Leucippus

Ancient Greek · Europe · 480 to 420 BCE

Greek thinker who is named as the first to teach that everything is made of atoms moving in empty space.

What it is

Leucippus was a Greek philosopher who was active in the fifth century BCE. Aristotle and Theophrastus credit him with starting atomism, the view that everything is made of tiny indivisible particles moving in empty space.

Almost nothing is certain about his life. We do not know where he lived: Miletus, Abdera and Elea have all been named. The little we know comes from later writers. He had a famous pupil, Democritus, and the two men are so closely tied that their ideas are hard to tell apart.

The main ideas

Atoms. All things are made of very small particles that cannot be divided. They are always in motion, and when they collide and regroup they form the things we see.
Empty space. The atoms move in a void. Without empty places, he reasoned, there would be nowhere for anything to move into.
An answer to Parmenides. The Eleatic school argued that the void cannot exist, so motion is impossible and all things are one. Leucippus kept both change and the many things of ordinary life by saying that unchanging atoms persist and only rearrange themselves in the void.
A world from a whirl. Atoms gathered together in a whirl, and from that whirl the cosmos formed.

What it looks like in practice

Picture someone watching a pile of sand grains shift in the wind, and asking whether a dune is anything more than the grains and the space between them. Leucippus would say that all change is only grains of this kind being rearranged. This is an illustration of the idea, not a passage from his writing.

Books and moments

The Great World System. One of two works linked to him, though it has sometimes been given to Democritus.
On Mind. The other work attributed to him. Only fragments of his writing remain.
A shared school. He developed atomism together with his pupil Democritus, who is understood to have built on it.

Questions and criticism

Whose ideas? Because Democritus built on his work and the two are so often named together, it is difficult to say which ideas belong to Leucippus.
Where did he live? Different cities have been proposed, and it is fair to ask how much weight any of them deserves.
Does it match modern atoms? Ancient atomism is often compared with modern theories of matter, but scholars warn against assuming that the ancient atomists shared modern ideas about atoms and their motion.

Close neighbours

The page on Democritus covers his pupil and the fuller atomist system. The pages on Parmenides and Zeno of Elea cover the Eleatic school he answered.

Written by epchē in our own words, and checked against independent sources on 29 October 2026. The sources are listed below.

Who they connect to

Influenced

Democritus · Ancient writers name him as the founder of atomism and the teacher of Democritus.

Other Ancient Greek thinkers

Thales of Miletus · 624 to 546 BCE
Anaximander · 610 to 546 BCE
Anaximenes · 586 to 526 BCE
Pythagoras · 570 to 495 BCE
Xenophanes · 570 to 475 BCE
Heraclitus · 535 to 475 BCE
Parmenides · 515 to 450 BCE
Anaxagoras · 500 to 428 BCE
Empedocles · 494 to 434 BCE
Zeno of Elea · 490 to 430 BCE

Sources we used

Leucippus · Encyclopaedia Britannica, read on 29 October 2026
Leucippus · Wikipedia, read on 29 October 2026
Democritus · Stanford Encyclopedia of Philosophy, read on 29 October 2026