Plato c.428-c.348BC
Greek philosopher

Plato was born probably in Athens, of a distinguished aristocratic family that claimed descent from the early king Codrus, but little is known of his early life. His works show the profound influence of Socrates, who converted Plato to philosophy after early attempts at poetry. Plato gives an account of Socrates' last days in 399BC in three of his dialogues: the Apology (not strictly a dialogue, but an account of the trial), the Crito (a discussion set in Socrates' prison cell) and the Phaedo (describing Socrates' final hours and death). After Socrates' death, he and other disciples took temporary refuge at Megara with the philosopher Eucleides, and he then travelled widely in Greece, Egypt, southern Italy, where he encountered the Pythagoreans, and Sicily, where he became the friend and teacher of Dion, brother-in-law of Dionysius I of Syracuse.

Plato returned to Athens (c.387) where he founded the Academy, which was named after the grove of the hero Academus where the school was situated. It became a famous centre for philosophical, mathematical and scientific research, and Plato himself presided over it for the rest of his life. Plato refers in his Epistles to an interest in entering politics; he says that he attempted this on two occasions, in 404 after the defeat of Athens in the Peloponnesian War, and again after the restoration of democracy in 403. He was soon disillusioned with politicians, and formed the conclusion, expounded in the Republic and other writings, that the only hope for the Greek cities was to trust in philosopher-kings, who have a knowledge of goodness and are able to lead others to goodness.

He visited Sicily again on the death of Dionysius I in 367, at Dion's request, to teach Dion's nephew Dionysius II to become a philosopher-king, but Dionysius mistrusted Dion and had him banished. Plato returned to Athens and, despite a second visit in 361-60, this attempt to put principles into practice was a failure, as Plato himself went to great lengths to explain in his Epistles.

Among Plato's pupils were Aristotle, who eventually founded the Peripatetic School at the Lyceum in Athens, Speusippus, Plato's successor as head of the Academy, and Theophrastus.

Bibliography: The corpus of writings attributed to Plato consists of about 30 philosophical dialogues and 13 Epistles (Letters), of which the Seventh and Eighth are probably genuine. The Seventh is the most important biographically and philosophically.

The dialogues are conventionally divided into three groups (early, middle and late), although the exact chronology is in some cases uncertain.

The early Socratic dialogues are centred on Socrates, who is usually portrayed as interrogator in a series of questions and answers aimed at examining the validity of assumed ideas about important matters, especially about moral virtues (piety in the Euthyphro, courage in the Laches, and temperance in Charmides), and seeking conclusions about them, even though this may mean that we cannot know the truth.

In the later dialogues, Socrates expresses more positive and systematic views; it is an important question to what extent they are Socrates' views and to what extent Plato's. This group includes the most dramatic and literary of the dialogues - the Symposium, Gorgias, Phaedo and Republic - and presents the central Platonic doctrines: the theory of knowledge as recollection, the dualism of the immortal soul and the mortal body, and above all the Theory of Forms (or Ideas) which contrasts the transient, material things of this world with the Ideas that they reflect, which are the true objects of knowledge.

The Republic, which opens with the question 'What is justice?', begins like a dialogue but ends up as an exposition by Socrates. It describes a political utopia, ruled by philosopher-kings who have mastered the discipline of dialectic and, unlike the majority, have knowledge of Justice and the Good. The state is formed on a rigid class structure of workers, soldiers and rulers, on the education of the rulers (both men and women), and on communism of property and family. These last precepts have been the subject of much subsequent discussion (and sometimes misrepresentation), and have had a profound effect on later European political thought.

The final group of dialogues is generally less literary in form and represents a critical reappraisal of the metaphysical and logical assumptions of Plato's earlier doctrines. The Parmenides, Theaetetus and Sophist in particular have attracted the interest of contemporary analytical philosophers and contain some of Plato's most original and demanding work. The Laws, which represent a revision of Plato's political thinking in the light of experience (eg in Sicily), were published after his death. See also C Rowe, Plato (1986), R M Hare, Plato (1982) and J Annas, An Introduction to Plato's Republic (1981).