Aristotle (384-322 B.C.) - Plato's greatest student, Aristotle represents the third generation, and is the third great philosopher of Classical Greece. Unlike Socrates, whose work focused strictly on philosophy, and Plato, who was a philosopher and mathematician, Aristotle was a true polymath. He studied a wide range of subjects including philosophy, physics, metaphysics (which deals with explaining how the physical world works; sort of a hybrid of philosophy and physics, for which Aristotle is considered the founder), logic, rhetoric, politics, poetry, biology, zoology and more. Like Plato, he also founded a school, the Lyceum in 335 B.C. It survived until 86 B.C., when it was destroyed after Lucius Cornelius Sulla sacked Athens. Born in Stagira, he moved to Athens when he was 18 to study under Plato and stayed for 20 years, until Plato's death. From there he moved to Assos on the northwest coast of Asia Minor and continued to study on his own. It was here that he branched out into the study of the physical world, namely marine biology, zoology and metaphysics. His observations in the physical sciences were considered the standard through the Middle Ages until they were replaced by Newtonian physics.

In 343, he was asked by Philip of Macedon to tutor his son, Alexander (the Great). Aristotle left for Pella, the capital of Macedon, and taught Alexander for two or three years, from the ages of 13 to 15. Unfortunately, we have no record of their mentor-student relationship; how well they got along or what kind of student Alexander was. Aristotle returned to Athens in 335 where he founded the Lyceum. Actually, it was formally founded at this time, but had existed as a gymnasium long before then. Aristotle added the Peripatetic school, which offered studies in philosophy and physical sciences. He left Athens in 323, the same year Alexander died, probably for fear of anti-Macedonian sentiment which had always been present since Philip conquered Greece, and died the following year.