For these concepts serve partly to restrain the officious pretensions of understanding, which, presuming on its ability to supply a priori the conditions of the possibility of all things which it is capable of knowing, behaves as if it had thus determined these bounds as those of the possibility of all things generally, and partly also to lead understanding, in its study of nature, according to a principle of completeness, unattainable as this remains for it, and so to promote the ultimate aim of all knowledge.