Epicureans, Earlier Atomists, and Cyrenaics

The theory developed by Leucippus (5th cent. BCE), Democritus (470/460-380 BCE), and later Epicurus (341-271/270 BCE) and his school is commonly defined as atomistic materialism. According to this theory, matter is the fundamental principle of existent and ever-evolving reality, and it is constituted of atoms. But whereas for the first atomists atoms were not so much a substance (ousia) as an ideal form (idea) through which they could explain sensible bodies and their movement, with Epicurus atoms effectively turned into a substance. From a mathematical theory we come to a physical conception.