Full Idea
If you accept the theory of Forms, you must allow that there is also another more powerful principle. Only thus can you answer the question why something has come to participate, or is participating.
Gist of Idea
If you accept Forms, you must accept the more powerful principle of 'participating' in them
Source
Aristotle (Metaphysics [c.324 BCE], 1075b18)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.387