Plato's Parmenides III: Greater Difficulties

Parmenides now moves on to raise two stern objections to Socrates' theory of Forms. Edith Hamilton's translation has a very brief introduction to the dialogue in which she says that it is unclear why Plato wrote a dialogue that was so harshly critical of his own most cherished idea. It is "certainly a curious procedure since in the end he apparently neither demolishes them nor establishes them," she says, but "[t]o some people, however, it is only what is to be expected from Plato, never out to defend his own views, always with one object alone, to know the truth. It would be natrual for him to do his best to find out if what he had built up could be torn down."

Especially the second of these two objections will remain relevant in theology even to this day: in the Middle Ages, Maimonides and others were gravely concerned with the proof that God could not know us. 

Parmenides sets up his first objection with a reprise of his Third Man argument. If these Forms exist like ideas in a mind, then they are unlike the things in the world. The things in the world that are supposed to be 'made in their image' have extension in three dimensions, weight, color, and so forth; the forms are unextended objects, which cannot have parts (as per the last discussion). Thus, no Form is anything like the things for which it is supposed to be the model. 

A further proof that the Forms cannot be 'like' the things in the world is that, if they were, then there is room for a third concept that unifies the Form and the thing it is 'like.' You have the Form of a Table, say, and a bunch of actual tables; what holds those things together as a category? If the Form of a Table is an idea about the essential nature of a table, then it is the thing that holds all the tables together in a category. Yet if the Form of a Table is like the tables in some way, then another idea must exist that holds the Form together with the several tables. (The real objection is not that there must be a 'third' thing, but that the process will repeat infinitely, so that knowing any Form requires knowing an infinite number of higher Forms as well).

Now he gets to what he calls his "worst" objection to the Theory of Forms. If the Forms are supposed to be ideas that capture the real essence of a thing, then knowledge of them should be knowledge of the real things. Yet knowing a Form gives you no knowledge about the facts of the world. His (unfortunate) example is slavery: knowing the Form of Master and the Form of Slave doesn't tell you who is a slave; and even if you recognize a slave, it doesn't tell you who his master is. "The significance of things in our world is not with reference to things in that other world [i.e. the world of the Forms]." 

If that is true, the real and best kind of knowledge will be knowledge of a world so separate from ours that knowing the truth would provide us with no benefits. Our branches of knowledge, insofar as they exist in this world, would seem to involve knowledge of the real things -- not knowledge of the ideal things. 

This leads to the second objection, which is the one that bothered theologians. It would seem that "a god," and certainly God, would have the best kind of knowledge. Indeed, the usual way of talking about the Forms since the advent of Christianity is to talk about them as "Ideas in the Mind of God." So God, at least, knows the forms even if none of us do.

But because God knows the Forms, what God knows is not knowledge of this world but of the world of Forms. Later monotheistic theologians will prove to their satisfaction that God himself must be simple and unextended -- this is Aquinas' position, and Avicenna's, and Maimonides' -- and thus the Forms are the only things God could know, because they are simple and lack parts too. 

Even in Parmenides' day, the perfection of divine knowledge implied knowledge of the Forms rather than knowledge of particulars. 

Then if the most perfect mastership and most perfect knowledge are in the god's world, the gods' mastership can never be exercised over us, nor their knowledge know us or anything in our world. Just as we do not rule over them by virtue of rule as it exists in our world, and we know nothing that is divine by our knowledge, so they, on the same principle, being gods, are not our masters nor do they know anything of human concerns.

This is an intolerable objection in the eyes of the Christian philosophers especially, for whom a personal relationship with God is the essence of the faith. Yet it's also a problem for Jewish philosophers, for whom their foundational books are all about God knowing particular prophets and others, and working with them directly. 

(The Muslim philosophers seem unbothered by it; this would explain, e.g., why Allah communicated to Muhammad through an angel rather than directly. The angels serve a metaphysical role as messengers and intermediaries between the divine and the human. Avicenna's proofs of divine simplicity are thus thoroughgoing and unbothered by the fact that the consequence is that humans cannot have a direct relationship with such a God as he describes.)

Aristotle accepts these objections, and generally rejects separate Forms (with the exception of Unmoved Movers, as mentioned, whose role for him doesn't require them to know us). He has a totally different idea about how knowledge of the forms works. If you're interested, and you have a little more than an hour, here is the best philosopher working today on this subject explaining how he believes Aristotle's model works.

Plato's model is that the Forms do exist separately, in spite of these problems that Parmenides raises. We still have a lot of ground to cover, but at least now you understand some of the problems that Plato expects to have to overcome in order to maintain his position.