Atomism (from Greek átomos: indivisible) considers every substance (including living beings) to be made up of indivisible and extremely small material particles, the atoms. Every sensual quality of perceptible bodies has to be explained by the qualities, configurations, and changes of the atoms composing it, so that the (secondary) qualities of a compound are completely determined by and reducible to the (primary) qualities of its component atoms.

Historically, atomism can be traced back to antiquity, namely to the pre-Socratic philosophers of nature, Leucippus (born c. 480/470 B.C.E.) and Democritus (c. 460–370 B.C.E.). Due to Aristotle's convincing arguments against atomism, and because of its materialistic and atheistic worldview, it was unimportant during the Middle Ages. It was only with the seventeenth century that atomism was transformed into a scientific theory. Pierre Gassendi (1592–1655) revived...