Full Idea
If the object of a belief is what is not, the object of this belief is nothing; but if there is no object to a belief, then that is not belief at all.
Gist of Idea
How can a belief exist if its object doesn't exist?
Source
Plato (Theaetetus [c.364 BCE], 189a)
Book Reference
Plato: 'Theaetetus', ed/tr. Waterfield,Robin [Penguin 1987], p.95