Now imagine that there are at one time three sensible F things, A, B, and C, each separate from each of the others.
Consider a plurality of F things, A, B, and C. By One-over-Many, each of A, B, C is F by virtue of partaking of a form of F-ness (say, F1).
By Self-Predication, F2 is F. Hence A, B, C, F1, and F2 are all F, and each is like the others in being F. Now consider the new plurality of F things, A, B, C, F1, and F2.
This thesis states necessary and sufficient conditions for something's being a member of some kind F such that all and only F things manifest the function characteristic of that kind.
By Self-Predication, F1 is F. Hence A, B, C and F1 are all F, and each is like the others in being F. Now consider the new plurality of F things, A, B, C, and F1.
From the existence of a plurality of F things and the fact that, for any such plurality P, there is a form of F-ness by virtue of partaking of which each member of P is F, it follows that there is one form "over" the many members of P (in the sense of being that by virtue of partaking of which each member of P is F).
In general, a Platonic Form F differs from an individual F thing in that F may be predicated univocally of the Form: The Form F is F.
One might be aware of the ordinary object as well as the F thing one is aware of.
It is not built into the meaning of "something appears F to one" that "one is aware of an F thing".
The point is that (i) and (ii) tell us that in an illusory experience one is aware of an F thing, but the ordinary object supposedly being perceived is not F, thus the F thing one is aware of and the ordinary object are not identical, by Leibniz's Law.
An individual F thing by comparison both is and is not F; in this sense the same property F can only be predicated equivocally of the individual (e.g. Republic 479a c).
