Dualist theories of mind

Substance dualism: Descartes' arguments#

StandardAQA 7172 3.4 Metaphysics of mind — DualismDfE GCE Philosophy subject content

Substance and property dualism

Fig. 1Substance dualism posits two substances; property dualism, one substance with two kinds of property.

Substance dualism holds that mind and body are two distinct KINDS of substance: the mind (or soul) is a non-physical, thinking, unextended substance (res cogitans), and the body is a physical, extended, non-thinking substance (res extensa). Crucially, because they are distinct substances, the mind CAN exist without the body — it is not dependent on the body for its existence — which underwrites the possibility of an afterlife and of personal survival of bodily death. Descartes is the classic proponent, and he offers two main arguments for the real distinction between mind and body: the conceivability (or indivisibility-and-doubt) argument and the divisibility argument.

The CONCEIVABILITY argument (Meditation VI) runs: I can clearly and distinctly conceive of myself (a thinking thing) existing WITHOUT my body — I can conceive of being a disembodied mind. Whatever I can clearly and distinctly conceive is metaphysically possible (God could bring it about). So it is possible for my mind to exist without my body. But if mind and body were identical (one thing), it would be impossible for one to exist without the other (a thing cannot exist without itself). Therefore mind and body are not identical — they are really distinct. The argument turns on the inference from CONCEIVABILITY to POSSIBILITY, and on Leibniz's Law (identical things share all properties, so if mind and body differ in a property — separability — they are not identical).

The DIVISIBILITY (indivisibility) argument (Meditation VI) uses Leibniz's Law directly: the body, being extended, is divisible — it has parts and can be divided (a limb can be removed). But the mind is INDIVISIBLE — it has no parts; when I introspect, I cannot conceive of half a mind, and the mind is experienced as a unity. So the mind has a property (indivisibility) that the body lacks (the body is divisible). By Leibniz's Law (things with different properties are not identical), the mind and the body are not identical — they are distinct substances. The argument's premise is that the mind is genuinely indivisible, which physicalists dispute (split-brain cases, and the divisibility of mental functions across brain regions, suggest the mind may not be the simple unity Descartes assumed).

Descartes also argues from DOUBT (the cogito context): I cannot doubt that I (a thinking thing) exist, but I CAN doubt that my body exists (the demon might deceive me about the physical world); so my mind has a property (indubitable existence) my body lacks, hence they differ. This 'argument from doubt' is generally regarded as fallacious because it commits the MASKED MAN fallacy: it reasons within an intensional (doubt) context, where substitution of co-referring terms fails. Compare: 'I can doubt that the masked man is my father' does not show the masked man is not my father — my epistemic states (what I can doubt) do not track the real properties of the thing. So the fact that I can doubt my body's existence but not my mind's shows something about my knowledge, not about whether mind and body are distinct. This is a standard objection, and it also threatens the conceivability argument (does conceivability track real possibility, or only my epistemic limitations?), as the evaluation section develops.

Worked example

The masked-man fallacy in the argument from doubt

Explain why Descartes' argument from doubt commits the masked-man fallacy.

The argument
I cannot doubt my mind exists, but I can doubt my body exists; so mind and body differ in a property, hence are distinct.
The parallel
I can doubt the masked man is my father, but I cannot doubt my father is my father; yet the masked man IS my father.
The diagnosis
'Being doubted by me' is an intensional property that does not track real identity; substitution of co-referring terms fails in doubt contexts.
The upshot
So facts about what I can doubt reveal my epistemic state, not the real distinctness of mind and body; the argument is invalid.

Result: The argument from doubt fails by the masked-man fallacy: it infers a real distinction from an intensional (epistemic) difference, which does not track identity — and the same worry (does conceivability track possibility?) shadows Descartes' better arguments.

Typical mistakes

Treating substance dualism as merely 'the mind and body are different'; it is the strong claim that they are distinct SUBSTANCES, so the mind CAN exist without the body.
Presenting the argument from doubt as sound; it commits the masked-man fallacy (reasoning from what one can doubt to what is really identical), and even Descartes' better arguments face the conceivability-possibility worry.

Active revision

Outline Descartes' conceivability argument for substance dualism. (5-mark AO1 response)

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for philosophy (Department for Education)

Property dualism#

StandardAQA 7172 3.4 Metaphysics of mind — DualismDfE GCE Philosophy subject content

Epiphenomenalism

Fig. 2If the physical is causally closed, non-physical mental properties seem to be causally idle by-products.

