What is the relationship between the mind and the body, and does substance dualism survive its objections?
substance dualism and the mind-body problem, including Descartes' arguments and the problem of interaction
A VCE Philosophy Unit 3 answer on substance dualism and the mind-body problem. Sets out Descartes' conceivability and divisibility arguments, explains the interaction problem raised by Princess Elisabeth, and evaluates dualism against physicalist alternatives.
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What this dot point is asking
VCAA wants you to explain the mind-body problem and the substance dualist answer to it, reconstruct Descartes' arguments for dualism as valid argument forms, and then evaluate dualism against its main objection (interaction) and its main rival (physicalism). You must do more than describe positions. The marks at the top of the band go to students who set out an argument premise by premise, identify exactly which premise an objection targets, and reach a defensible judgement.
The mind-body problem
The mind-body problem asks how mental states (thoughts, sensations, beliefs) relate to physical states (brain processes, behaviour). Mental states seem to have features physical states lack: they are subjective, they are about things (intentionality), and they have a felt quality. Physical states are public, located in space, and governed by physical law. The problem is to say what the relation between the two is without denying either that the mind is real or that the physical world is causally closed.
Descartes' substance dualism
René Descartes, in the Meditations on First Philosophy, defends substance dualism: there are two kinds of substance, res cogitans (thinking, non-extended) and res extensa (extended, non-thinking). The mind is identical to the thinking substance and is really distinct from the body.
The conceivability (or modal) argument
Reconstructed:
- I can clearly and distinctly conceive of myself existing without a body (as a purely thinking thing).
- Whatever I can clearly and distinctly conceive is possible (God could bring it about).
- So it is possible for my mind to exist without my body.
- If two things can exist apart, they are really distinct.
- Therefore the mind is really distinct from the body.
The divisibility argument
- The body is divisible (it has parts and is extended in space).
- The mind is indivisible (when I introspect, I find no parts).
- If two things have different properties, they are not identical (Leibniz's Law).
- Therefore the mind is not identical to the body.
The main objection: interaction
Princess Elisabeth of Bohemia, in correspondence with Descartes, pressed the decisive objection. Mind and body clearly interact: a decision (mental) raises an arm (physical), and a pinprick (physical) causes pain (mental). But causation, on the physics of the day, works by contact and motion between extended things. A non-extended substance has no surface, no location, and no way to push. So how can the mind move the body? Descartes' gesture at the pineal gland only relocates the problem; it does not explain how the immaterial acts on the material. This is the interaction problem, and it remains the strongest single objection to substance dualism.
A related worry is the causal closure of the physical: physics tells us every physical event has a sufficient physical cause. If the mind also causes physical events, either it is doing nothing extra (epiphenomenalism) or it overdetermines the effect or it violates closure. Dualists must reject or qualify closure, which is a heavy cost.
Evaluation
The conceivability argument is valid but premise 2 is contested. Conceivability may track only what we can imagine without contradiction, not genuine metaphysical possibility. The masked-man objection shows that reasoning from how things appear under a description (I can conceive my mind without my body) to a real distinction is risky: I can conceive water without conceiving H2O, yet water is H2O. The divisibility argument is vulnerable at premise 2: split-brain cases and the unity of consciousness breaking down under brain injury suggest the mind may not be as indivisible as introspection reports.
Against this, dualism has genuine explanatory virtues. It takes consciousness seriously rather than explaining it away, and it accounts for the apparent privacy and subjectivity of experience. Physicalism, its rival, avoids the interaction problem by identifying mental states with brain states, but it inherits the explanatory gap (Joseph Levine) and the hard problem of consciousness (David Chalmers): even a complete physical description seems to leave out what experience is like. So neither side is cost-free.
Judgement: substance dualism is internally coherent and captures real features of mind, but its commitment to non-physical causation sits badly with the causal closure of physics, and that cost is heavier than the explanatory gap that troubles physicalism. The interaction problem is not decisive on its own, but combined with the weakness of premise 2 in both arguments, the balance favours a physicalist or property-dualist account over substance dualism.
Exam-style practice questions
Practice questions written in the style of VCAA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
2023 VCAA3 marksHow does doubt lead Descartes to dualism?Show worked answer →
Three marks reward tracing the path from the method of doubt to the real distinction of mind and body.
The method of doubt. Descartes resolves to reject anything that can be doubted. The senses sometimes deceive, dreams are indistinguishable from waking, and an evil demon could be deceiving him about the external world and even mathematics. So the existence of his body and the whole physical world can be doubted.
The one thing that survives. Even a deceiving demon cannot make Descartes doubt that he is thinking, and so that he exists as a thinking thing (the cogito). His existence as a mind is indubitable in a way the body is not.
From doubt to dualism. Because he can clearly and distinctly conceive of himself existing as a thinking thing while doubting that any body exists, the mind and the body have different properties (one indubitable, one doubtable). By Leibniz's Law the mind is therefore really distinct from the body. Doubt thus exposes a difference that grounds substance dualism.
2021 VCAA2 marksOutline one reason why Descartes believes he is not his body.Show worked answer →
For 2 marks, give one clearly stated Cartesian reason, correctly explained.
One reason is the conceivability (real distinction) argument: Descartes can clearly and distinctly conceive of himself existing as a purely thinking thing without any body. Whatever can be clearly and distinctly conceived is possible (God could bring it about), so it is possible for his mind to exist without his body. Things that can exist apart are really distinct, so he is not identical to his body.
An acceptable alternative is the divisibility argument: the body is extended and divisible into parts, but the mind, known through introspection, has no parts and is indivisible. Since they have different properties they cannot be one and the same thing. Either reason, properly drawn out, earns full marks.
2020 VCAA2 marksHow does Descartes argue for the conclusion that he is distinct from his body?Show worked answer →
Two marks for reconstructing one of Descartes' arguments as a short valid inference.
State the conceivability argument: Descartes clearly and distinctly perceives that he can exist as a thinking, non-extended thing while doubting that his body exists. What is clearly and distinctly conceivable is metaphysically possible, so it is possible for the mind to exist without the body. Two things that can exist independently are really distinct, therefore the mind is distinct from the body.
Full marks require both the premise (clear and distinct conception of mind without body) and the move to a real distinction, not merely the assertion that mind and body differ.