  The first group comprises what may be described roughly as extensional issues; they have to do with the number of categories. The extension of a term is comprised by the things of which the term can be truthfully predicated. Thus the extension of ‘cat’ consists of all the animals of which it is true to say that they are cats.  Philosophers in general frequently disagree on how many categories there are. For example, Aristotle lists up to ten, but gives the impression that the ultimate number is not settled at all. Plotinus (204/5–270) and Baruch Spinoza (1632–77) reduce the number radically, but their views do not by any means establish themselves as definitive.  In the Middle Ages the number of categories is always small (ten or less) but it nonetheless varies.