Property dualism is a more modest dualism than Descartes'. It agrees with physicalism that there is only ONE kind of SUBSTANCE — the physical — so it does not posit an immaterial soul; but it holds that this physical substance (the brain) has TWO fundamentally different kinds of PROPERTY: physical properties (mass, charge, neural firing) and mental properties (qualia, the felt character of experience) that are NON-PHYSICAL and IRREDUCIBLE — not identical to, and not explicable in terms of, any physical property. On this view the mind is not a separate thing, but consciousness involves genuine, non-physical properties of the brain.

Property dualism is motivated by the difficulty physicalism has with qualia (the hard problem). Even granting that the brain is the seat of the mind, it seems we can give a complete physical account of the brain and still leave out the felt quality of experience — the redness of red, the painfulness of pain. If these phenomenal properties are real and are not captured by any physical description, then they are non-physical properties, and property dualism is true. The knowledge argument and the zombie argument (next sections) are precisely arguments FOR property dualism: they aim to show that no amount of physical information captures the phenomenal properties, so those properties are additional to the physical facts.

Property dualists hold that mental properties SUPERVENE on physical properties: there can be no change in mental properties without a change in physical properties (fix the physical facts and you fix the mental), so the mental depends on the physical — but is not reducible to it. This distinguishes property dualism from substance dualism (no separate soul; mind depends on the brain, so no straightforward afterlife) and from physicalism (the mental properties are non-physical and irreducible). It is a 'non-reductive' view: mental properties are real, dependent on the physical, but over and above the physical properties.

The main difficulty for property dualism is mental causation, in the form of EPIPHENOMENALISM. If the physical world is causally closed (every physical event has a sufficient physical cause), and mental properties are non-physical, then it seems mental properties cannot cause physical events — my brain state causes my behaviour, and the non-physical quale rides along as a causally IDLE by-product (an 'epiphenomenon'), like the whistle on a steam train that makes no difference to its motion. Epiphenomenalism is deeply counterintuitive (surely my PAIN causes me to cry out; surely my experience of red is why I say 'red') and self-undermining worries arise (if qualia are causally idle, how do we even come to talk and think about them, or know about them?). Property dualists respond either by biting the bullet (accepting epiphenomenalism — Jackson originally did), or by denying causal closure, or by adopting 'non-reductive physicalism' that allows mental properties a causal role through their physical realisers — but each response has costs. Evaluation weighs whether property dualism successfully captures the reality of qualia (its motivation) without either collapsing into physicalism (if mental properties do causal work only via their physical bases, are they really distinct?) or into an implausible epiphenomenalism (if they do no causal work, they seem idle and unknowable). This tension — between the reality of qualia and their causal efficacy — is property dualism's central problem, and the reason many philosophers seek a physicalist or functionalist account that avoids it.

Worked example

The epiphenomenalism dilemma

Explain why causal closure forces property dualism towards epiphenomenalism, and one response.

Causal closure
Every physical event has a sufficient PHYSICAL cause (physics is complete).
The squeeze
My behaviour (a physical event) already has a sufficient physical cause (a brain state), leaving no causal work for a non-physical quale.
The conclusion
So the non-physical mental property is causally idle — an epiphenomenon that makes no difference to behaviour.
A response
Deny causal closure, or hold mental properties are causally efficacious via their physical realisers (non-reductive physicalism) — but the first conflicts with physics, the second risks collapsing the distinctness of mental properties.

Result: Causal closure pushes property dualism to epiphenomenalism, which is counterintuitive and arguably self-undermining; the escapes (denying closure, or realiser-causation) each threaten either physics or the very distinctness that motivates the view.

Typical mistakes

Confusing property dualism with substance dualism; property dualism posits NO separate soul — only irreducible mental PROPERTIES of the physical brain, so no straightforward afterlife.
Overlooking epiphenomenalism; the causal idleness of non-physical mental properties (given causal closure) is the main objection and must be addressed.

Active revision

'Property dualism cannot explain how the mind affects the body.' Assess this claim. (25-mark essay)

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for philosophy (Department for Education)

The knowledge argument (Mary)#

AdvancedAQA 7172 3.4 Metaphysics of mind — DualismDfE GCE Philosophy subject content

The knowledge argument (Mary)

Fig. 3Mary knows all physical facts but learns something new on seeing red, so not all facts are physical.

