Does Aristotle’s Differentia Presuppose the Genus It Differentiates?

There seems to be an inconsistency at the heart of Aristotle’s Metaphysics: a differentia is said both to presuppose its genus (in vii 12) and to be logically independent from it (in x 7). I argue that the relation of analogy resolves this inconsistency, restores the coherence of the concepts of differentia and species, and gives x 7 its rightful place in the development of the Metaphysics.