BOOK IV.
Chapter 1
Our attention must now be directed to what appertains to genus, and property, and these are the elements of such as belong to definitions, but about them there is seldom a consideration by disputants. If then it should be laid down that there is a genus of any certain thing, we must first have respect to all things allied to what is spoken, whether it is not predicated of something, as is the case with accident, as if good is assumed as the genus of pleasure, (we must see) whether a certain pleasure is not good; for if this happens, it is clear that good is not the genus of pleasure, since genus is predicated of all things under the same species. Next, whether it is not predicated in answer to the question, what a thing is; but as accident, as whiteness, of snow, or what is moved by itself, of the soul; for neither is snow, the same thing as whiteness, wherefore whiteness, is not the genus of snow, nor is the soul, the same as what is moved, but it is accidental to it, to be moved, as also it frequently happens to an animal, to walk and to be walking. Moreover, the being moved, is not a certain thing, but appears to signify something active, or passive; likewise also whiteness, for it does not discover what snow is, but what kind of thing it is; hence neither of these, is predicated in reply to the question what a thing is.
Notwithstanding, we must especially have regard to the definition of accident, if it concurs with the stated genus, as also in what has just now been mentioned, for the same thing may possibly move, and not move itself, likewise also may be white, and not white, so that neither of these is genus, but accident, since we denominate that accident, which possibly may, and may not be present, with a certain thing.
