The pre-Socratic philosophers Leucippus and Democritus are credited with the first theories of atoms. They basically said that all matter is composed of atoms, or constituent parts that cannot be further divided into smaller parts. Leucippus and Democritus, remember, were Greek, and the word atom derives from the prefix a- (meaning “not”) and the word tomos (meaning “cut”), hence “not cut”. These atoms could, then, not be cut into smaller pieces, so to speak. Rather, they were the fundamental pieces that, by their inherent shape and in the ways that they were arranged into material things, gave those materials their physical properties.
Aristotle, however, raised objections to the earlier atomists, pointing out what he saw as problems arising from their theory as pertains to indivisible atoms being minima and their effects on time and motion. Epicurus attempted to reconcile atomism with Aristotle’s objections. Some of the Gottfried Wilhelm von Leibniz’s objections to atomic theory in the late 17th century seem to me to resemble Aristotle’s earlier objections.
Atomic theory was arguably vindicated in the 19th century by the chemist John Dalton, although his atoms were not quite the same atoms that the ancient Greeks had in mind. Rather, the new atomic theory was one of atoms composed of protons, neutrons, and electrons — hardly indivisible; furthermore, even the protons and neutrons themselves can be “cut” into quarks. What’s more, there are different types of quarks, which along with leptons, are fermions, and electrons are a type of lepton.
So, it would seem, the pre-Socratics were onto something, but the idea of what exactly an atom is has changed much since the time of Leucippus and Democritus.
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