Note 8 — Chapter XVII · THE EPICUREAN VIEWS ON NATURE.

(3) Atoms and empty space. With Democritus Epicurus agreed in holding that there is no other form of reality except that of bodily reality. Every substance, he says in the words of the Stoics, must affect others, and be affected by them; and whatever affects others or is itself affected, is corporeal. Corporeal substance is, therefore, the only kind of substance.8 The various qualities of things, essential as well as accidental qualities, are accordingly not incorporeal existences, but simply chance modes of body, the former being called by Epicurus συμβεβηκότα, the latter συμπτώματα.9 But a second something is necessary besides corporeal substance in order to explain phenomena, viz. empty space. That empty space exists is proved by the differences of weight in bodies. For what else could be the cause of this difference?10 It is proved still more conclusively by motion, motion being impossible without empty space.11 Mind as a moving cause, however, seems to Epicurus altogether superfluous. Everything that exists consists of bodies and empty space, and there is no third thing.12