IB Philosophy 10.3.5 Mind–body Dualism Notes

Substance Dualism: Two Distinct Kinds of Being

1. In 10.3.2, Descartes established that the self is essentially a res cogitans (thinking thing). He now develops this into a full metaphysical doctrine (a claim about the fundamental nature of reality): the mind and the body are not merely different in the way we think about them, but are two separate substances with entirely different natures.
2. Descartes' primary argument for dualism draws on theconceivability principle. He can clearly and distinctly conceive of his mind existing without a body, and can conceive of a body existing without a mind.
   1. Since God could bring about anything that isclearly and distinctly conceivable, mind and body must bereally distinct substances.
3. Substance dualismholds that the mind (res cogitans) isnon-extended: it does not occupy space, has no shape or size, and cannot be divided into parts. The body (res extensa) is extended: it occupies space, has measurable dimensions, and isinfinitely divisible.
4. A supporting argument comes from theindivisibility of the mind. The body can be divided (one can lose a limb while remaining the same person), but the mind cannot: one cannot remove half of a thought or half of a consciousness.
   1. This asymmetry of divisibility (the fact that body can be split while mind cannot) points to a fundamental difference in kind between res cogitans and res extensa.
5. Descartes also appeals to theclarity and distinctness criterion(10.3.3). Since he has a clear and distinct idea of the mind as purely thinking and a clear and distinct idea of the body as purely extended, and since what is clearly perceived is true (guaranteed by anon-deceiving God, 10.3.4), the distinction must be real.
6. This position situates Descartes within a long tradition ofdualist thinkingin Western philosophy.Platodistinguished the immortal soul from the mortal body, and Christian theology maintained the distinction between the spiritual soul and the physical body.
   1. Descartes provides this tradition withrigorous philosophical foundations, grounding the soul-body distinction in the method of clear and distinct ideas.
7. Substance dualism connects directly to the mind-body problem discussed in Unit 1.3.2. It set the terms for nearly every debate about mind and matter since: physicalists, behaviourists, and property dualists are all responding to the problem Descartes defined, making it one of the most consequential doctrines in the history of philosophy.
8. The Cartesian view contrasts sharply with theConfucian conceptionof the person (10.2.1), which does not posit a sharp mind-body division, a contrast developed in the Comparative Perspectives section below.

The Interaction Problem

1. The most serious challenge to substance dualism is theinteraction problem. If the mind is non-extended and the body is extended, and if causal interaction requires some shared property between cause and effect, then it seemsimpossible for mind and body to affect each other.
2. Yetcausal interactionbetween mind and body appears undeniable in everyday experience. When I decide to raise my arm, my arm rises (mental cause, physical effect); when I stub my toe, I feel pain (physical cause, mental effect).
   1. Substance dualismmust explain how suchmind-body interactionsare possible given that the two substances share no common properties.
3. Princess Elisabeth of Bohemiaraised this objection in her famous 1643 correspondence with Descartes. She asked how the soul, being only a thinking substance, can determinebodily spiritsto perform voluntary actions.
   1. This remains one of the mostincisive philosophical challengesDescartes faced, and no fully satisfactory response was given.
4. Descartes' response was not entirely satisfactory. He suggested that thepineal glandserves as the point of interaction between mind and body.
   1. However, this answer merelyrelocates the problem: how does a non-extended substance interact with a small piece ofextended matterin the brain?
5. Descartes also appealed to the claim that the mind-body union is aprimitive notionthat cannot be further explained. Just as we understand extension through spatial intuition and thought through self-awareness, we grasp the union of mind and body throughlived experiencerather than through intellectual analysis.