  The details of the argument are controversial. Is it meant to be generalizable across the board so that it would work for things that are not substances, for example, qualities like redness? Aristotle elsewhere says that the sweet is necessarily so (Metaph IV 5 1010b24–6). Must the opponent say something that names a natural kind? What if the opponent says “animal”, naming a genus rather than a species? What if the opponent says “goatstag”, something that does not exist? Does the distinction between “signifying” and “signifying about” necessarily lead to subjects that are individuals (for example, individual human beings or horses) and their properties? Here, we run into the issue of Aristotelian essentialism.