Plato (c. 427–347 BC)

Greek philosopher. He was a pupil of Socrates, teacher of Aristotle, and founder of the Academy school of philosophy. He was the author of philosophical dialogues on such topics as metaphysics, ethics, and politics. Central to his teachings is the notion of Forms, which are located outside the everyday world – timeless, motionless, and absolutely real.

Plato's philosophy has influenced Christianity and European culture, directly and, through Augustine, the Florentine Platonists during the Renaissance, as well as countless others.

Of his work, some 30 dialogues survive, intended for performance either to his pupils or to the public. The principal figure in these ethical and philosophical debates is Socrates and the early ones employ the Socratic method, in which he asks questions and traps the students into contradicting themselves; for example, Iron, on poetry. Other dialogues include the Symposium, on love, Phaedo, on immortality, and Apology and Crito, on Socrates' trial and death. It is impossible to say whether Plato's Socrates is a faithful representative of the real man or an articulation of Plato's own thought.

Plato's philosophy rejects scientific rationalism (establishing facts through experiment) in favour of arguments, because mind, not matter, is fundamental, and material objects are merely imperfect copies of abstract and eternal ‘ideas’. His political philosophy is expounded in two treatises, The Republic and The Laws, both of which describe ideal states. Platonic love is inspired by a person's best qualities and seeks their development.

Born of a noble family, Plato entered politics on the aristocratic side, and in philosophy became a follower of Socrates. He travelled widely after Socrates' death, and founded an educational establishment, the Academy, in order to train a new ruling class.

In science, geometry – with its premise of symmetry and the irrefutable logic of its axioms – had the most appeal to Plato. The universe had to be spherical because the sphere was the perfect volume; for the same reason the movements of the heavenly bodies had to be circular and uniform. Moreover, the Earth, which lay at the exact centre of the cosmos, was a sphere and was surrounded by a band of crystalline spheres which held in place the Sun, the Moon, and the planets.