Frank Jackson's knowledge argument ('Epiphenomenal Qualia', 1982) is one of the two great arguments against physicalism about qualia. Its thought-experiment: Mary is a brilliant scientist who has lived her whole life in a black-and-white room, learning about the world through a black-and-white monitor. She learns ALL the physical facts about colour vision — the wavelengths of light, the physiology of the retina and visual cortex, the complete neuroscience of colour experience. Mary knows everything physical there is to know about seeing red. Then one day she leaves the room and sees a red rose for the first time.

The argument runs: (P1) before leaving, Mary knew all the PHYSICAL facts about colour vision. (P2) When she leaves and sees red, she LEARNS something new — she learns what it is LIKE to see red (she gains new knowledge, 'so THAT is what red looks like'). (P3) So there is a fact she did not know before — the phenomenal fact about the quale of red — even though she knew all the physical facts. Therefore (C) there are non-physical facts (facts about qualia) that are not included in the physical facts, so physicalism is false. In brief: Mary knew all the physical facts but did not know all the facts (she did not know what red is like), so not all facts are physical facts.

The argument's power is that it isolates the qualia problem sharply: it grants the physicalist EVERYTHING physical and still seems to show something is left out — the subjective, phenomenal character of experience. If Mary genuinely learns a new FACT on seeing red, and she already knew every physical fact, then the phenomenal fact is a further, non-physical fact, and physicalism (the thesis that all facts are physical) is false. The argument thus supports property dualism (there are non-physical properties/facts, the qualia), and it connects to Nagel's bat and to Chalmers' zombies as variations on the theme that the physical facts do not entail the phenomenal facts.

Physicalists have three main replies, which the specification requires. (1) The ABILITY reply (Lewis, Nemirow): Mary gains not new propositional KNOWLEDGE-THAT but new ABILITIES (know-how) — she gains the ability to imagine, recognise and remember red. Since she learns a new skill, not a new fact, no new non-physical fact is required, and physicalism is safe. (2) The ACQUAINTANCE reply: Mary gains new acquaintance knowledge — she becomes directly acquainted with the experience of red for the first time — but acquaintance with a fact is not the same as knowing a new fact; she knew the fact under a physical description and now knows the SAME fact by acquaintance. (3) The NEW-KNOWLEDGE/OLD-FACT reply (the 'phenomenal concepts' strategy, Loar, Tye): Mary gains new knowledge of an OLD (physical) fact under a new MODE OF PRESENTATION — she already knew the physical fact (the brain state) under a physical concept, and now knows the SAME fact under a phenomenal concept ('THIS experience'). Since she learns a new WAY of grasping an old fact, not a new fact, no non-physical fact exists — just as learning that Hesperus is Phosphorus is learning an old fact (one planet) under two modes of presentation. Evaluation weighs these: the ability reply is challenged by the point that Mary plainly seems to learn a new TRUTH ('red looks like THIS'), not just a skill; the acquaintance and old-fact replies are more resilient but must explain how a single fact can be grasped in a way that generates a genuine sense of NEW information without there being a new fact — the 'phenomenal concepts strategy' is the leading physicalist response, and whether it succeeds (whether phenomenal concepts pick out purely physical facts) is the crux. A balanced verdict is that the knowledge argument makes a powerful prima facie case that physicalism leaves out the phenomenal, but that the new-knowledge/old-fact reply gives the physicalist a serious answer, so the argument is not decisive — its force turns on whether what Mary gains is a new FACT or a new way of grasping an old one.

Worked example

The new-knowledge/old-fact reply

Explain the new-knowledge/old-fact reply to the knowledge argument, using the Hesperus/Phosphorus analogy.

The challenge
Mary knew all physical facts, yet learns something on seeing red — apparently a new, non-physical fact.
The reply
She learns an OLD (physical) fact under a NEW mode of presentation: she knew the brain-state fact under a physical concept, now grasps the SAME fact under a phenomenal concept ('THIS').
The analogy
Learning that Hesperus is Phosphorus is learning about ONE planet under two names — new knowledge, old fact; no new object.
The assessment
This preserves physicalism (no new fact), but must show phenomenal concepts really pick out PHYSICAL facts — the disputed 'phenomenal concepts strategy'.

