Plato

Key ideas

Plato's best-known idea is the theory of forms. The things we see, beautiful faces or just actions, are imperfect and changing. What makes them beautiful or just is their share in a perfect, unchanging Form of Beauty or Justice, which can be grasped only by reason. His allegory of the cave dramatises the gap between the shadows of ordinary experience and the reality behind them.

In the Republic he builds a theory of justice in the soul and in the city together. The soul has three parts, reason, spirit and appetite, and is just when reason rules. He sets this against the challenge of the ring of Gyges, which asks why anyone would be just if they could get away with injustice.

Plato also wrote the first sustained Western arguments for the immortality of the soul, a theory of knowledge as recollection, and, in the Theaetetus, the analysis of knowledge as true belief with an account, the ancestor of the definition challenged by the Gettier problem.

“Wonder is the feeling of a philosopher, and philosophy begins in wonder.”

Plato, Theaetetus 155d, trans. Benjamin Jowett

Life, briefly

Plato was born into a prominent Athenian family and became a follower of Socrates. The execution of Socrates in 399 BCE turned him away from politics. He travelled, including to Sicily, where his attempts to educate the rulers of Syracuse went badly.

Around 387 BCE he founded the Academy in Athens, which counted Aristotle among its students and lasted in some form for centuries. Unusually for an ancient author, all of his known works seem to have survived.

Major works

• Apology
• Phaedo
• Meno
• Symposium
• Republic
• Theaetetus
• Timaeus
• Laws

Schools of thought

Platonism

Further reading

• EncyclopediaStanford Encyclopedia of Philosophy: Plato
• WikipediaPlato