Rene Descartes · Philosophy
Descartes argues that mind and body are two utterly different substances - thinking and unextended versus extended and unthinking - distinct enough to exist apart. This dualism shapes the modern mind-body problem.
Out of the cogito and the meditations that follow, Descartes draws one of the most consequential doctrines in the history of philosophy: dualism, the view that reality contains two fundamentally different kinds of substance. The first is mind (or soul), whose whole essence is thinking - consciousness, in all its forms: doubting, understanding, willing, imagining, sensing. A mind is unextended; it has no size, shape, or location; you cannot measure it or cut it in half. The second is body (or matter), whose whole essence is extension - being spread out in space, having size, shape, position, and motion. A body is unthinking; it is mere mechanism, governed entirely by the laws of physics, like a clock or a machine. These two essences, thought and extension, have nothing in common: thinking is not a kind of extension, and extension is not a kind of thinking. A human being, uniquely, is a union of the two - a thinking mind joined to an extended body. But the two are, in their natures, completely distinct.
Why does Descartes think mind and body are really distinct substances, and not just two aspects of one thing? His central argument turns on conceivability and clear and distinct perception. He can clearly and distinctly conceive of himself - his mind - existing without a body: recall that in the depths of doubt, he was certain of his own existence as a thinking thing while still doubting that any body, even his own, existed. He can also clearly and distinctly conceive of body as merely extended, without any thought. Now, Descartes holds that whatever I can clearly and distinctly conceive as existing apart, God can bring about as existing apart; and things that can exist apart from each other are really distinct. Since I can clearly and distinctly understand mind without body and body without mind, the two are capable of existing separately, and therefore they are really distinct substances. The mind, he concludes, is “entirely and truly distinct from my body, and may exist without it.” This argument is also the basis of his hope for the soul’s immortality: if the mind is a substance distinct from the body, the death and decay of the body need not entail the death of the mind.
One of the most influential consequences of Descartes’ dualism was his vision of the living body - animal and human alike - as a machine. Since the body’s essence is mere extension governed by mechanical laws, all its functions that do not require thought - digestion, the heartbeat, breathing, reflexes, the movement of the limbs - can in principle be explained mechanically, as the workings of an intricate hydraulic and mechanical automaton, with no need to invoke a soul. Descartes went so far as to hold that animals, lacking rational souls, are pure machines - complex automata without genuine consciousness. In humans, the rational soul is added to the bodily machine and joined to it (he thought, at the pineal gland), so that a human being is, as it were, a thinking pilot in a mechanical vessel - though Descartes insisted the union is more intimate than a pilot in a ship, since we feel our bodily states from within. This mechanical conception of the body was enormously fruitful for physiology and medicine: it licensed the study of the body as a physical system obeying physical laws, and it is an ancestor of modern mechanistic biology. But it also sharpened the puzzle of the mind: if the body is a complete machine, what exactly does the immaterial mind add, and how does it connect to the machine at all?
This is the opening of the lesson. The rest — the dialogue, the primary source, and the recall — is in the app.
You learned that Descartes held mind and body to be two distinct substances: the mind is thinking and unextended, the body extended and unthinking. Explain his argument that they are really distinct, and the problem of how they interact.
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