In order to understand Plato's theory so far as possible without prejudice or distortion, the author has been at pains to distinguish it from other theories which also make love the key to everything; throughout the book, therefore, he sustains a sort of dialogue among these rival theories, the Platonic, the Christian, the Freudian and a rather vague tradition which he calls the 'Romantic'. The study yields some surprising discoveries, about the changes which took place in Plato's thinking late in his life and about the exact nature of Aristotle's quarrel with Platonic philosophy -- as well as new light on such famous passages as the Sun, the Line, and the Cave in the "Republic".