In the Posterior Analytics, Aristotle imposes some requirements on scientific propositions: (i) they must be susceptible of syllogistic articulation, (ii) they must have universal terms as subjects of predication and (iii) their subjects must be primary, i.e. they cannot “be said of a distinct underlying subject”. However, it is problematic to meet those three requirements together. If associated with the theory of predication in Categories, the requirement (iii) shall prescribe names or descriptions of individuals within the category of substance as (...) subjects of predication, which are primary insofar as they cannot play the logical role of predicate. Nevertheless, if the requirement (i) is satisfied, then the terms of scientific proposition would be able to perform the function of subject as well as of predicate since the rules of conversion and syllogistic moods presuppose the interchangeability among terms of predication. The requirement (ii), by its turn, withdraws all particular subjects from scientific propositions and a fortiori individual substances. We offer as a solution for the aforementioned dilemma the association of theses from the Posterior Analytics, not with the treatise Categories, but with the new ontology of predication emerged in the Metaphysics, which, by introducing the hylomorphic analysis of compound substances, admits primary and notwithstanding universal subjects of predication: the specific forms. (shrink)