384 B.C. - 322 B.C. Greek philosopher best known as the author of Ethics. Aristotle placed great emphasis in his school on direct observation of nature, and in science he taught that theory must follow fact.

470 B.C. - 399 B.C. Greek philosopher whose indefatigable search for ethical knowledge challenged conventional mores and led to his trial and execution on charges of impiety and corrupting the youth.

428 B.C. - 347 B.C. Plato, originally named Aristocles (Plato means "broad-shouldered"), was one of the early stars of Western philosophy.