# Leucippus

Leucippus (fl. c. 440 BCE) is the philosopher about whom we know least and to
whom we owe most. Epicurus is reported to have denied that he existed at all,
and some modern scholars have agreed. Aristotle and Theophrastus, who had
better sources, treated him as a real person, the teacher of Democritus, and
the first to say that the world is made of atoms moving in a void. One sentence
of his survives, and one book title, *The Great World-System*, which was later
listed among the works of his more famous pupil.

## The problem he inherited

Parmenides had argued that what is cannot come from what is not, that there is
no empty space, and that therefore nothing really moves or changes. Zeno had
defended him with paradoxes. The Ionians had gone on describing a world of
change as though nothing had been said. Leucippus took the Eleatic argument
seriously and set out to save motion without denying it.

## Atoms and void

His answer was to grant Parmenides his "what is" and add a "what is not" beside
it. Being is not one thing but infinitely many, each tiny, solid, indivisible
and unchanging: the atoms. Between them lies the void, which is nothing, yet
exists. Atoms differ only in:

- **shape**, as the letter A differs from N;
- **arrangement**, as AN differs from NA;
- **position**, as N differs from Z when turned.

Every sensible quality, colour, taste, warmth, is the effect of these three
differences on our organs. Coming-to-be is atoms joining; passing-away is
atoms parting. Nothing is created and nothing is destroyed; things are only
rearranged.

## Necessity

The one surviving sentence is this:

> Nothing happens at random; everything happens out of reason and by
> necessity.

There is no purpose in the cosmos, and no chance either. Atoms collide, tangle,
and form vortices; the vortices sort heavy from light and grow into worlds,
without number, some forming while others fall apart. Ours is one of them.

## Legacy

Democritus worked the system out in detail; Epicurus adapted it and gave the
atoms a small swerve to make room for free will; Lucretius put it into Latin
verse. When the idea returned in the seventeenth century, it returned under the
old name, and modern chemistry kept it. Leucippus, if he existed, is the
quietest founder in the history of science.

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*Stoa Press · Philosophy Essays · Markdown edition*