The moral law, the law of obligation, thus proceeds from a source in man above reason. It is token of his membership as a moral being in a kingdom of absolute ends above nature. But it is also directed to something in man which is equally above nature: it appeals to and demands freedom. Reason is incapable of anything so irrational, so self-contradictory, as imposing a law of action to which no faculty of action corresponds. The freedom of the moral will is the answer to the unqualified demand of duty. It is not open to man to accept or reject this truth as he may see fit. It is a principle of reason which is involved in every exercise of reason. In denying it in name, man none the less acknowledges it in fact. Only men already sophisticated by vice who are seeking an excuse for their viciousness ever try to deny, even in words, the response which freedom makes to the voice of duty. Since, however, freedom is an absolute stranger to the natural and sensible world, man's possession of moral freedom is the final sign and seal of his membership in a supersensible world. The existence of an ideal or spiritual realm with its own laws is thus certified to by the fact of man's own citizenship within it. But, once more, this citizenship and this certification are solely moral. Scientific or intellectual warrant for it is impossible or self-contradictory, for science works by the law of causal necessity with respect to what is, ignorant of any law of freedom referring to what should be. With the doors to the supersensible world now open, it is but a short step to religion. Of the negative traits of true religion we may be sure in advance. It will not be based upon intellectual grounds. Proofs of the existence of God, of the creation of nature, of the existence of an immaterial soul from the standpoint of knowledge are all of them impossible. They transgress the limits of knowledge, since that is confined to the sensible world of time and space. Neither will true religion be based upon historic facts such as those of Jewish history or the life of Jesus or the authority of a historic institution like a church. For all historic facts as such fall within the realm of time which is sensibly conditioned. From the points of view of natural theology and historic religions Kant was greeted by his contemporaries as the "all-shattering." Quite otherwise is it, however, as to moral proofs of religious ideas and ideals. In Kant's own words: "I have found it necessary to deny knowledge of God, freedom and immortality in order to find a place for faith"--faith being a moral act.