Substance dualism and the problem of mind-body interaction

What this dot point is asking

This dot point belongs to Unit 2 of the TASC Philosophy course, the mind/body problem, which asks about the nature of the relationship between the mind, or consciousness, and the physical world. The problem has been discussed since Plato, but the modern debate begins with Descartes, whose dualism sets the agenda that later physicalist and functionalist theories react against.

Cartesian substance dualism

Descartes argued that he could clearly conceive of his mind existing without his body, since he could doubt that he had a body but could not doubt that he was thinking. From this he concluded that mind and body are really distinct. The mind is a thinking, unextended substance whose essence is consciousness; the body is an extended, unthinking substance governed by physical laws. On this picture you are essentially your mind, and the body is a vehicle the mind inhabits and steers.

The interaction problem

The difficulty is immediate. Our minds and bodies plainly seem to affect each other: deciding to stand makes you stand, and a stubbed toe makes you feel pain. But if the mind has no physical properties and occupies no place, how can it push on the matter of the brain, and how can physical events in the brain reach into a non-spatial mind? Princess Elisabeth of Bohemia pressed exactly this objection to Descartes in their correspondence, asking how something immaterial could move a body. Descartes suggested the interaction occurred in the pineal gland, but this only relocates the puzzle, since the question of how the immaterial moves the material remains.

Dualist responses

Three classic responses try to save dualism from the interaction problem. Interactionism, Descartes' own position, simply maintains that mind and body do causally interact in both directions, accepting the interaction as a basic fact even if its mechanism is obscure. Occasionalism, associated with Nicolas Malebranche, denies any direct causal link: on the occasion of a mental event God brings about the corresponding bodily event, and conversely, so the only true cause is divine. Parallelism, developed by Gottfried Leibniz, holds that the apparent causal link is an illusion; mind and body do not interact at all but run in perfect, pre-established harmony, like two clocks set in step, so that mental and physical events correspond without one causing the other.

Evaluating dualism

Dualism captures the powerful sense that conscious experience is not just physical motion, a point modern philosophers raise through the difficulty of explaining why brain activity is accompanied by any felt experience at all. Its enduring weakness is the interaction problem. Interactionism leaves the mechanism unexplained and seems to violate the conservation of energy in physics. Occasionalism and parallelism avoid the mechanism only by invoking God or a vast pre-arranged harmony, which many find extravagant. These costs are precisely what push the Unit 2 debate toward monist theories that identify the mind with the physical brain or with functional states. For the exam, set out dualism fairly, press the interaction problem, and weigh whether any response rescues it.