It would certainly be more satisfactory to our speculative reason if it could solve these problems for itself without this circuit and preserve the solution for practical use as a thing to be referred to, but in fact our faculty of speculation is not so well provided. Those who boast of such high knowledge ought not to keep it back, but to exhibit it publicly that it may be tested and appreciated. They want to prove: very good, let them prove; and the critical philosophy lays its arms at their feet as the victors. Quid statis? Nolint. Atqui licet esse beatis. As they then do not in fact choose to do so, probably because they cannot, we must take up these arms again in order to seek in the mortal use of reason, and to base on this, the notions of God, freedom, and immortality, the possibility of which speculation cannot adequately prove. Here first is explained the enigma of the critical philosophy, viz.: how we deny objective reality to the supersensible use of the categories in speculation and yet admit this reality with respect to the objects of pure practical reason. This must at first seem inconsistent as long as this practical use is only nominally known. But when, by a thorough analysis of it, one becomes aware that the reality spoken of does not imply any theoretical determination of the categories and extension of our knowledge to the supersensible; but that what is meant is that in this respect an object belongs to them, because either they are contained in the necessary determination of the will a priori, or are inseparably connected with its object; then this inconsistency disappears, because the use we make of these concepts is different from what speculative reason requires. On the other hand, there now appears an unexpected and very satisfactory proof of the consistency of the speculative critical philosophy. For whereas it insisted that the objects of experience as such, including our own subject, have only the value of phenomena, while at the same time things in themselves must be supposed as their basis, so that not everything supersensible was to be regarded as a fiction and its concept as empty; so now practical reason itself, without any concert with the speculative, assures reality to a supersensible object of the category of causality, viz., freedom, although (as becomes a practical concept) only for practical use; and this establishes on the evidence of a fact that which in the former case could only be conceived. By this the strange but certain doctrine of the speculative critical philosophy, that the thinking subject is to itself in internal intuition only a phenomenon, obtains in the critical examination of the practical reason its full confirmation, and that so thoroughly that we should be compelled to adopt this doctrine, even if the former had never proved it at all. * {PREFACE ^paragraph 10}