Democritus

Democritus of Abdera (c. 460 – c. 357 BCE) was a Greek philosopher and polymath, a pupil of Leucippus and, above all, the co-founder with him of atomism. He lived between the Persian Wars and the early Hellenistic world, and he is usually grouped with the pre-Socratics, although he was a contemporary of Socrates. His importance lies in proposing a universe made only of atoms and void, an idea that has weighed on the history of science so heavily that he is often considered an ancestor of modern physics.

Many anecdotes about his life survive, but historians doubt how accurate they are. He was born in Abdera, a city on the Thracian coast of the northern Aegean, into a wealthy family. According to tradition, as a young man he learned from Chaldean magi and scholars who had been left in his father's house when Xerxes I passed through the city. When he inherited his share of the family fortune, he spent almost all of it on long journeys that, according to different sources, took him to Egypt, Persia, Babylon and perhaps as far as India, in search of knowledge. Back home he lived modestly, supported by his brother, and devoted himself wholly to study.

His output was vast. Diogenes Laertius lists more than seventy titles on ethics, physics, mathematics, music, medicine and crafts. None survives complete; what we know comes from quotations by other authors, above all Aristotle, who treated him as a serious rival in natural philosophy. Among his best-known works was the Great World Order.

His doctrine holds that only atoms exist, indivisible and alike in kind but different in shape, arrangement and position, together with the void in which they move. Everything arises from their motion and combinations. Sensory qualities such as colour or taste would not belong to the atoms themselves but would result from how they are arranged. To explain perception he offered a mechanical account: atoms streaming off objects act on our sense organs. He called chance what we take to be a hidden necessity, and he valued above all the discovery of causes. His scepticism about sense knowledge is captured in a saying attributed to him: we know nothing for certain, for truth lies in the depths.

In ethics he championed a balanced life in which tranquillity of mind is the highest good. In politics he is credited with a defence of democracy and of law with a cosmopolitan outlook. That attitude, together with his habit of smiling at human folly, earned him the name the laughing philosopher, set against Heraclitus, the weeping one.

His influence was long-lasting. Epicureanism took atomism as its physical foundation, and his ideas were revived in the early modern period, during the Enlightenment. Plato, according to an anecdote, wanted his books burned, though he never names him in his dialogues, despite criticising his cosmological theories in the Timaeus.