Aristotle is counted among the greatest of philosophers for his inquiries into almost every branch of knowledge, including ethics, aesthetics, physics, and biology. In particular, his empirical research into aspects of nature and history, including a lengthy classification of animals, was a truly new phenomenon in the Greek world.

The son of Nichomachus, a physician of Stageira in Thrace who served the Macedonian king Amyntas II, Aristotle went to Athens in 368 B.C. when he was about 17 years old to study at the philosopher Plato's Academy. He studied there for 20 years, but left after Plato died and went to Assos on the coast of Asia Minor to found a branch of the Academy. It was here that he married Pythias. Three years later he went to the island of Lesbos where he met Theoph rastus, who became his most celebrated disciple. In 343B.C., King Philip of Macedon...