Is Dualism a Convincing Theory of the Mind?
The best argument for substance dualism (the conceivability argument) fails, the best argument for property dualism (the knowledge argument) also fails, and the causal exclusion problem then shows the irreducibility claim common to both forms to be not just unsupported but fatally flawed. Dualism is not a convincing theory of the mind.
- Dualism holds that the mental is not reducible to the physical. Substance dualism — Descartes' version — holds that mind and body are distinct substances: res cogitans and res extensa. Property dualism holds there is only one kind of substance, physical matter, but that it possesses two distinct kinds of properties: physical and mental - The intuition driving both is the same: there is something about conscious experience — its first-person, subjective character — that resists physical description. I will argue that the best argument for substance dualism (the conceivability argument) fails, that the best argument for property dualism (the knowledge argument) also fails, and that the causal exclusion problem then shows the irreducibility claim common to both forms to be not just unsupported but fatally flawed. Dualism is not a convincing theory of the mind
Section 1: The Conceivability Argument and the Failure of Substance Dualism
Descartes: The Conceivability Argument
- Descartes offers two arguments for substance dualism — the indivisibility argument and the conceivability argument. The conceivability argument is the stronger of the two: its key premise, that we can conceive of mind and body being distinct, is far more plausible than the indivisibility argument's claim that the mind cannot be divided into parts. The indivisibility argument is empirically questionable given that mental functions are distributed across brain regions, and at best shows the mind behaves differently from matter, not that it is a distinct substance. The conceivability argument is substance dualism's best case - The argument runs as follows: - P1. I can conceive of my mind/myself existing without my extended physical body existing - P2. Anything that I can clearly and distinctly conceive of is metaphysically possible (since God could 'make it so') - C1. Therefore my mind existing without my extended physical body is metaphysically possible - P3. If it is metaphysically possible for X to exist without Y, then X is not identical to Y - C2. Therefore my mind is not identical with my extended physical body, nor with any part of the physical world
: The Water/H2O Objection
- The immediate objection — that possibility does not entail actuality — can be deflected by P3. But a deeper objection shows the argument proves too much, attacking P2. If conceivability establishes distinctness, the same reasoning would show that water is not H2O. We can conceive of a world where water is not H2O just as readily as we can conceive of a world with minds but no brains — yet water is H2O. The conceivability argument must go wrong somewhere - Descartes might reply that once we properly understand what water is, we cannot coherently conceive of it without H2O. But this reply is equally available to the physicalist: once we properly understand how the brain works, we may find that minds cannot exist without brains either. Unless Descartes can show a principled asymmetry between the two cases — and he cannot — the conceivability argument fails
Section 2: The Knowledge Argument and the Case for Property Dualism
Jackson: The Knowledge Argument
- Property dualism holds that mental properties — particularly qualia, the subjective character of experience — are genuinely distinct from physical properties and irreducible to them. The strongest argument for this is Frank Jackson's knowledge argument - Mary is a neuroscientist who has lived her entire life in a black and white room. She knows every physical fact about colour vision — every wavelength, every neural firing pattern, every physical process involved in seeing red. When she leaves the room and sees red for the first time, she learns something new: what it is like to see red - If Mary knew all the physical facts yet still learned something new, then what she learned cannot be a physical fact. There are therefore non-physical facts — facts about qualia — and property dualism is true
Chalmers: The Hard Problem (Independent Support)
- The knowledge argument gains further philosophical depth from Chalmers' hard problem. Even a complete physical explanation of the brain — every neuron, every process, every function — would leave unexplained why those processes are accompanied by subjective experience at all. Why is there something it is like to be in those states? The explanatory gap between physical processes and conscious experience suggests that qualia are not simply identical to physical properties — they are something over and above them
: New Knowledge of an Old Fact (Two Modes of Presentation)
- The physicalist concedes Mary gains new knowledge when she sees red, but denies she learns a new fact — she gains new knowledge of an old fact - The underlying principle: one and the same fact can be known under different modes of presentation, so coming to know a new proposition is not the same as coming to know a new fact - Illustration: someone can know 'Superman is brave' yet not know 'Clark Kent is brave,' and learn the latter as a genuine discovery — but there is only one fact (one brave man), known under two modes - Applied to Mary: in the black-and-white room she knows the physical facts of colour vision under a third-person, descriptive mode (wavelengths, neuroscience); on seeing red she comes to know one of those same physical facts under a first-person, experiential mode
Section 3: Causal Exclusion and the Cost of Irreducibility
: The Causal Problem (General)
- This is the most crucial objection because it does not merely undermine arguments for dualism — it gives a positive reason to think dualism is false. Both substance and property dualism face versions of it, but the property dualist's version is more precise and more damaging - The physical world appears causally closed: every physical event has a sufficient physical cause. When I feel pain and grimace, the grimace has a complete physical explanation in terms of neural firing patterns. If my pain is an immaterial substance or an irreducible non-physical property, it seems causally redundant — the physical explanation is already complete without it
Kim: The Causal Exclusion Argument
- Jaegwon Kim refines this as the causal exclusion argument. Given physical causal closure, mental properties are redundant because the physical explanation is already complete without them. If mental properties are genuinely distinct from physical properties, there are only two options: either mental properties are causally efficacious — in which case they overdetermine physical effects alongside their physical causes, which is implausible (it would mean every action has two complete sufficient causes, the kind of systematic coincidence we reject everywhere else) — or mental properties are causally redundant, doing no causal work at all - The second horn forces property dualists into epiphenomenalism: the view that mental properties are causally inert byproducts of physical processes, like the shadow of a moving object. The grimace is caused entirely by neural firing; the painfulness of the pain does nothing
: Why Epiphenomenalism Fails
- The purpose of epiphenomenalism is to maintain the existence of qualia in light of objections to property dualism. However, on epiphenomenalism we could never verify that qualia exist — neither from the outside nor from the inside — and so the theory has no independent grounding - From the outside, qualia are causally inert, so they leave no physical trace; there is no scientific means of detecting them - From the inside, the epiphenomenalist cannot fall back on directly experiencing their own qualia, because every mental state is causally inert and caused only by the physical: a past experience of a quale can have no effect on any later mental state, so no later belief or memory could have been caused by it - The epiphenomenalist therefore has no route — third- or first-person — to knowledge of the very qualia the theory posits. A theory of qualia that undermines all knowledge of qualia fails on its own terms
- The conceivability argument fails and the knowledge argument fails. Chalmers' hard problem provides residual motivation for irreducibility — the explanatory gap is real — but Kim's causal exclusion argument shows that the irreducibility the hard problem motivates is precisely what generates the fatal problem. Property dualism must choose between reducing mental properties to physical ones — abandoning irreducibility and becoming physicalism, which is Kim's own conclusion — or accepting epiphenomenalism, which is indistinguishable from eliminativism - One might conclude that dualism is partially convincing — that the hard problem identifies a genuine explanatory gap even if dualism cannot solve it. This partial verdict is available: Chalmers himself accepts the hard problem while acknowledging the causal difficulties. But a theory that cannot account for the causal efficacy of the very properties it posits has failed at its primary task. Dualism is not a convincing theory of the mind