For the Pre-Socratic philosophers the soul was the source of movement and sensation, while for Plato it was the seat of being, metaphysically distinct from the body that it was forced temporarily to inhabit. Plato's student Aristotle was determined to test the truth of both these beliefs against the emerging sciences of logic and biology. His examination of the huge variety of living organisms - the enormous range of their behaviour, their powers and their perceptual sophistication - convinced him of the inadequacy both of a materialist reduction and of a Platonic sublimation of the soul. In De Anima, he sought to set out his theory of the soul as the ultimate reality of embodied form and produced both a masterpiece of philosophical insight and a psychology of perennially fascinating subtlety. For more than seventy years, Penguin has been the leading publisher of classic literature in the English-speaking world. With more than 1,700 titles, Penguin Classics represents a global bookshelf of the best works throughout history and across genres and disciplines. Readers trust the series to provide authoritative texts enhanced by introductions and notes by distinguished scholars and contemporary authors, as well as up-to-date translations by award-winning translators.