Hendrik Lorenz presents a comprehensive study of Plato's and Aristotle's conceptions of non-rational desire. They see this as something that humans share with animals, and which aims primarily at the pleasures of food, drink, and sex. Lorenz explores the cognitive resources that both philosophers make available for the explanation of such desires, and what they take rationality to add to the motivational structure of human beings. In doing so, he exposes a remarkabledegree of continuity between Plato's and Aristotle's thought in this area. He also sheds fresh light, not only on both philosophers' theories of motivation, but also on how they conceive of the mind, both in itself and in relation to the body.