Using categories to think about things in themselves does not yield knowledge of the nature or possibility of things in themselves

We can think of any objects whatsoever using the categories. In fact, this is unavoidable; the categories are the most basic concepts of objects in general, so we cannot think about anything whatsoever without using some categories to do so. But in thinking about the things in themselves using categories we do not thereby (a) know that there are things in themselves falling under the categories or (b) even that it is possible for there to be things in themselves falling under the categories. The