The Atomists: atoms and void

Leucippus and his pupil Democritus of Abdera push the Pluralist project to its most rigorous extreme. Their eternal beings are atoms (atomon = uncuttable, indivisible). Atoms are infinitely many, ungenerated, imperishable, and internally unchanging — full little pieces of pure being, each answering Parmenides’ description of what-is.

Atoms are all made of the same solid stuff; they differ only in shape (rhusmos), arrangement (diathigē), and position/turning (tropē). A rough atom, a round one, an A next to an N versus an N next to an A — from these bare geometric differences the Atomists build the entire sensible world. No qualities inside the atom, only geometry.

But atoms need room to move and combine. So the Atomists make their boldest claim: alongside the full (to plēres = atoms) there is the empty — the void (to kenon). And they say, flatly, that “what-is-not” is no less than “what-is.” Empty space is real. This is a direct, deliberate contradiction of Parmenides.

With atoms and void in place, all change is reduced to atoms combining and separating as they move through the void. Coming-to-be is atoms interlocking; perishing is their scattering. As with the other Pluralists, nothing is truly created or destroyed — but here the ontology is starkest: reality is just full and empty, body and space.

And atoms move by necessity (anankē), not purpose. Atoms collide, rebound, and get entangled by their shapes; a cosmic vortex sorts like toward like. There is no goal, no design, no chooser — only the blind mechanics of impact. This is thoroughgoing mechanistic materialism and determinism: every event is fixed by prior collisions.

This raises a sharp problem: if the world is only atoms and void, what about color, taste, sound, warmth? Democritus draws a famous line between what really belongs to things and what exists only in our experience of them.

His verdict, in fragment B9/B125: “By convention (nomōi) sweet, by convention bitter, by convention hot, by convention cold, by convention color; but in reality (eteēi) atoms and void.” Sweetness is not in the world; it is what a certain arrangement of atoms does to us. The atoms and their motions are objectively real; the sensory qualities are, we would say, secondary qualities.