Aristotle (384-322 B.C.), probably the greatest teacher who ever lived, surveyed in his Ethics the ends to which conduct should be directed. The importance of this work to a modern reader lies in Aristotle's boldness in introducing psychology into his study of human behaviour. He extended the frontiers of philosophy to include universal science, by converting ethics from a theoretical to a preactical science, based ona careful observation of life and a genuine understanding of human nature. The Ethics, the substance of lectures delivered to Aristotle's students, is lucidly translated for the Penguin Classics by J.A.K. Thomson.