In this paper I deal with a puzzling passage, which occurs in Metaphysics Z 13.1038b2 – 3 and where Aristotle mentions four possible meanings of substance: the substratum, the essence, the compound of these (τὸ ἐκ τούτων) and the universal. This list accords only partially with the previous one in Z 3.1028b33–36, where Aristotle mentions the substratum, the essence, the universal and the genus. Thus, Z 13’s list omits Z 3’s genus, but includes τὸ ἐκ τούτων, which is standardly used by Aristotle to refer to the compound of matter and form. This is puzzling, for at least two reasons: (1) it is not clear what has happened to Z 3’s genus; (2) it is not clear what exactly is the reference of τὸ ἐκ τούτων, for the context suggests, at first glance awkwardly, that the compound in question is that of substratum and essence, and not of matter and form. These problems have led some scholars to delete τὸ ἐκ τούτων from the list. In this paper I provide two sets of arguments in order to resist the deletion. In the first set I show how, at least in principle, it would not be inaccurate to define the compound of matter and form as a “compound of substratum and essence”. In the second set, I show how, in fact, through the reference to the compound of substratum and essence, Aristotle does not want to designate, in Z 13, the hylomorphic composite. Rather, he aims to designate the notion of form regarded as universal, namely as ‘species’, which seems to reveal a peculiar sort of composition between a substratum (its genus) and an essence (its specific difference).