atomism, philosophic concept of the nature of the universe, holding that the universe is composed of invisible, indestructible material particles. The theory was first advanced in the 5th cent. B.C. by Leucippus and was elaborated by Democritus. Epicurus restated the doctrine, giving the atoms weight. Atomism, nearly forgotten in later antiquity and the Middle Ages, was revived in the 17th cent. by Pierre Gassendi and was given consideration by Robert Boyle, Isaac Newton, and John Locke.
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