That it is not susceptible of proof is clear because (as concept of a natural product) it embraces in itself natural necessity, and at the same time (as purpose) a contingency of the form of the Object (in reference to the mere laws of nature) in the very same thing. Hence, if there is to be no contradiction here it must contain a ground for the possibility of the thing in nature, and also a ground of the possibility of this nature itself and of its reference to something which, not being empirically cognisable nature (supersensible), is therefore for us not cognisable at all. [This is requisite] if it is to be judged according to a different kind of causality from that of natural mechanism when we wish to establish its possibility.

The concept of a thing, then, as a natural