This paper is my first effort to revaluate the disagreement between two central texts for Aristotle's the conception of ousia: Categories and Metaphysics VII. Scholars have taken chapter Zeta-3 as a payment of the debt with the Categories, so that the hylomorphic analysis of the composite substance would require a revision of the subject-criterion, now improved by the addition of the “a this” and “separate” criterion. This paper, however, downgrades the importance of the Categories for understanding Aristotle's Metaphysics Z. The two texts are dealing with different arguments and are not incompatible with one another.
I myself consider this paper somehow obsolete, for I have returned to the same subject more than once: in my 2003 paper on Z-3 and, most importantly, on my Book 'As Noções Aristotélicas de Substância e Essência' (2008).