Aristotle (384-322 BC) is one of the principal figures in classical Greek philosophy. He was born in Stagira, on the Aegean seacoast, where his father was court physician to the Macedonian kings. Aristotle was educated in the natural sciences by his father and studied for 20 years at Plato’s academy of philosophy in Athens. After Plato’s death in 342 BC, Aristotle was called to Macedonia, where he became tutor to the young Alexander the Great. When Alexander succeeded to the Macedonian throne in 336, Aristotle went to Athens and established the Lyceum, his school of philosophy. His customary method was to give lectures while he and his students walked amid nature, hence the label “peripatetic school of philosophy.” After Alexander’s death, political turmoil forced Aristotle to flee to the province of Euboea, where he died.

Aristotle’s writings—only a fraction of which have survived—covered all branches of knowledge current in his time, from ethics and rhetoric to natural science. Although influenced by Plato’s philosophy, Aristotle went his own way on some philosophical issues. In contrast to Plato’s idealism, which held that ideas alone have true being and reality, Aristotle believed in discovering truth by closely observing the natural world.