Speaking generally, seeing that the definition consists of genus and differentiae, if the definition of the contrary term is apparent, the definition of the term before you will be apparent also; for since its contrary is found either in the same genus or in the contrary genus, and likewise also the differentiae predicated of opposites are either contrary or the same, clearly of the term before you there will be predicated either the same genus as of its contrary, while, of its differentiae, either all are contrary to those of its contrary, or at least some of them are so while the rest remain the same; or, vice Some scholars see a reference to Posterior Analytics.