Chapter 17

Predication of the essence of a thing is one thing, whereas that of its sort is another. Predication is of the essence of a thing when, being asked what a man is, we reply: ‘an animal.’ But it is of its sort when, being asked what sort of an animal, we answer: ‘a rational mortal animal.’ Thus, the genus and the species are predicated of the essence of a thing; whereas the difference, whether essential—that is to say, whether property or accident—is predicated of its sort. The individual substance neither signifies what the thing is nor of what sort it is, but it does signify which