Plato was born, probably in Athens, into a distinguished and wealthy, aristocratic family, the son of Ariston and Perictone. Little is known of his early life. Any youthful political ambitions must have withered as he witnessed the decline of imperial Athens after the death of the statesman Pericles in 428 B.C.; the excesses of the conservative faction, with which he had family connecitons; the ensuing civil strife, and the equally punitive reaction of the restored democracy, which condemned to death his great friend and mentor, Socrates, in 399 B.C. Plato immortalized the story of Socrates' trial and last days in three of his dialogues: the Apology, the Crito, and the Phaedo, where his profound affection and respect for Socrates come through vividly.
After the "execution" of Socrates, he and other followers took temporary refuge at Megara with the philosopher Euclidies, and he then travelled widely in Greece, Egypt, the Greek cities in Italy (where he no doubt encountered Pythagoreans), and Sicily (where he made friends with Dion, brother-in-law of Dionysus I, the ruler of Syracuse). He returned to Athens in C.387 B.C. and founded the Academy, which became a famous center for philosophical, mathematical, and scientific research, and over which he presided for the rest of his life. He visited Sicily again in 367 B.C., at Dion's request, with the intention of training Dionysus II to become a philosopher-statesman, but despite a second visit during 361-360 B.C., which placed his life in danger, the attempt failed completely.
Plato's writings consist of some 30 philosophical dialogues and a series of Letters, of which the Seventh is the most important (biographically and philosophically), and only the Seventh and Eighth are likely to be genuine. The dialogues are conventionally divided into three groups: early, middle, and late - through the exact relative chronology of individual dialogues is a vexed and probably insoluble problem of scholarship.
The early "Socratic dialogues" have Socrates as the principal character, usually portrayed interrogating his unfortunate interlocutors about the definition of different moral virtues (eg piety in Euthrphro, and courage in the Laches). Their initially confident assertions are shown to be confused and contradictory, and all parties end up sharing Socrates' professed perplexity.
The middle dialogues show the character "Socrates" expressing more positive, systematic views, which are usually taken to be Plato's own. This group includes the most dramatic and literary of the dialogues, the Symposium, the Gorgias, Phaedo, and Republic, and presents such famous Platonic doctrines as the theory of knowledge as recollection; the immortality of the soul; the tripartite division of the soul, and above all the theory of forms (or ideas). This contrasts the transient, material world of particulars (objects merely of perception, opinion, and belief) with the timeless unchanging world of forms (the true objects of knowledge). The Republic also describes Plato's celebrated political utopia, ruled by philosopher-kings who have mastered the discipline of dialectic and studied the hierarchy of the forms, including its apex: the form of the Good. The details of this visionary state: the rigid class structure of workers, soldiers, and rulers; the education of the rulers (both men and women); common ownership of property; allegiance to the state overruling that to family; the totalitarian powers of the state - all these have been variously idealized, attacked, misinterpreted, and imitated in subsequent political theory and literature.
The third group of "late" dialogues is generally less literary in form, and represents a series of sustained and highly sophisticated criticisms of the metaphysical and logical assumptions of Plato's doctrines of the middle period. The Permenides, Theaetetus, and Sophist in particular have attracted the interest of contemporary analytical philosophers, and contain some of Plato's most demanding and original work. Taken as a whole, his philosophy has had a pervasive and incalculable influence on almost every period and tradition, rivalled only by that of his greatest pupil, Aristotle.