  Concepts are, roughly, the units or elements of thoughts. In the Theaetetus (189e), a dialogue written after the Republic and Phaedo, Plato contends that thought is the silent dialogue of the soul with itself. If we can read back from this dialogue to the epistemology of the middle period, concepts are conceptual analogues to the subjects and predicates of spoken statements: corresponding to the predicate ‘equal’ of a statement such as ‘The sticks are equal’ is the concept [equality]. To debate whether there are ordinary versus philosophical concepts of [equality] thus invites consideration of how to distinguish concepts from one another. Basic in the Phaedo is that we have knowledge of Equality; that we perceive sensible equal objects, that we compare these sensible equals with the Form, and that in order to do this we must have had prior knowledge of Equality. Now, one question is whether the same concept applies both to the Form and the particulars. Whereas we moderns often focus on synonymy to distinguish co-referential concepts, issues of reference dominate Plato's thoughts. By the end of the Final Argument, it is clear that in a strict or primary fashion the concept/term is applied to the Form and in an indirect manner it is applied to the many instances that fall under the Form. (Using the language of names, ‘equal’ is the name of Equality and the eponym of the many particular equal things. (Cf. 102bff) With respect to the concept of Equality, it is individuated by its relation to the Form of Equality and, at best, derivatively to the many  equals.[22]  What individuates concepts or names, is not what is in the head of speakers, but rather just their relation to Forms.