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 finds conceptions of the mind that are coherent and deeply integrated with both philosophers' views about such topics as the relation between body and soul, or the nature of the virtues.