Both Democritus and Anaxagoras try to explain the puzzling behaviour of ordinary reality by appeal to a microscopic replica of reality, in which another set of tiny bodies or minute scraps of stuff move around and cause things to happen. As a way to overcome the difficulty of explaining changes in the world, this ultimately emerges as unsatisfying: if there were problems with explaining chemical and physical events as they appear to us, there will be the same problems with explaining the reactions between smaller and yet smaller bodies.

Presocratic Philosophy: A Very Short Introduction (2004) - Ch. 4 : Reality and appearance: more adventures in metaphysics