According to the Greek Commentators in late antiquity, Aristotle's Categories is primarily concerned with simple expressions in so far as they signify things. But what is it for a simple expression to signify a thing? As for (non-empty) singular terms, it is safe to say that they denote things. But what about general terms? How do they signify things? The question is crucial to the theory of the Categories, since, as is argued in the first section of this paper, there is some truth in the Commentators' thesis that (part of) the Categories aims to elucidate the signification of simple expressions, including general terms. Of course, various prima facie plausible accounts of how general terms signify things are available; the second section discusses the basic assumptions which underlie them. A detailed analysis of Cat. 2a19-34 in the third section shows that the Categories' account is two-fold: On the one hand some general terms denote things (among the latter, the most prominent are τα κα' υπoκειμενoυ λεγoμενα). What is denoted by a given general term does not stand in any relation to the objects falling under the term but is something that they are. Some general terms, on the other hand, connote things. What is connoted by a general term is a property which the objects falling under the term are related to by virtue of having it (τα εν υπoκειμενω oντα are such properties).