Plato

(c. 428 bc–347 bc) Greek philosopher

Little is known of Plato's early life. He apparently came from an established Athenian family active in politics. With the execution of Socrates in 399 bc he left Athens for some years and visited, among other places, Sicily in about 389 where he made contact with the Pythagoreans and much impressed Dion, the brother-in-law of Dionysius I, the tyrant of Syracuse. On his return to Athens shortly afterward he founded in about 387 the most famous of all institutions of learning, the Academy, which in one form or another remained viable until its closure by the emperor Justinian in ad 529. On the death of Dionysius I in 367 Plato returned to Sicily at the invitation of Dion to try to educate Dionysius II as the new philosopher-king, attempting once more in 361. The visits were disastrous and ended with Plato dismissing Sicily as a place where “happiness was held to consist in filling oneself full twice a day and never sleeping alone at night.”

It is virtually impossible to overestimate the impact of Plato on Western thought. His views, preserved and transmitted through the distorting medium of neo-Platonists and Christian fathers alike, came to influence theology, politics, ethics, education, and aesthetics just as much as they have (and still do) metaphysics and logic. Nor were his contributions to the development of science negligible. It was Plato who posed to the astronomers of his day, such as Eudoxus, the question: “By the assumption of what uniform and orderly motions can the apparent motions of the planets be accounted for?” The request that there should be but one explanation applying to the seemingly disparate observed motions of each planet did much to shape the development of Greek astronomy and to add to it a characteristic dimension of model building lacking, for example, in Babylonian astronomy.

He also, in the Timaeus, under the influence of the Pythagoreans of Sicily, introduced an alternative form of atomism to that of Democritus. He began with the result of Theaetetus that there can be only five regular solids, the tetrahedron, cube, octahedron, dodecahedron, and icosahedron, and went on to assign to each of the four elements of Empedocles a characteristic shape of one of the regular solids. The cube as the most stable is assigned to the least mobile element, earth; the pyramid is assigned to fire; the octahedron to air; and the icosahedron to water. To the remaining figure, the dodecahedron, most closely approaching the sphere, Plato associated the ‘spherical heaven’.

The main significance of Plato's thought for science was thus to establish the vital tradition, originating with the Pythagoreans and finding ready echoes in the work of Galileo and Kepler, of the mathematical analysis of nature. It is said that an inscription over the vestibule of the Academy read: “Let no one enter here who is ignorant of Geometry.”