    The second difference is the concept of potentiality:
    Physical states are available in time and space. The Body is one integral existence, which we can point to at any time. Mental States are not one, but many. An infant can display inherently existing potentials displaying Anger, Fear, Joy, Anxiety, Curiosity… but one at a time. Take a toy from a child and Joy disappears and Anger appears. Both Joy and Anger (and other states) are Potentials: possibilities within the Mind, which are activated by external stimuli.

    Western thinking is essentially based on duality and on material perception. I think that a flexibility in philosophical perspectives to view phenomena as non-dual and as “potential possessing”, can turn the debate into a meaningful and beneficial exploration of what constitutes reality of life.

    • Marianne says:

      Oh Safwan, this is a very long post. My heart always sinks when I see a long post – I have so little time to answer. I’ll have to newer this later.


    • Marianne says:

      Hi Safwan,

      Was the online course you did one of ours? Asking what is meant by ‘mental state’ is a bit like asking what is meant by ‘physical state’. Very difficult to give an answer other than a state that is mental. They come in two types: experiential states and propositional attitudes. I explain these in my blog I think.

      In Engineering you can give instrumental definitions. In philosohy we cannot. We are not in the business of defining words, butr of explicating natures. So you might ask ‘what does truth’ mean, and I could give you a dictionary definition, but that won’t amount to a philosophical analysis. Similaly with mental states,. A definition of ‘mental state’ is not use to us, we want to know what mental states ARE.

      If mental states ARE physical states, which many people think, then they do have substance. Indeed they have all the properties that physical states have.

      What do you mean by mental states have a ‘unique imprint on the neural map”?


  3. Safwan says:

    Hi Marianne

    Please agree to explore new perspectives, regardless of wordcount. My heart also sank when i perceived limitation of what i am allowed to convey. I request that you expand the timeslot allowed for exchange of new ideas.

    You used an equation in your Blog: “Leibniz’ law, the indiscernibility of identicals” – So, you agree that clarity is important. I am wondering how can you defend your position that it is difficult to clarify the meaning of words we use: for ex. ‘physical and mental’. It is very easy to clarify what is Physical: it is the field of phenomena which qualities are perceived by the 5 senses. This is the field of science.

    While my Body is Physical, my relationships, however, are motivated by emotions and tendencies: curiosity, anger, love, hatred, etc. These tendencies (and desires) do not have substance of their own. A Physical State has a substance-quality of its own, like body or chemicals – but Mental States do not possesses of a lasting substance.

    They are like “Potential energies” (motivations) which affect the Physical – depending on a trigger or conditions:
    (I gave the ex. of infant’s joy turns to anger when the toy is taken away). Joy and Anger are MS which imprint their related code on the neurological map –( to activate nerves and muscles adequately – or to react). But these various mental energies do not possess a substance of their own. They employ the Physical to their end. But where do MS exist or dwell?

    Your original question is related to this: are MS housed in the Brain? Or they just leave a trace on it when activated?

    I think Philosophy as we know it can be transformed into a new revolutionary (why not?) field of enquiry if we accept new tools. Tools like ‘Nonduality’, ‘Potential States’, or also ‘Neither – Nor’. For ex. Is Colour a PS or a MS? Colour of a flower on that branch – in absence of observer – does not “exist”, (because it is just a level of electromagnetic wave reflected from the flower). When a bird sees it: it is Red, (and this means food is available). The “Redness” is a mental quality (proposional?). But “Red” is also a physical quality – all artist are busy using it in reality. So Colour is neither a PS nor MS, but both. This is the view of ‘Nonduality of Physical and Mental’.

    I would like to ask you whether Philosophy considers the phenomenon of Colour as a Physical S. or a Mental S.


    • Marianne says:

      AAARgh another long one. All very well, for you to say regardless of word counts! I have a full time job! Of course I agree that clarity is important – the whole process of philosophy is that of attempting to clarify things that are murky. You have misunderstood what I said about definitions. There is a difference between offering a definition of a word, offering an analysis of the concept that the word expresses, and offering an account of the phenomenon referred to by that word and that concept. In philosophy our aim is to offer an account of the phenomenon, whilst analysing the concept and SO giving a definite of the word. There is no point starting at the word. Or rather you can start at the word if you like, but you won’t get much of interest (pace the ordinary language philosophy of the middle of the last century).

      I disagree with your definition of physical. There are physical things that can’t be seen by any sense (unless of course we extend the senses with instruments), and there are things that we (arguably perceive) that are not physical (e.g. we see the kindness of an act) – but you will want to say (quite rightly) but what do we mean by ‘perceive’ here. And you are quite right to ask. This is why the meaning of words gets us only a very short way.

      I am sorry, but the perspective you are offering is not, in fact, new.You seem to be expressing dualism of some kind (a physicalist wouldn’t agree that emotions etc do not have substance – as he thinks of them all as physical, and of physical things as having substance, these things must also have substance – another instance of Leibniz’s law).

      It is important to distinguish the idea of a colour and an experience of colour. The latter is mental. The former emerges from an interaction between light’s being reflected from an object and the visual system of a normal human being (under normal conditions). So, yes colours are physical.

      I really would appreciate your writing shorter posts. I don’t mind how many you write, but long posts are hugely off-putting.


      • Zabalawi says:

        I appreciate your busy time Marianne. I will limit my entry here to question your logic:.

