This paper explores some aspects of Aristotle’s notion of subject for predications. I examine the argument Aristotle develops in Posterior Analytics I.22, 83a1-14. I argue that the notion advanced by Aristotle in that argument is different from the one found in his Categories, although they are far from being incompatible with each other. I also add some philological considerations to justify the Portuguese translation of “hypokeimenon” as “algo subjacente” (“underlying thing”) instead of “sujeito” (“subject”).