The Kantian categories constitute a complete, necessary system of concepts and thus lead to comprehension. These concepts constitute the form of connection between the concepts that occur in all empirical knowledge. To make a table of pure concepts, a distinction was made between the pure elementary concepts of the sensibility and those of the understanding. The former are space and time. The latter are the pure concepts or categories. The list is complete, necessary, and certain because it is based on a principle or rule. This principle is that thinking in general is judging. A table of the functions of judgments, when applied to objects in general, becomes a table of pure concepts of the understanding. These concepts, and only these, are our whole knowledge of things by pure understanding.