Democritus

Democritus of Abdera (c. 460 – 370 BCE) was, with his teacher Leucippus, the
principal architect of ancient atomism, one of the most prescient theories
the Greek world produced. A wealthy and widely travelled native of Thrace, he
was reputed to have written voluminously on ethics, physics, mathematics,
music, and natural history, though almost all of his work is lost and survives
only in reports and quotations by later authors.

The core of the atomist doctrine is disarmingly simple: nothing exists but
atoms and the void. Atoms are indivisible, indestructible particles, infinite
in number and varied in shape and size, moving eternally through empty space.
The void is the nothingness in which they move — a bold postulate, since the
Eleatics had argued that "what is not" cannot be. All the qualities of the
visible world arise from the arrangement, position, and motion of atoms as
they collide, cling together, and disperse. There is no purpose in this
process, only mechanical necessity.

From this followed a striking distinction between the world as it is and the
world as it appears. "By convention sweet, by convention bitter, by
convention hot, by convention cold, by convention colour," Democritus wrote;
"but in reality atoms and void." The sensible qualities we perceive are
products of the interaction between atoms streaming off objects and the atoms
of our sense organs, not features of things in themselves. In this he
anticipated, by more than two millennia, distinctions that would reappear at
the dawn of modern science.

Democritus did not confine himself to physics. A substantial body of ethical
sayings is attributed to him, centred on the ideal of cheerfulness or
good spirits (euthymia), a tranquil and balanced state of mind attained
through moderation and the avoidance of excess. This reputation for serenity
earned him the affectionate epithet "the laughing philosopher," set against
the weeping Heraclitus in later tradition.

His atomism found no favour with Plato, who is said to have wished his books
burned, but it was taken up and developed by Epicurus and transmitted to the
Roman world through Lucretius. When atomic theory re-emerged in the
scientific revolution, thinkers looked back to Democritus as its remote and
remarkable forerunner.