440 BC

Atomism

Leucippus and Democritus develop early Greek atomism

The writings of one of antiquity's most prolific thinkers vanished. His atoms survive largely in quotations by the people arguing against him.

Nothing happened in 440

No surviving ancient evidence dates a proposal by Democritus to 440 BCE. The year is a conventional approximation, not a recorded moment of announcement, composition or publication.

Ancient chronologies for him conflict; even his commonly cited birth around 460 BCE is approximate.

The Greek tradition also does not give him sole credit. It normally names Leucippus — a fifth-century figure of unknown precise dates — as atomism's originator, with Democritus taking the theory over and systematising it.

Atoms and void

The early atomists posited two fundamental realities: solid, indivisible bodies called atoms, and the void through which they move and combine. Atomos means "uncut" or "indivisible."

Their atoms had no colours or tastes. Only size, shape, arrangement and position were available to explain the sensory world, and some atoms were imagined with hooks and barbs that could become entangled.

Modern scholars generally read the theory as a response to Eleatic arguments about being and change — preserving unchanging material principles while explaining visible change as rearrangement — and dispute whether the atoms were conceptually indivisible, physically unsplittable, or both.

Preserved by critics

Democritus's own works survive only in fragments and secondhand reports, with Aristotle — who argued against the atomists on void and continuity — providing much of the strongest evidence.

Because nearly all reports either combine the two thinkers or discuss Democritus alone, the individual contributions of Leucippus and Democritus often cannot be separated.

The theory was not abandoned after Aristotle: Epicurus founded an atomist school in Athens around 306 BCE, and atomism remained a live ancient tradition long before John Dalton's chemical atomic theory arose in a very different setting.

Sources

Researched 24 Aug 2026 5 sources not yet audited Date disputed

How this was checked

Researched from the web into a fact sheet and rewritten from that sheet. This article has not yet had an independent model audit. How the pipeline works →

Date disputed. Sources disagree; the research places it at ~-440.

What the sources leave uncertain

The year 440 BCE is an unsupported conventional approximation, not a verified date of announcement, composition, or publication.
Ancient chronologies for Democritus conflict; even his commonly cited birth around 460 BCE is approximate.
Because almost all reports combine the two thinkers or discuss Democritus alone, individual contributions by Leucippus and Democritus cannot always be separated.
Scholars dispute whether Democritean atoms were conceptually indivisible, physically unsplittable, or both.