Full Idea
If there is the same Form for the Forms and for their participants, then they must have something in common.
Gist of Idea
If there is one Form for both the Form and its participants, they must have something in common
Source
comment on Plato (works [c.375 BCE]) by Aristotle - Metaphysics 991a
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.34