The word ἀνόητα here is used in its ordinary sense, in which it is the negation, not of νοητός but of νοητικός. There is a similar confusion, Plato, Phædon, p. 80 B. Proklus (pp. 699-701, Stall.) is prolix but very obscure.
The Ideas are types or exemplars, and objects partake of them by being likened to them. Impossible.
4. Probably the case stands thus (says Sokrates). These Forms are constants and fixtures in nature, as models or patterns. Particular objects are copies or likenesses of them: and the participation of such objects in the Form consists in being made like to it.[16] In that case (replies Parmenides), the Form must itself be like to the objects which have been made like to it. Comparing the Form with the objects, that in which they resemble must itself be a Form: and thus you will have a higher Form above the first Form — and so upwards in the ascending line. This follows necessarily from the hypothesis that the Form is like the objects. The participation of objects in the Form, therefore, cannot consist in being likened to it.[17]
[16] Aristotle (Metaphys. A. 991, a. 20) characterises this way of presenting the Platonic Ideas as mere κενολογία and poetical metaphor. See also the remarkable Scholion of Alexander, pp. 574-575, Brandis.
[17] Plato, Parmenid. pp. 132-133.
This is again a repetition, though differently presented, of the same argument — ὁ τρίτος ἄνθρωπος — enunciated p. 132 A.
If Ideas exist, they cannot be knowable by us. We can know only what is relative to ourselves. Individuals are relative to individuals: Ideas relative to Ideas.
5. Here are grave difficulties (continues Parmenides) opposed to this doctrine of yours, affirming the existence of self-existent, substantive, unchangeable, yet participated, Forms. But difficulties still graver remain behind. Such Forms as you describe cannot be cognizable by us: at least it is hard to show how they can be cognizable. Being self-existent and substantive, they are not in us: such of them as are relative, have their relation with each other, not with those particular objects among us, which are called great, little, and so forth, from being supposed to be similar to or participant in the forms, and bearing names the same as those of the Forms. Thus, for example, if I, an individual man, am in the relation of master, I bear that relation to another individual man who is my servant, not to servantship in general (i.e. the Form of servantship, the Servus per se). My servant, again, bears the relation of servant to me, an individual man as master, — not to mastership in general (i.e. to the Form of mastership, the Dominus per se). Both terms of the relation are individual objects. On the other hand, the Forms also bear relation to each other. The Form of servantship (Servus per se) stands in relation to the Form of mastership (Dominus per se). Neither of them correlates with an individual object. The two terms of the relation must be homogeneous, each of them a Form.[18]
[18] Plato, Parmenid. p. 133 E.
Forms can be known only through the Form of Cognition, which we do not possess.