Now if one can show that although the three kinds of transcendental ideas (psychological,a cosmological and theological) cannot be referred directly to any object corresponding to them and to its determination, and nevertheless that all rules of the empirical use of reason under the presupposition of such an object in the idea lead to systematic unity, always extending the cognition of experience but never going contrary to experience, then it is a necessary maxim of reason to proceed in accordance with such ideas.