Plato's so-called Theory of Forms
The fault, to my mind, with all attempts to deal with Plato’s so-called Theory of Forms is that they start from the assumption that Plato had such a completely worked-out theory. If that were the case, it would certainly be strange that so much study of and so much research in the works of one who could think so clearly and could write so lucidly would fail to arrive even at an outline of the putative theory.
As I see it, Plato (1) inherited Socrates’ distinction between the intelligible ideas and ideals found only in the mind, on the one hand, and the sensible world on the other hand; (2) extended the scope of these intelligibles first to the mathematical sphere and then beyond that; (3) found in these intelligibles the answer to the Heraclitean challenge to the possibility of knowledge; (4) experimented with various modes of stating how the intelligibles are related to the sensibles, none of which modes he found satisfactory as is clear from the first part of the Parmenides; (5) lost interest in the thankless quest but never lost his faith in the primacy of the intelligible realm as the sole ground and home of true epistêmê and of the mind as the fount and begetter of the intelligible and all intelligibility, of phronêsis and noêsis. This is the position I maintain in Plato: An Interpretation (2005).
Because Plato never worked out a completed Theory of Forms the attempt to extract such a theory from his works remains a Holy Grail quest.
D. R. Khashaba