Aristotle was a philosopher and scientist whose genius organized the fields of human knowledge for nearly two millennia. A student of Plato and tutor to Alexander the Great, he founded the Lyceum in Athens. Aristotle’s genius was encyclopedic; he wrote on physics, biology, zoology, metaphysics, logic, ethics, aesthetics, poetry, theater, music, rhetoric, psychology, linguistics, economics, politics, and government. He was the first to develop a formal system of logic, known as syllogism. In biology, he was a keen observer, classifying hundreds of animal species based on their characteristics. His works remained the authoritative source of scientific and philosophical thought throughout the Middle Ages.