Chapter 37

All things that fall in the same category are generically the same (as man and horse). Generically different are all those that fall in different categories (as animal and knowledge). They are different in genus. On the other hand, all things that come under the same species and thus have their substance in common, as Peter and Paul, are specifically the same. But those are specifically different which differ from one another in species, that is to say, by reason of their substance, as do man and the horse. All those things are numerically different which by the combination of their accidents have marked off for themselves the individuality of their own individual substance and have thus acquired individual existence, that is to say, those that are individuals, such as Peter and Paul and all other individual men.

The differences of all things that are generically different are also specifically different, as, for example, those of animal and knowledge—for the animal comes under substance, whereas knowledge comes under quality. Constituent differences of the animal are the animate and the sentient, whereas the rational, the irrational, the winged, the terrestrial, or the aquatic are dividing differences. On the other hand, constituent differences of knowledge are its inherence in animate rational beings and, besides this, its tendency to inalterability; whereas grammar and philosophy are dividing differences. For to that category to which the genus belongs the species also belongs, and so also do the differences of the species. And nothing prevents the same differences from belonging to the subaltern genera and species, but not all, because, for example, the living cannot make the non-living. Now, by differences here I mean those which constitute the genera and the species.

Moreover, one should know that the nine categories which are not substance, even though they are accidents, do each one have constituent and dividing differences. Each is a most general genus and each has subaltern species and genera and most specific species. For, without exception, where there is a genus, there there are species and dividing differences, since they are what divide the genera into species. And where there are species, there there are differences also, for they are what constitute the species.