I'm really confused about the second paragraph. This is form Kenny's "A New History of Philosophy".
"One of the dysfunctional features of the doctrine of terms is that it fosters confusion between signs and what they signify. When Plato talks about nouns and verbs, he makes quite clear that he is talking about signs. He clearly distinguishes between the name ‘Theaetetus’ and the person Theaetetus whose name it is; and he is at pains to point out that the sentence ‘Theaetetus flies’ can occur even though what it tells us, namely the flying of Theaetetus, is not among the things there are in the world. It takes him some trouble to bring out the distinction between signs and signified, because of the lack of inverted commas in ancient Greek. This valuable device of modern languages makes it easy for us to distinguish the normal case where we are using a word to talk about what it signifies, and the special case in which we are mentioning a word to talk about the word itself, as in ‘ “Theaetetus” is a name’. The doctrine of terms, on the other hand, makes it all too easy to confuse use with mention.
Take a syllogism whose premisses are ‘Every human is mortal’, ‘Every Greek is human’. Shall we say, as Aristotle’s language sometimes suggests (e.g. APr. 1. 4. 25b37–9), that here mortal is predicated of human, and human is predicated of Greek? This does not seem quite right: what occurs as a predicate is surely a piece of language, and so perhaps we should say instead: ‘mortal’ is predicated of human and ‘human’ is predicated of Greek. But then we seem to have four terms, not three, in our syllogism, since ‘ “human”’ is not the same as ‘human’. We cannot remedy this by rephrasing the first proposition thus: ‘mortal’ is predicated of ‘human’. It is human beings themselves, not the words they use to refer to themselves, that are mortal. There is no doubt that Aristotle sometimes fell into confusion between use and mention; the wonder is that, given the quicksand provided by the doctrine of terms, he did not do so more often."
