A typical textbook account of the philosophy of mind in the seventeenth century goes something like this. Descartes believed in two kinds of stuff, mental stuff and material stuff, substances distinct in nature that go together to constitute a single human being. But Descartes also took it for granted that these two substances were capable of genuine causal interaction, that minds can cause bodily events, and that bodies can cause mental events, i.e., that acts of will can genuinely cause changes in the state of the human body, and that the state of the sensory organs and the brain can cause sensation and imagination in the mind.