Result: The new-knowledge/old-fact reply lets the physicalist grant that Mary gains something (a new mode of presentation) while denying a new fact — the strongest reply, though it depends on the contested claim that phenomenal concepts refer to purely physical facts.

Typical mistakes

Stating that Mary learns 'more physics'; the argument stipulates she already knows ALL physical facts — what she gains on seeing red is the disputed point (a new fact, or a new ability/mode of presentation?).
Giving only one physicalist reply; the specification expects the ability, acquaintance and new-knowledge/old-fact replies, with evaluation of each.

Active revision

'The knowledge argument proves that physicalism is false.' Is this claim true? Defend your answer. (25-mark essay)

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for philosophy (Department for Education)

The zombie/conceivability argument#

AdvancedAQA 7172 3.4 Metaphysics of mind — DualismDfE GCE Philosophy subject content

The zombie argument

Fig. 4If a physical duplicate could lack consciousness, then consciousness is not fixed by the physical, so physicalism is false.

The philosophical zombie argument, developed by David Chalmers (The Conscious Mind, 1996), is the second great anti-physicalist argument. A philosophical ZOMBIE is a being physically and functionally IDENTICAL to a normal conscious human — same brain, same behaviour, same functional organisation — but WITHOUT any conscious experience: 'all dark inside', with no qualia. It processes information, says 'ouch' when injured, and behaves exactly like us, but there is NOTHING it is like to be it. The argument is a conceivability argument about the relation between the physical and the phenomenal.

The argument runs: (P1) philosophical zombies are CONCEIVABLE — we can coherently conceive of a being physically identical to me but lacking consciousness. (P2) What is conceivable (in the relevant, ideal sense) is metaphysically POSSIBLE — so zombies are metaphysically possible (there is a possible world physically identical to ours but lacking consciousness). (P3) If physicalism were true, then fixing all the physical facts would fix all the facts, including the facts about consciousness — so a physical duplicate of our world could not lack consciousness; zombies would be IMPOSSIBLE. Therefore (C) since zombies are possible, physicalism is false: consciousness does not logically supervene on the physical, so the phenomenal facts are further facts over and above the physical.

The argument's structure mirrors the knowledge argument but from the side of possibility rather than knowledge: where Mary shows the physical facts do not give us all the KNOWLEDGE, zombies show the physical facts do not fix all the FACTS (a physical duplicate could differ in consciousness). Both aim to show that consciousness is not entailed by the physical, supporting property dualism (and Chalmers' 'naturalistic dualism', on which consciousness is a further fundamental feature of the world). The argument is often paired with the 'inverted qualia' possibility (a duplicate with SYSTEMATICALLY inverted colour experiences), which makes a related point about functional/physical states failing to fix qualia.

The central objection targets the inference from CONCEIVABILITY to POSSIBILITY (P2). Physicalists (notably Dennett, and the 'type-B' physicalists) argue that our ability to conceive of zombies does not establish that they are genuinely possible — conceivability is a guide to possibility only when our concepts are complete and we are not misled. Kripke's cases (water = H2O, necessary a posteriori) show that some things seem conceivable (water not being H2O) but are impossible; likewise, if consciousness IS a physical process, then a physical duplicate WOULD be conscious, and our sense that we can conceive a zombie merely reflects our incomplete grasp of how the physical constitutes the phenomenal. Dennett goes further, arguing zombies are NOT really conceivable at all (a being functionally identical to us would have to have whatever consciousness amounts to), and that the intuition trades on smuggling in a dualist picture of qualia as an inessential extra. Chalmers replies with a two-dimensional semantics designed to show that, for consciousness specifically, conceivability DOES entail possibility (there is no gap between how consciousness appears and what it is, unlike water). Evaluation weighs this: the zombie argument, like the knowledge argument, makes a powerful case that the physical does not obviously ENTAIL the phenomenal (the explanatory gap is real), but its move from conceivability to metaphysical possibility is exactly where physicalists resist, invoking Kripke and the phenomenal-concepts strategy; so the argument is not decisive, and the debate turns on whether conceivability is a reliable guide to possibility in the special case of consciousness. A balanced verdict is that the zombie and knowledge arguments together establish a robust EXPLANATORY gap — physical accounts do not transparently explain WHY there is experience — but that whether this gap is merely EPISTEMIC (a limit on our understanding, compatible with physicalism) or ONTOLOGICAL (a real gap in the world, refuting physicalism) is precisely what remains contested.

