 What then is Aristotle’s second classificatory system? Quite simply, it is a list of the highest kinds, which are also known as categories. That there are highest kinds (or perhaps that there is one single highest kind) can be motivated by noticing the fact that the ordinary objects of our experience fall into classes of increasing generality. Consider, for instance, a maple tree. It is in the first instance a maple and so belongs in a class with all and only other maples. It is also, however, a tree and so belongs in a broader class, namely the class of trees, whose extension is wider than the class of maples. Continuing on, it is also a living thing and so belongs in a class whose extension is wider still than the class of trees. And so on. Now, once this basic pattern is before us, we can ask the following question: does this increase in generality go on ad infinitum or does it end at a class that is the most general possible? Does it end, in other words, at a highest kind?