 At this point there appears to be a close connection between the essence of a substance and its species (eidos), and this might tempt one to suppose that Aristotle is identifying the substance of a thing (since the substance of a thing is its essence) with its species. (A consequence of this idea would be that Aristotle is radically altering his conception of the importance of the species, which in the Categories he called a secondary substance, that is, a substance only in a secondary sense.) But such an identification would be a mistake, for two reasons. First, Aristotle’s point at 1030a11 is not that a species is an essence, but that an essence of the primary kind corresponds to a species (e.g., man) and not to some more narrowly delineated kind (e.g., pale man). Second, the word ‘eidos’, which meant ‘species’ in the logical works, has acquired a new meaning in a hylomorphic context, where it means ‘form’ (contrasted with ‘matter’) rather than ‘species’ (contrasted with ‘genus’). In the conceptual framework of Metaphysics Ζ, a universal such as man or horse—which was called a species and a secondary substance in the Categories—is construed as “not substance but rather a compound of a sort, [consisting] of this account and this matter taken universally” (Ζ.10, 1035b29–30). The eidos that is primary substance in Book Ζ is not the species that an individual substance belongs to but the form that is predicated of the matter of which it is  composed.[4]