Democritus and the Atomists

Leucippus and his student Democritus of Abdera (c. 460–c. 370 BCE) offered the most radical answer to Parmenides. They agreed that real being cannot be divided endlessly, but they claimed there are countless tiny, indivisible particles, called atoms (from atomos, 'uncuttable'), moving through empty space, the void. Atoms differ only in shape, size and arrangement; everything we see, from water to human bodies, results from their combinations.

Qualities like color and taste, Democritus said, exist 'by convention', while in reality there are only atoms and void. The theory explained change without gods or purposes, which made it appealing to later materialists but troubling to Plato and Aristotle, who rejected it. Ancient atomism was not based on experiments, so it differs from modern atomic theory, but it was revived by Epicurus, preserved by the Roman poet Lucretius and rediscovered by early modern scientists.