In lecture four, we consider the life and philosophy of Aristotle of Stagira, a pupil of Plato who rose from the fringes of the Greek world to transform civilization at its center in Athens. The lecture explores Aristotle's wide-ranging contributions, including his metaphysics of substance and causation, his teleological view of nature, and his psychology of the soul. It also examines his ethics, centered on eudaimonia, and his politics, grounded in the concept of humans as "political animals." These ideas highlight the systematic and empirical character of his thought, which departed in significant ways from Plato's philosophy.