Worked example

The conceivability-possibility objection

Explain why the move from conceivability to possibility is the weak point of the zombie argument, using Kripke.

The premise
Zombies are conceivable, and (P2) what is conceivable is metaphysically possible.
Kripke's lesson
'Water is not H2O' seems conceivable, yet is impossible (water is necessarily H2O) — so conceivability can fail to track possibility (the necessary a posteriori).
Apply to zombies
If consciousness IS a physical process, a physical duplicate would be conscious, and our 'conceiving' a zombie reflects an incomplete grasp of how the physical constitutes experience.
Chalmers' reply
He argues (via two-dimensional semantics) that consciousness is special — there is no gap between how it appears and what it is — so here conceivability DOES entail possibility.

Result: The zombie argument stands or falls on the conceivability-to-possibility inference; Kripke shows it can fail, so physicalists resist, while Chalmers argues consciousness is the exception — leaving the argument powerful but not decisive.

Typical mistakes

Describing a zombie as behaviourally or physically different from us; the whole point is that it is a PERFECT physical and functional duplicate that merely lacks consciousness.
Treating conceivability as obviously entailing possibility; the Kripkean necessary a posteriori (water = H2O) shows conceivability can mislead, which is the key physicalist objection to engage.

Active revision

'The conceivability of zombies shows that consciousness is not physical.' Discuss. (25-mark essay)

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for philosophy (Department for Education)

Objections: interaction and other minds#

AdvancedAQA 7172 3.4 Metaphysics of mind — DualismDfE GCE Philosophy subject content

The interaction problem and causal closure

Fig. 5A non-physical mind causing physical events seems to violate the causal closure and conservation of the physical.

Dualism faces its own battery of objections, of which the INTERACTION problem is the most serious for substance dualism. If mind and body are radically different substances — one immaterial and unextended, the other physical and extended — how can they causally INTERACT, as they evidently do (my decision moves my arm; a pin-prick causes my pain)? Princess Elisabeth of Bohemia pressed exactly this to Descartes in their correspondence: causation, as we understand it, involves contact and the transfer of motion between physical things, but an immaterial mind has no location, size or surface to make contact with the body, so it is unintelligible how it could impart motion to it. Descartes' own answer (that interaction occurs in the pineal gland) merely relocates the problem — how does the immaterial mind move even the pineal gland? — without solving it.

The interaction problem is sharpened by the CAUSAL CLOSURE of the physical: modern physics holds that every physical event has a sufficient physical cause, and that physical quantities (energy, momentum) are conserved. If the mind is non-physical and causes physical events, then either it adds energy to the physical world (violating conservation laws and contradicting well-confirmed physics) or physical events are OVERDETERMINED (having both a sufficient physical cause and a mental cause), which is implausible, or the mind is causally idle (epiphenomenalism). So dualist interaction seems to conflict with the causal closure and conservation principles of physics — a powerful scientific objection. Historical dualists offered desperate alternatives (occasionalism: God coordinates mind and body; parallelism: they run in pre-established harmony without interacting), but these abandon genuine mental causation and are widely rejected.

The PROBLEM OF OTHER MINDS is a second objection, epistemological rather than metaphysical. If the mind is a private, non-physical substance accessible only to its owner (as substance dualism implies), how can I know that other people have minds at all? I observe only their BODIES and BEHAVIOUR, never their (private, immaterial) minds; so, on dualism, other minds are hidden behind a 'veil' of behaviour, and I cannot be certain they are not mindless automata (or zombies). Dualism thus seems to make knowledge of other minds problematic. The standard dualist reply is the ARGUMENT FROM ANALOGY: I know in my own case that certain behaviour (crying out) is caused by certain mental states (pain); others behave similarly; so by analogy their behaviour is probably caused by similar mental states. But this is an inductive inference from a SINGLE case (my own), which is a weak basis, and it is exactly the kind of inference physicalist and behaviourist theories claim to avoid (by tying the mental more closely to the behavioural or physical).

