Full Idea
All methods employed to demonstrate the Forms either cannot be formulated validly, or produce Forms even for those things for which there are not supposed to be any Forms.
Gist of Idea
All attempts to prove the Forms are either invalid, or prove Forms where there aren't supposed to be any
Source
Aristotle (Metaphysics [c.324 BCE], 1079a04)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.402