Full Idea
It is not true to say that what is not, since it is thought about, is something that is; for what is thought about it is not that it is, but that it is not.
Gist of Idea
Non-existent things aren't made to exist by thought, because their non-existence is part of the thought
Source
Aristotle (On Interpretation [c.330 BCE], 21a31)
Book Reference
Aristotle: 'Categories and De Interpretatione', ed/tr. Ackrill,J.R. [OUP 1963], p.59
A Reaction
At least there has been one philosopher who was quite clear about the distinction between a thought and what the thought is about (its content). Often forgotten!