In 407 B.C. he became a pupil and friend of Socrates. After living for a time at the Syracuse court, Plato founded near Athens the most influential school of the ancient world, the Academy, where he taught until his death. His most famous pupil there was Aristotle. Plato's extant work is in the form of epistles and dialogues, divided according to the probable order of composition. The early, or Socratic, dialogues, e.g., the Apology, Meno, and Gorgias, present Socrates in conversations that illustrate his major ideas-the unity of virtue and knowledge and of virtue and happiness. They also contain Plato's moving account of the last days and death of Socrates. Plato's goal in dialogues of the middle years, e.g., the Republic, Phaedo, Symposium, and Timaeus, was to show the rational relationship between the soul, the state, and the cosmos. The later dialogues, e.g., the Laws and Parmenides, contain treatises on law, mathematics, technical philosophic problems, and natural science. Plato regarded the rational soul as immortal, and he believed in a world soul and a Demiurge, the creator of the physical world. He argued for the independent reality of Ideas, or Forms, as the immutable archetypes of all temporal phenomena and as the only guarantee of ethical standards and of objective scientific knowledge. Virtue consists in the harmony of the human soul with the universe of Ideas, which assure order, intelligence, and pattern to a world in constant flux. Supreme among them is the Idea of the Good, analogous to the sun in the physical world. Only the philosopher, who understands the harmony of all parts of the universe with the Idea of the Good, is capable of ruling the just state. In Plato's various dialogues he touched upon virtually every problem that has occupied subsequent philosophers; his teachings have been among the most influential in the history of Western civilization, and his works are counted among the world's finest literature.