The Complete Works of Plato

Plato (c. 428–348 BCE) was born in Athens into one of the city's most politically connected families. His father Ariston claimed descent from Codrus, the legendary last king of Athens; his mother Perictione traced her lineage to Solon, the great lawgiver. Diogenes Laertius (3.4) reports that Plato's given name was Aristocles and that "Plato" was a nickname — from platys, "broad" — given by his wrestling coach, though the story is almost certainly apocryphal. His brothers Adeimantus and Glaucon appear as Socrates' interlocutors in the Republic; his half-brother Antiphon narrates the Parmenides. Through his mother's side, Plato was related to two members of the Thirty Tyrants — her cousin Critias and her brother Charmides — both of whom appear as title characters in his dialogues. He grew up during the Peloponnesian War and witnessed both the oligarchic terror of 404 BCE and the democratic trial and execution of Socrates in 399 BCE. The Seventh Letter (if authentic) describes how these experiences turned him from the political career typical of his class toward philosophy.

Plato associated with Socrates for roughly the last decade of the latter's life (c. 408–399 BCE). According to the Phaedo (59b), Plato was absent from Socrates' final day through illness — Diogenes Laertius repeats this but later biographers have doubted it. After Socrates' execution, Plato left Athens for Megara, where he joined the circle of the philosopher Euclides (himself present at the execution). He later traveled to Cyrene, where he studied with the mathematician Theodorus; to southern Italy, where he encountered Pythagorean philosophy and the statesman-mathematician Archytas of Tarentum; and to Sicily. At Syracuse he befriended Dion, the young brother-in-law of the ruling tyrant Dionysius I. According to later tradition (Diogenes Laertius 3.19–20), Dionysius grew hostile to the philosopher, and Plato was either sold into slavery at the market on Aegina or placed in grave danger — he was ransomed or rescued by Anniceris of Cyrene. The details vary across ancient sources, but the broad outline is widely accepted.

Around 387 BCE, Plato returned to Athens and founded the Academy in a grove sacred to the hero Academus — often described as the first institution of higher learning in the Western world. Mathematics occupied a central place: the mathematician Theaetetus and the astronomer Eudoxus of Cnidus were both associated with the school. Key members included Plato's nephew Speusippus (who succeeded him as head), Xenocrates of Chalcedon (who succeeded Speusippus), and Philip of Opus (who may have edited the Laws and composed the Epinomis). Plato's most famous student, Aristotle, joined at seventeen and remained for twenty years — first as student, then as teacher and researcher. The Academy proved remarkably durable: it continued in various forms for over nine centuries, until the emperor Justinian ordered the closure of the Athenian philosophical schools in 529 CE.

The Academy did not insulate Plato from politics. In 367 BCE, when Dionysius I died and the young Dionysius II succeeded him, Dion invited Plato to Syracuse — offering a chance to shape a philosopher-ruler in the mold of the Republic. The experiment failed: Dionysius exiled Dion and effectively detained Plato, who was eventually allowed to leave. In 361 BCE, against the advice of friends (as the Seventh Letter reports), Plato returned a third time. Dionysius again turned hostile, placing Plato under something close to house arrest. Archytas of Tarentum negotiated his release by sending a ship. The aftermath was grim: Dion seized power in Syracuse by force in 357 BCE but was assassinated in 354 BCE by his own associate Callippus — a former member of the Academy.

Plato died in Athens around 348 BCE, reportedly at a wedding feast (Diogenes Laertius, Lives 3), in his eightieth year. Unlike Aristotle's treatises, which were lost for centuries, Plato's dialogues circulated widely from the start and survived antiquity intact. The corpus was organized into nine tetralogies (groups of four) by Thrasyllus of Mendes (d. 36 CE), court intellectual to the emperor Tiberius — an arrangement that became canonical in the manuscript tradition. The surviving corpus comprises 36 works — 35 dialogues and a collection of 13 letters — spanning epistemology, metaphysics, ethics, political theory, aesthetics, philosophy of language, cosmology, mathematics, and theology. Several of the minor dialogues and most of the letters are widely regarded as spurious; the genuine works number around 26–28 depending on the scholar. The Stephanus numbers used in modern citations (e.g., Republic 509d) derive from Henri Estienne's 1578 Geneva edition and remain the standard reference system. As Alfred North Whitehead put it: "The safest general characterization of the European philosophical tradition is that it consists of a series of footnotes to Plato."