Full Idea
Some philosophers treat that is which not by making the logical point that that which is not is - not without qualification, but just that it is a thing which is not.
Gist of Idea
Some philosophers say that in some qualified way non-existent things 'are'
Source
Aristotle (Metaphysics [c.324 BCE], 1030a22)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.180
A Reaction
He is mainly refer to the mature works of Plato, especially 'Parmenides', in which he seems to have been mesmerised by that problem of referring to what doesn't exist. Key question: is there more than one way to 'exist'?