Evaluation weighs these objections against dualism's motivations. The interaction problem and causal closure are widely regarded as decisive against SUBSTANCE dualism: the conflict with conservation and closure, and the unintelligibility of immaterial-material causation, are grave, and PROPERTY dualism inherits a version (epiphenomenalism). A dualist may reply that we should not assume causation must be physical contact (Hume showed we do not really understand causal necessitation even between physical events, so mind-body causation is no worse off), and that causal closure is a methodological assumption, not a proven fact — but these replies are defensive, and most philosophers take the mental-causation problem to be dualism's fatal difficulty. The other-minds problem is serious but not unique to dualism (any view on which the mental is not simply identical to public behaviour faces some version), and the argument from analogy, or an inference to the best explanation (other minds best explain others' behaviour), offers a partial answer. A balanced verdict is that dualism's positive case (the knowledge and zombie arguments) makes a strong case that physicalism leaves out qualia, but that its negative liabilities (the interaction problem, causal closure, epiphenomenalism, other minds) are severe — which is why many philosophers seek a view that keeps dualism's respect for consciousness while avoiding its causal difficulties, and why physicalism and functionalism remain attractive despite the qualia problem.

Worked example

Causal closure against interaction

Explain how causal closure sharpens the interaction problem, and one dualist reply.

Elisabeth's problem
An immaterial, unextended mind has no way to make physical contact with the body, so it is unclear how it could move it.
Add closure
Physics holds every physical event has a sufficient physical cause and conserves energy; a non-physical cause would add energy (violating conservation) or be redundant.
The trilemma
So mental causation must either break physics, or overdetermine the effect, or be epiphenomenal — none attractive.
A dualist reply
Causal closure is a methodological assumption, not proven; and (Hume) we do not really understand physical causation either, so mind-body causation is no worse off — but these replies are defensive.

Result: Causal closure turns the interaction problem into a sharp conflict with physics, widely thought decisive against substance dualism; the dualist's replies (closure unproven; causation obscure anyway) blunt but do not remove the force.

Typical mistakes

Treating interaction as a minor puzzle; the conflict with causal closure and conservation of energy is a major, arguably decisive, scientific objection to substance dualism.
Assuming the other-minds problem is unique to dualism; it presses hardest on dualism (private immaterial minds) but any non-behaviourist view faces a version.

Active revision

'The interaction problem is fatal to substance dualism.' Is this claim true? Defend your answer. (25-mark essay)

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for philosophy (Department for Education)

Do the dualist arguments succeed?#

AdvancedAQA 7172 3.4 Metaphysics of mind — DualismDfE GCE Philosophy subject content

The explanatory gap: epistemic or ontological?

Fig. 6The dualist arguments show an explanatory gap; whether it is merely epistemic or ontological decides the debate.

A final judgement must weigh dualism's positive arguments (the knowledge and zombie arguments, and Descartes' conceivability argument) against its negative liabilities (the interaction problem, causal closure, epiphenomenalism, other minds). The positive arguments make a strong and resilient case that physical accounts do not TRANSPARENTLY explain consciousness — there is a real EXPLANATORY GAP between the physical facts and the phenomenal facts, which Nagel, Jackson and Chalmers each dramatise. This is dualism's genuine strength: it takes the reality and irreducibility of qualia seriously, where physicalism is always under pressure to explain them away.

But the positive arguments share a common vulnerability that limits their force: they all move from an EPISTEMIC premise (what we can conceive, or what Mary can know) to an ONTOLOGICAL conclusion (what is metaphysically possible, or what facts exist). The physicalist's best replies — the phenomenal-concepts strategy (against Mary) and the Kripkean denial that conceivability entails possibility (against zombies) — all target exactly this move, arguing that the explanatory gap is merely EPISTEMIC (a limit on our understanding or our concepts), not ONTOLOGICAL (a real gap in the world). If the gap is only epistemic, physicalism survives: consciousness IS physical, but our special phenomenal concepts make it seem otherwise. So the central question of the whole debate is whether the explanatory gap is epistemic or ontological — and this remains genuinely unresolved.

Substance dualism specifically is in a weak position: its positive case (Descartes' conceivability and divisibility arguments) is undermined by the masked-man/conceivability worries and by split-brain evidence against the mind's indivisibility, while its negative liabilities (the interaction problem, conflict with causal closure) are severe. PROPERTY dualism is stronger, since it drops the immaterial soul and accepts the mind's dependence on the brain, so it fits neuroscience better; but it faces epiphenomenalism (non-physical properties seem causally idle given closure), which is deeply counterintuitive and arguably self-undermining. So even a sympathetic assessment tends to favour property over substance dualism, while noting that property dualism's causal problem is real.

