What is an Ontological Category?

In this article, I examine the concept of a natural class and propose a definition of "ontological category" in terms of that concept. Let's say a class is "large" if its membership comprises a significant proportion of the things which are there. Let's say a class is "high" if it is not a proper subclass of any natural class. Then a natural class is a primary ontological category if and only if (a) there are large natural classes, and (b) it is a high class. (Secondary, tertiary, etc., ontological categories are defined by an extension of this definition). I defend the definition, consider various ways in which it might be modified, and apply it to the problem of constructing a taxonomy of ontologies.