No thinker has had a more profound influence on Western civilization than Aristotle. In the Middle Ages many questions were settled by appeal to his authority alone, and his position was so preeminent that he was often referred to simply as 'the philosopher'. His work represents a vast, encyclopedic treatment of virtually every field of knowledge: logic, rhetoric, ethics, politics, metaphysics, poetry, biology, zoology, physics, psychology. The depth and clarity of his understanding are remarkable, and nowhere more so than in the Nicomachean Ethics and the Politics . Modern science may have left the ancient Greeks far behind, but modern behavior has not. The basic questions of human conduct, both for individuals and societies, remain largely unchanged; and no one has ever illuminated these more precisely, or more constructively, than Aristotle. Aristotle (384-322bce) was born in northern Greece and studied in Athens at Plato's Academy, where he remained for many years as a teacher. He spent a short period as tutor to Alexander the Great, son of Philip II of Macedon. In 335 he returned to Athens and set up his own school, called the Lyceum.