Atomist School of Ancient Greek Philosophy Texts

The Atomist school emerged in Greece during the 5th century BCE. Its first ideas are credited to Leucippus and were worked out in detail by his pupil Democritus.

Atomism holds that everything in the cosmos consists of two fundamental realities: atoms (ἄτομοι, "uncuttables") and void (κενόν). Atoms are solid, indivisible, and eternal particles, all of the same stuff yet differing in shape, size, and arrangement. The void is empty space, and it is what allows the atoms to move.

All change, and all the variety of objects we perceive, results from the combination, collision, and separation of atoms as they move without ceasing through the void. The atoms themselves never alter in their intrinsic properties: what we take for coming-to-be, perishing, or qualitative change is only a rearrangement of the underlying atomic structure. This is a purely mechanistic account, which makes no appeal to purpose or to any governing whole in explaining natural phenomena.

Leucippus, active in the 5th century BCE, is the originator of the theory; little is known of his life, and his writings survive only in the references of later authors. Democritus (c. 460–370 BCE) was a prolific writer who systematised and extended his teacher's ideas, and he is the chief source for early atomism, though only fragments of his works remain.

The theory was framed in direct opposition to the Eleatic school, which denied the reality of change and of void. Aristotle later rejected atomism, arguing against the existence of void, and his dominance in later antiquity left atomist ideas largely marginalised. A related picture appears in Plato's <cite>Timaeus</cite>, which describes the elements as composed of geometric corpuscles; Aristotle read this as a form of atomism, though it differs from the purely mechanistic model of Leucippus and Democritus. Atomist ideas found new life in the Renaissance among critics of Aristotelianism such as Giordano Bruno, and this revival fed into the mechanical philosophy of the early modern period.