Who was Plato?

Plato first encountered Socrates in his youth, initially in the company of other Athenian boys, and eventually became part of Socrates's inner circle. Socrates had redirected Greek philosophical inquiry away from questions about the natural world toward ethics and politics, challenging received ideas through a rigorous method of questioning. This approach left a permanent mark on Plato, who would go on to feature Socrates as the central speaker in nearly all of his philosophical dialogues.

As Plato came of age, he imagined a life in public affairs. Those ambitions were complicated by the political upheavals following Athens's defeat by Sparta in 404 BC, which brought to power the brutal oligarchy known as the Thirty Tyrants. Two of Plato's own relatives, Critias and Charmides, were among the Thirty. Plato was invited to join the administration but declined, repelled by the group's atrocities, including their attempt to implicate Socrates in the unlawful seizure of the democratic general Leon of Salamis. The prosecution of Socrates by Anytus, which followed the restoration of democracy, ended whatever remained of Plato's political ambitions.

After the death of Socrates, Plato remained in Athens for roughly three years before embarking on a period of intensive intellectual travel. He studied in Megara with Euclid of Megara, founder of the Megarian school of philosophy. Back in Athens around 394 BC, he studied mathematics alongside figures including Archytas of Tarentum, Theaetetus, and Leodamas of Thasos in the grove of Hecademus, northwest of the city. He also traveled to southern Italy to study with Archytas and other Pythagoreans, an encounter that left a significant impression on his thinking about the relationship between mathematics, abstract reasoning, and the nature of the soul.

Around 385 BC, Plato visited Syracuse, then ruled by the tyrant Dionysius. During this trip, Dionysius's brother-in-law, Dion of Syracuse, became one of Plato's disciples, though the tyrant himself turned against Plato. After returning to Athens, Plato founded his philosophical school, the Academy, near the sacred olive grove of Hecademus, in roughly 383 BC. The school began modestly, with a house and garden, but grew into an open area dedicated to the study of philosophy and mathematics. Aristotle of Stagira arrived there in 367 BC, shortly before Plato departed for his second visit to Syracuse.

Plato's most celebrated philosophical contribution is the Theory of Forms, first introduced in the dialogue known as the Phaedo. The theory holds that the material world perceived through the senses is not the most real world — it is merely an image or copy of an unchanging realm of Forms, which are grasped by reason alone. Where individual objects like tables or acts of justice exist in the shifting physical world, there are perfect, eternal counterparts — 'tableness,' 'justice,' 'beauty' — that constitute true reality. One of Plato's most cited illustrations of this idea was the eternal truths of geometry, such as the Pythagorean theorem, which hold regardless of any physical triangle drawn in the dirt.

Alongside the Theory of Forms, Plato developed a rich account of the soul, which he believed to be immortal and subject to reincarnation. In the Republic, he divided the soul into three parts — reason, spirit, and appetite — located in different regions of the body, and used this structure to map out an analogous three-part division in society: governing philosopher-kings corresponding to reason, warrior-guardians to spirit, and productive workers to appetite. Plato's ethics centered on the idea that knowledge of what is truly good necessarily leads to good action, and that the highest object of knowledge is the Form of the Good, which he described as existing even beyond being itself.

Plato made two further visits to Syracuse, in 366 BC and 361 BC, both connected to the hope of guiding the new ruler Dionysius II toward philosopher-kingship at the urging of Dion. Neither visit succeeded. On the third trip, Dionysius kept Plato against his will, and Plato had to appeal to his friend Archytas to secure his release. After returning to Athens for the last time around 360 BC, Plato devoted his remaining years to writing, producing or revising works including the Timaeus, Sophist, Statesman, Philebus, and the Laws, his longest work, which was still unfinished at his death and was edited by a student at the Academy, Philip of Opus.

Plato died in 348 or 347 BC and was buried in the garden of the Academy. He was succeeded as head of the school by his nephew Speusippus. His complete works are believed to have survived — an extraordinary circumstance given that the writings of nearly all his contemporaries were lost. The philosopher Alfred North Whitehead captured the scale of his influence by remarking that the entire European philosophical tradition could be characterized as a series of footnotes to Plato, a judgment that reflects how thoroughly Plato's questions about knowledge, reality, justice, and the soul have shaped every subsequent generation of thinkers.