Lucretius, The Nature of Things
Background on Lucretius (Britannica)
Summary
Lucretius states that everything is made out of atoms, and that no atom could come into existence or leave off existing. However, in everything there is also some of the void. The void is simply empty space, and it is what allows things to be hard or soft. The void also enables movement. Atoms can only move because there is empty space to move into. Also, he says that atoms are unbreakable. He argues that if there was not something that was totally unbreakable–namely atoms–then everything could be infinitely divisible, and everything would decay down to nothing. Then, Lucretius tackles and debunks other theories of existence, including homoeomery. He talks about how atoms interact and come together, saying that atoms come in many different shapes and sizes, and it is these different kinds of atoms coming together that enable every different kind of substance. In fact, he says that every substance contains some amount of every kind of atom.