They must.

And will not that of which the two partake, and which makes them alike, be
the idea itself?

Certainly.

Then the idea cannot be like the individual, or the individual like the
idea; for if they are alike, some further idea of likeness will always be
coming to light, and if that be like anything else, another; and new ideas
will be always arising, if the idea resembles that which partakes of it?

Quite true.

The theory, then, that other things participate in the ideas by
resemblance, has to be given up, and some other mode of participation
devised?

It would seem so.

Do you see then, Socrates, how great is the difficulty of affirming the
ideas to be absolute?

Yes, indeed.

And, further, let me say that as yet you only understand a small part of
the difficulty which is involved if you make of each thing a single idea,
parting it off from other things.

What difficulty? he said.