The Theory of Forms: what are the Forms?

Plato, answered from the texts and cited to the page.

The position in brief

The Forms are eternal, unchanging eide — paradigms of which sensible things are imperfect imitations. Beauty Itself, Justice Itself, the Good Itself; the Forms are the proper objects of episteme while sensibles are objects only of doxa. The position developed across the dialogues. In the Phaedo and Republic the Forms are strongly metaphysical — separately existing, knowable through dialectic, the cause of the being of sensibles.

In the Parmenides I subjected the doctrine to self-critique: the Third Man argument poses a real difficulty (if Beauty Itself is a Form because it is beautiful, and the beautiful Form requires another Form to explain its beauty, an infinite regress threatens). The late Sophist works with a modified theory in terms of the communion of kinds — Forms partake of one another, Same and Different and Being weave through the rest. The position is not static.¹²

Sources

1. THEAET. Very true. srR. Yes, we have gone through only a small part of them, and they are, if I may say so, infinite. -THEAET. Ît would, apparently, be impossible to catch the sophist, if that is the case. srr. Well, then, shall we weaken and give up the struggle now? THEAET. No, Î say; we must not do that, if we can in any way get the slightest hold of the fellow. srr.

   Sophist, pp. 46–48

2. ' Socrates," he said, ' what an admirable talent for argument you have! Tell me, did you invent this distinction yourself, which separates abstract ideas from the things which partake of them? And do you think there is such à thing as abstract likeness apart from the likeness which we possess, and abstract one and many, and the other abstractions of which you heard Zeno speaking just now?

   Parmenides, pp. 7–9

Where the argument is made

• Phaedo 65d-66a, 74a-75d (the equality argument), 100b-105e
• Republic V 476a-480a (Forms vs sensibles), VI 506b-509c (the sun analogy), VII 514a-518b (the cave)
• Parmenides 130a-135c (the Third Man and other self-critiques)
• Sophist 247e-258e (the communion of kinds, Forms in late form)
• Symposium 210a-212a (the ascent to the Form of Beauty)

How the argument was received

The central Plato metaphysical question and the most worked- over in the scholarly tradition. Cornford defended the strong-metaphysical middle-period reading; Cherniss the unitarian continuity; Owen the rigor of the Third Man; Vlastos a Forms-as-criteria reading; Aristotle's Metaphysics rejects the separate existence of the Forms. The interpretive difficulty is genuine; the texts do not fully resolve.