Aristotle completes the great philosophical triumvirate of ancient Greece. Born in 384 B.C. to the court physician of the king of Macedonia, he began to study the natural sciences at an early age. After his father died in about 367 B.C., the young philosopher went to Athens to further his education. In Athens, Aristotle became a member of Plato's Academy and maintained a constant dialogue on many subjects with Plato until Plato’s death around twenty years later.

After Plato's death, Aristotle left Athens, founded new academies in Assus and Mytilene, and for three years (345-342 B.C.) tutored the young Alexander the Great at Pella, the capital of Macedonia. In 335 B.C. he returned to Athens and established the Lyceum, a rival school to the Academy of Plato. Indicative of Aristotle's competing philosophical position, the Lyceum was a center for philosophic contemplation and empirical research. Aristotle's surviving works appear to have been lectures given at the school. They cover a variety of topics, including politics, physics, ethics, economics, a historical analysis of the Athenian Constitution, and much more. In epistemology, Aristotle is best known for his argument in favor of the validity of sense perception and scientific observation against the Platonic view of ideal forms dimly perceived through corrupted matter. After Alexander died, an anti-Macedonian backlash in Athens forced Aristotle to flee northward to Chalcis, where he died a year later, in 322 B.C.

Aristotle's philosophy was as influential on Western thought as Plato's. The medieval Scholastic movement was in its essence an attempt to reconcile both philosophies with Christian doctrine. From this effort came the modern discipline of theology.