The Mind-Body Problem Stated
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You stub your toe. One account of what happened involves damage at the site, signals travelling up the leg, and a pattern of activity in several regions of the brain. Another account is that it hurt.
Each account seems complete on its own terms. The first can be extended indefinitely without ever mentioning how anything felt. The second is available to you with no knowledge of nerves at all. Saying how the two accounts are related to each other has turned out to be one of the hardest things anyone has tried to say.
The problem is a conflict
Definition
Mind-body problem
The problem of saying how mental states and processes are related to physical states and processes, and in particular to the body and the brain.
Stated that way it sounds like an open question waiting on evidence. It is worse than that. The difficulty is that several claims are individually hard to deny and cannot all be true together.
The first is that mental states are real and have the features they appear to have. Pain hurts. A belief is about something. Whatever the correct theory turns out to be, it has to make room for these.
The second is that those features look unlike physical features. A pattern of neural firing has a location, a duration, a rate, and a chemistry. It is not obvious that it has any of the properties the pain seemed to have, and there is no accepted account of how a description in the first vocabulary could add up to a description in the second.
The third is that the mental and the physical affect each other constantly. The pain makes you pull your foot back, which is a physical event with a mass of tissue moving through space. Alcohol changes your mood, and a blow to the head can remove your memories. Traffic runs in both directions and nobody disputes it.
The fourth is that the physical world appears to be causally self-contained. Every physical event that has a cause seems to have a sufficient physical cause, and physiology can trace the muscle contraction back through the motor neurons without needing to cite anything non-physical.
Hold all four and you have a contradiction rather than a puzzle. The third and fourth together suggest the mental has to be physical, in some sense of that word, or else it is causally idle. The first and second together resist saying that it is. Every position in the field is a way of rejecting or reinterpreting one of the four, and each such move has a cost that its rivals are happy to point out.
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Two kinds of thing
Definition
Dualism
The view that the mental and the physical are fundamentally different in kind, so that mental phenomena are not reducible to, or identical with, anything physical.
The best-known statement is Descartes's. In the Meditations on First Philosophy of 1641 he argued that he could clearly and distinctly conceive of his mind existing without his body and of his body existing without his mind, that whatever can be clearly and distinctly conceived is within God's power to bring about, and therefore that mind and body can exist apart and are really distinct. Thought is what a mind essentially is; extension in space is what a body essentially is; and nothing has both essences.
The objection that has followed the view ever since was put to Descartes in his own lifetime. Princess Elisabeth of Bohemia began corresponding with him in 1643 and asked how an unextended thinking substance could move a body at all. The causal explanations of the new physics worked by contact between extended things, and a mind with no extension has no way of entering into an explanation of that shape. Descartes's replies did not satisfy her, and most readers since have agreed that they did not satisfy the question.
Dualism comes in more than one strength. A version can hold that minds are distinct substances, capable in principle of existing on their own, or it can hold that there is only one kind of thing in the world while insisting that some of its properties are not physical properties. The intermediate tier separates these carefully, along with the several positions available about what a non-physical mind could be doing causally. What matters at this stage is the shared commitment: something about the mental resists absorption into the physical story.
One kind of thing
Definition
Monism
The view that reality is composed of one fundamental kind of thing, so that mental and physical phenomena are not two basic categories but aspects, arrangements, or instances of a single category.
Monism is a genus rather than a position, since it leaves open what the one kind is. An idealist takes it to be mental and treats the physical world as constructed out of experience. Another line takes the fundamental kind to be neither mental nor physical, with both emerging from something more basic, and the advanced tier examines what such a view would have to look like. The version that dominates contemporary work takes the one kind to be physical.
Definition
Physicalism
The view that everything is physical: that the world contains nothing over and above what a completed physics would describe, so that mental states and processes are either identical with physical ones or wholly fixed by them.
The word materialism means much the same thing in current usage and the two are often used interchangeably. The older term is tied to matter in a sense that stopped being adequate once physics started quantifying over fields and forces, which is part of why the newer one displaced it.
Physicalism is a majority view among philosophers of mind, and its appeal is that it dissolves the interaction difficulty at a stroke. If the pain is a physical state, there is no mystery about how it moves your foot. The debt it takes on is the second of the four claims above. It owes an account of how a physical state could be the hurting, and the whole apparatus of the intermediate and advanced tiers is either an attempt to pay that debt or an argument that it cannot be paid.
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Why the neuroscience does not settle it
A natural thought is that the problem is a historical curiosity that the brain sciences have overtaken. The evidence for dependence is overwhelming: lesions remove capacities, drugs alter experience, and imaging finds reliable correlations between reported states and measured activity.
Everyone in the debate accepts that evidence and has accepted it for a long time. What it establishes is that mental states depend on brain states in a systematic way, and the disputed question is what that dependence amounts to. Correlation between two things is consistent with their being identical, and it is also consistent with their being distinct but reliably linked. A dualist of the second kind above predicts the same imaging results as a physicalist, and predicts them for a different reason.
That is what makes this a philosophical problem rather than an empirical one at this stage. The disagreement is not about what happens in the brain when someone is in pain. It is about what would have to be true for a description of that activity to be a description of the pain, and no measurement answers that on its own.
Objection
The problem is an artefact of a bad picture. Descartes bequeathed the image of a mind lodged inside a body like a pilot in a vessel, and once that image is in place the question of how the two communicate becomes unanswerable. But the image was never earned. Mental terms are not names for inner objects; they describe what people do and are disposed to do. Talk of beliefs and pains is a way of characterising a whole living animal, not a report about a hidden compartment. Drop the picture and the problem goes with it.
Reply
The criticism is Gilbert Ryle's, and the phrase he used for the picture, the ghost in the machine, has outlasted most of the philosophy of its decade. Against the picture it targets, it lands.
Two things limit it as a dissolution of the problem.
The first is that the problem does not depend on the picture. It can be stated without any inner compartment at all, as the four claims above were stated, in terms of properties rather than places. There is something it is like to be in pain, and that fact needs accommodating whether the pain is located in a private theatre or nowhere in particular. Removing the theatre leaves the question of what to do with the feature.
The second is that the positive proposal has been tested and found wanting. The view that mental terms are wholly analysable into behaviour and behavioural dispositions was developed carefully in the middle of the last century and abandoned, mainly because the analyses could not be completed: what a person does when they want something depends on what they believe, and what they do when they believe something depends on what they want, so neither can be cashed out in purely behavioural terms without the other. The intermediate tier follows that failure and what replaced it.
The problem also predates Descartes by a long way and has been stated in traditions with no exposure to him, which is some evidence that it is not the residue of one man's diagram.
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What comes next
The problem has been stated as though the mental were a single thing. It is not. Believing that Ottawa is in Canada and feeling a toothache are both mental, and they raise difficulties of different sizes. Separating them is the first real progress the subject makes, and it is the next article's business.
Further reading
- René Descartes, Meditations on First Philosophy (1641), the Sixth Meditation, for the argument that mind and body are really distinct.
- The correspondence between Descartes and Elisabeth of Bohemia, beginning in 1643, for the interaction objection in its original form.
- Gilbert Ryle, The Concept of Mind (1949), chapter 1, for the charge that the problem rests on a category mistake.
- Stanford Encyclopedia of Philosophy, "Dualism".
- Stanford Encyclopedia of Philosophy, "Physicalism", for Hempel's dilemma and the responses to it.
- Stanford Encyclopedia of Philosophy, "Elisabeth, Princess of Bohemia", by Lisa Shapiro.
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