A defensible A-Level judgement is nuanced and states its standard. If the question is whether dualism ESTABLISHES that consciousness is non-physical, the honest verdict is that it does not: the knowledge and zombie arguments are powerful but not decisive, because the epistemic/ontological gap question is open and the physicalist has serious replies. If the question is whether dualism POSES a genuine problem for physicalism, the verdict is that it does: the explanatory gap is real, and physicalism owes an account of consciousness it has not conclusively delivered (the hard problem persists). A candidate might reasonably conclude that substance dualism is refuted (interaction, closure, indivisibility), that property dualism captures the reality of qualia but at the cost of epiphenomenalism, and that the debate between property dualism and physicalism is a stand-off over whether the explanatory gap is epistemic or ontological — with functionalism (next topic) offering a different route that some think evades the whole problem. What earns the marks is engaging the specific replies (not just asserting 'qualia prove dualism' or 'science shows physicalism'), distinguishing substance from property dualism, and defending a judgement that names its standard and the decisive open question.

The topic is the hinge of the metaphysics-of-mind unit. Its arguments (Mary, zombies) are the case AGAINST the physicalist theories of the next topic, whose replies (the phenomenal-concepts strategy, identity theory, eliminativism) are the responses; and functionalism is often presented as the view that best keeps physicalism's virtues while accommodating multiple realisability, only to face the qualia objections (absent and inverted qualia) that are the knowledge and zombie arguments in another form. The epistemology unit's rationalism/empiricism debate also reappears here: whether Mary can know what red is like a priori, from the physical facts alone, or must have the experience, is a version of the question whether all knowledge derives from experience. Consciousness — the reality and irreducibility of qualia — is the single thread running through the entire unit, and one's judgement here shapes one's assessment of every theory that follows.

Worked example

Model 25-mark plan: do the dualist arguments succeed?

Plan an essay defending a judgement on whether the arguments for dualism succeed.

Thesis
The dualist arguments show a real explanatory gap but do not prove dualism, because the epistemic/ontological gap question is open; substance dualism fails, property dualism is strained by epiphenomenalism.
AO1
Substance and property dualism; the knowledge and zombie arguments; the interaction and other-minds objections.
For dualism
Mary and zombies make a strong case that physical facts do not entail phenomenal facts — the hard problem is real.
Against
The arguments move from epistemic premises to ontological conclusions; the phenomenal-concepts and Kripkean replies keep the gap epistemic; substance dualism faces interaction/closure/indivisibility.
Judgement
Conclude that dualism poses a genuine, unrefuted problem for physicalism (the explanatory gap), but does not establish that consciousness is non-physical — the epistemic/ontological question is the unresolved crux, with functionalism a further option.

Result: A defensible judgement: the dualist arguments establish a real explanatory gap and refute substance dualism's rivals' complacency, but do not prove dualism — property dualism captures qualia at the cost of epiphenomenalism, and the epistemic/ontological status of the gap remains the open, decisive question.

Typical mistakes

Concluding 'qualia prove dualism' without engaging the phenomenal-concepts and conceivability replies; the epistemic/ontological gap question is precisely what is unresolved.
Treating substance and property dualism as equally strong; property dualism fits neuroscience better but faces epiphenomenalism, while substance dualism faces interaction and indivisibility.

Active revision

'Dualism is the best account of the mind.' Is this claim true? Defend your answer. (25-mark essay)

Active recall

Recall the key points — then reveal.

Sources: GCE AS and A level subject content for philosophy (Department for Education)

Key points

The masked-man fallacy in the argument from doubt

Key points

The epiphenomenalism dilemma

Key points

The new-knowledge/old-fact reply

Key points

The conceivability-possibility objection

Key points

Causal closure against interaction

Key points

Model 25-mark plan: do the dualist arguments succeed?

Sources

Dualist theories of mind

Key points

The masked-man fallacy in the argument from doubt

Key points

The epiphenomenalism dilemma

Key points

The new-knowledge/old-fact reply

Key points

The conceivability-possibility objection

Key points

Causal closure against interaction

Key points

Model 25-mark plan: do the dualist arguments succeed?

Sources