Now the doctrine of sensibility is at the same time the doctrine of the noumenon in the negative sense,.e., of things that the understanding must think without this relation to our kind of intuition, thus not merely as appearances but as things in themselves, but about which, however, it also understands that in this abstractionb it cannot consider making any use of its categories, since they have significance only in relation to the unity of intuitions in space and time, and can even determine this unity a priori through general concepts of combination only on account of the mere ideality of space and time.