SOURCE: “Cosmology from Parmenides to Democritus,” in The Presocratics, Duckworth, 1972, pp. 127-48.

In the following excerpt, Hussey summarizes the atomistic theory and explains in what ways it was revolutionary.

The Atomists: Leucippus and Democritus

Of the life of Leucippus we know next to nothing, and there is little trustworthy information about that of Democritus. Both were citizens of Abdera, a small city on the northern shores of the Aegean, which like Elea had been founded by refugees from old Ionia. Democritus was perhaps the younger and, born like Socrates around 470, he lived on well into the fourth century.

Leucippus and Democritus were responsible for the Atomistic theory. Even though they were contemporaries of Socrates, their speculations are traditionally and reasonably grouped under the heading ‘Presocratic’, for the Atomistic theory is the last and greatest original effort in that kind of physical speculation which originated with the Milesians. The...