        You said: (a physicalist wouldn’t agree that emotions etc do not have substance – as he thinks of them all as physical, and of physical things as having substance, these things must also have substance – another instance of Leibniz’s law). Well:
        Premise1: Physicalist thinks all phenomena have substance
        Premise 2: Emotions are phenomena
        Conclusions: Emotions have substance – no, sorry: Emotions “must have” substance – because all phenomena “have to” abide by the opinion of Physicalist! Leibnitz is protesting in his grave.
        But Physicalist also has emotions and tendencies (such as curiosity, love, hatred and anger or also memory, dreams etc…). These phenomena have no detectable substance on their own (such as mass, heat, colour, smell, acoustical vibrations…which can be detected by the 5 senses and their extensions-tools). The senses and tools do not detect a substance of Anger, Dreams, Memories, Envy, Curiosity, etc.. these belong to Phenomena which are devoid of substance-of-their-own.

        We may realise the level of poverty and hopelessness of current state of philosophy (of Body&Mind) had revealed, producing even such time-wasting ‘conceivabilities’, studying p.Ghosts and p.Zombies, or disposing of the whole Body in the debate.

      • Marianne says:

        Dear Safwan,

        I am not sure what you are objecting to in my argument. I had assumed you would question the conclusion. But the conclusion’s being false doesn’t make the argument a bad one. I was merely saying that you cannot assume that emotions don’t have substance because that is begging the question against the physicalist. You might disagree with the physicalist, but you must have arguments against his arguments.

        But if you think philosophy is such a waste of time, please do not feel you have to come here and discuss it!


      • Zabalawi says:

        No, Marianne, I did not say that Philosophy is a waste of time. I pointed to the problem of lack of basic clarity of what is Physical phenomenon and Mental State. You failed to answer such basic questions about subjects you are vocal about. Asking you what is meant by Mental State you said: “Asking what is meant by ‘mental state’ is a bit like asking what is meant by ‘physical state’. Very difficult to give an answer other than a state that is mental”. So, what is a Mental state in Philosophy of Mind? Your answer was that It is a state which is mental!

        Such vagueness would inevitably lead to separating the body from the mind (p.Zombies) – while in your proposal, you suggested disposing of the body altogether, shifting the problem to Brian-Mind. If you find such time-consuming arguments valuable, it is only normal that you would stick to them and not consider them a waste.

        In any field of enquiry you may find challenging ideas. I think the way we face these challenges expresses our capacity and sense of exploration. There is a difference between an open-minded philosopher and a fundamentalist.
        If your student, questioning your perspective on a certain concept – would be discouraged from continuing the dialogue, then this will be for both a matter to ponder about.

      • Marianne says:

        I am sorry to be so vague and unhelpful.

  4. Paul Conlan says:

    I’d certainly attack P1 (although presumably if one wanted to take the eliminative materialist stance one could attack P2). The route I’d take (and the one which got most traction in the philosophy of mind seminars I was part of) is that if Pain = CFF (or any specific biological process one cares to name), then squid, for example, or any creature without C-fibres does not feel pain. We could propose a second type of pain, called squidpain which is the “same sort of thing” as human pain but the identity between the neural machinery and the pain is different. Then, however, we would be required to do this for every individual case of x-pain which presented us with a new identity. This seems pretty suspect to me.

    Much easier and cleaner to adopt a token-identity theory whereby every mental state is physically caused but need not be identical to the physical cause.

    • Marianne says:

      Hi Paul,

      P1 is the Identity-Theory hypothesis. Anyone who rejects IT would question it. And I think they would be quite right to do so. The argument you give is a good one, and any sort of non-reductive physicalism (token identity theory) would be preferable. But there are philosophers, excellent philosophers, like Jaegwon Kim, who insist that physicalism will fail without a type-identity theory.


  5. Safwan says:

    In fact you were helpful in clarifying vagueness of concepts of Mental and Physical. Thank you Marianne for the opportunity, and good luck.

  6. Safwan says:

    I was watching your lecture (Identity theory) on youtube, and I congartulate you on a great ability to deliver information to listeners. This does not mean that I would agree with everything said. In any case, I think that the basic problem in misunderstanding lies lack of a definition of the phrases we use (Mental and Physical states). I need more time to elaborate – but I want also to thank you for the lecture which I enjoyed.

    • Marianne says:

      Thank you for your kind words about my lecture Safwan. You are not required to agree with everything I say.

      • Zabalawi says:

        Once again I thank you Marianne, for your video-lectures I am enjoying. In particular the explanation about the Chinese Room was quiet illustrative. I intend to write an article to refute the argument, based on the observation that: if one reads – for example – a piece of poetry, and the words truly move the heart of the person, then we can infer that the same (or similar) Mental State of the poet was transferred to the reader. This observation gets stronger if the poetry was translated from another language.

        Here is a poetry about love written almost 4000 years ago in Hieroglyphs, translated into English:
        With sickness faint and weary
        All day in bed I’ll lie;
        My friends will gather near me
        And she’ll with them come nigh.
        She’ll put to shame the doctors
        Who’ll ponder over me,
        For she alone,
        my loved one,
        Knows well my malady.

        If we can understand and feel the message, then MS are transferable. I wonder what you think about this approach. Thank you.


      • Marianne says:

        Hi Safwan,

        I completely accept that mental states can be transferred from writer to reader in poetry (or indeed any other form of writing. But this doesn’t disprove physicalism, It just tells us that we can share thoughts.Physical bodies are essential to the sharing of thoughts, but so (of course) are mental states.

        Sorry it has taken me so long to answer – the academic year came in with a bang!


  7. Karel says:

    Can I also attack the third premise by saying that when A = B, is it a numerical identity?

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