Again dipping into Russell's History of Western Philosophy, Russell writes that:
Aristotle advances against the theory of ideas a number of very good arguments... The strongest is that of the 'third man': if a man is a man because he resembles an ideal man, there must be a still more ideal man to whom both ordinary man and the ideal man are similar.
A problem with applying logic to gibberish is that gibberish is intrinsically illogical, but anyway...
Take the idea that 'A man is a man because he resembles an ideal man.' The only sensible portion of this is the first two words, 'a man.' It is ludicrous to say a man is a man, or a chair is a chair; the very words 'a man' or 'a chair' establish the fact of its existence as itself. And as for 'a man is a man because...'; if Plato had said: 'A man is a man because he is a man' - idiotic though it would be it would still cling to some kind of sense, but unfortunately Plato departs even from this modicum of reason and instead decides a man is a man because he resembles something else that is not a man - an ideal man, that is, an idea of a man.
So Plato's line, to be a little more clear, should read, 'A man is a man because he resembles an idea in his own head, and this idea in his own head is an idea in his own head because it is conceived of by a man, namely himself.'
He might as well say, 'A man is a man because he resembles a horse.' And at least a horse indubitably exists; you can point to one, whereas all one can point to with the words 'the ideal man' are those very words. That is as far as their independent life extends, and remove an actual man and those words remove themselves as an obvious matter of course, since words cannot exist independently of their user.
At this point Aristotle enters the arena and says that for some reason or other there would have to be a more ideal man than the ideal man. Whatever implications this is supposed to have, Aristotle, and presumably Russell, have failed to notice that 'ideal' denotes an absolute. It means a state of perfection. It makes no sense to talk of something being more ideal than an ideal, more perfect than perfection; and so Aristotle's Third Man, who is more ideal than the ideal, is merely linguistic nonsense.