Doubt and certainty › The External World

The Sixth Meditation finally addresses the existence of the physical world. Descartes has established that he exists as a thinking thing and that God exists as a perfect being. Can he now prove that bodies exist? He begins by noting that he has a strong inclination to believe in the existence of bodies. He seems to perceive them through his senses, and his imagination presents them vividly. But inclinations can be misleading. What grounds does he have for trusting them? The key move is that God is not a deceiver. Descartes has a natural inclination, implanted by God, to believe that his sensory ideas are caused by external bodies. If there were no bodies at all, this inclination would be systematically false and God would be a deceiver. But God cannot be a deceiver. Therefore, bodies exist. Bodies do not therefore appear exactly as they are. The senses serve practical purposes, such as avoiding harm and seeking nourishment, rather than revealing the true nature of things. The real properties of bodies are those that can be clearly and distinctly conceived: extension, shape, motion. Sensory qualities such as color and taste do not reliably disclose what bodies are like in themselves. Descartes allows that bodies contain differences corresponding to such perceptions without assuming that those differences resemble the qualities as we experience them. The Sixth Meditation also addresses the mind-body relationship. Descartes claims to have a clear and distinct idea of himself as a thinking, unextended thing, and of body as an extended, unthinking thing. His argument depends on God being able to create separately whatever can be clearly and distinctly conceived apart. He therefore concludes that mind and body are really distinct and that the mind can exist without the body. This is stronger than simply knowing that he thinks while doubting that he has a body. Yet they are intimately connected. Sensations of hunger, pain, and pleasure affect me directly instead of merely informing me about my body's condition. I am not in my body like a pilot in a ship, merely observing and directing it. I am somehow intermingled with it. The account leaves a causal question: how can an unextended mind affect an extended body? That question becomes explicit in Descartes' later correspondence with Princess Elisabeth. It is different from the question of whether the two substances can be conceived separately.