Testing the theory of forms › The greatest difficulty: can separated Forms be known?

Parmenides then introduces what he calls a greater difficulty. Forms that stand in relations to one another are taken to have those relations within their own domain. Corresponding things among us relate to one another within ours. His example is mastership and slavery: a particular human master is master of a particular human slave, while Mastership itself is related to Slavery itself (133b–134a).

The argument extends this restriction to knowledge. Knowledge itself would know truth itself, while the knowledge among us would concern the things among us. Given that separation of relational domains, our knowledge would not know the Forms. The question is therefore not simply whether we can see a nonphysical object. It concerns the additional assumption that the relevant relations remain confined to each domain (134a–c).

Parmenides presses a troubling consequence in the opposite direction. If the gods possess the most exact knowledge, and that knowledge belongs to the domain of Forms, then under the accepted relational restriction it would not know human affairs. The problem concerns divine knowers under those assumptions. It is not a claim that Forms themselves must be persons who know or fail to know us (134c–e).

This helps locate a possible response. A defender could distinguish independent existence from complete relational isolation. Something need not be created by our thought in order to be an object of our thought. But this defense must explain the bridge that the argument has prohibited. Merely repeating that the Forms are intelligible does not answer a challenge about the conditions under which they could be known.

The payoff for a reader is diagnostic. Whenever an explanation places its object beyond ordinary experience, ask what relation is still supposed to connect inquiry with it. That question alone does not refute the explanation. It identifies work the explanation owes us. The stronger claim that every independently existing object is unknowable would outrun the argument just examined.