What is being argued against Plato's theory of the forms in this passage (this is a dialogue):
Well, said Parmenides, and what do you say of another question? What question?
I imagine that the way in which you are led to assume one idea of each kind is as follows:—You see a number of great objects, and when you look at them there seems to you to be one and the same idea (or nature) in them all; hence you conceive of greatness as one.
Very true, said Socrates.
And if you go on and allow your mind in like manner to embrace in one view the idea of greatness and of great things which are not the idea, and to compare them, will not another greatness arise, which will appear to be the source of all these?
It would seem so.
Then another idea of greatness now comes into view over and above absolute greatness, and the individuals which partake of it; and then another, over and above all these, by virtue of which they will all be great, and so each idea instead of being one will be infinitely multiplied.