Full Idea
The elimination of evil is impossible, Theodorus; there must always be some force ranged against good.
Gist of Idea
There must always be some force of evil ranged against good
Source
Plato (Theaetetus [c.364 BCE], 176a)
Book Reference
Plato: 'Theaetetus', ed/tr. Waterfield,Robin [Penguin 1987], p.72