Plato

Plato (c. 428–348/347 BCE) was born into an aristocratic Athenian family; his mother Perictione traced descent from Solon, and his stepfather Pyrilampes had served Pericles. He received the education typical of elite Athenian youth and would have entered political life had he not encountered Socrates. The execution of Socrates in 399 BCE on charges of impiety and corrupting the youth marked Plato decisively: it convinced him that no existing political order was just, and that political philosophy must be grounded in philosophical inquiry into the soul, the good, and what truly is.

Around 387 BCE, after travels to Megara, southern Italy (where he met the Pythagoreans, especially Archytas of Tarentum), and reportedly Cyrene and Egypt, Plato founded the Academy in a grove northwest of Athens. It was the first sustained institution of higher learning in the Greek world and would operate for almost nine centuries. He made three voyages to Syracuse, twice attempting to tutor the tyrant Dionysius II in the philosopher-king ideal; both ventures failed politically but are reflected in the Seventh Letter and in the Republic and Laws. He died in Athens around 348/347 BCE and was succeeded as head of the Academy by his nephew Speusippus.

His thought is preserved in roughly two dozen authentic dialogues, almost always featuring Socrates as the principal speaker. At its heart is the Theory of Forms: the claim that intelligible, eternal, unchanging entities — Justice itself, Beauty itself, the Good — are more truly real than the sensible particulars that participate in them, and that knowledge proper is knowledge of these Forms. His tripartite soul (reason, spirit, appetite) parallels the three classes of his ideal city, and the Form of the Good is the ultimate source of being and intelligibility. Late dialogues (Sophist, Timaeus, Laws) refine and self-criticize this metaphysics.

Few philosophers have so durably shaped what came after. Aristotle was his pupil. Plotinus and Neoplatonism reread him as the philosopher of a mystical ascent that would shape Augustine and the Christian Platonic tradition. Islamic philosophers (al-Farabi, Avicenna) adapted his political philosophy to monotheism. Marsilio Ficino's Florentine translations made him central to the Renaissance. Alfred North Whitehead's remark that the European philosophical tradition consists of "a series of footnotes to Plato" is hyperbole, but barely.