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.**The union of causality as freedom with causality as rational mechanism, the former established by the moral law, the latter by the law of nature in the same subject, namely, man, is impossible, unless we conceive him with reference to the former as a being in himself, and with reference to the latter as a phenomenon- the former in pure consciousness, the latter in empirical consciousness.
Otherwise reason inevitably contradicts itself.
By this also I can understand why the most considerable objections which I have as yet met with against the Critique turn about these two points, namely, on the one side, the objective reality of the categories as applied to noumena, which is in the theoretical department of knowledge denied, in the practical affirmed; and on the other side, the paradoxical demand to regard oneself qua subject of freedom as a noumenon, and at the same time from the point of view of physical nature as a phenomenon in one's own empirical consciousness; for as long as one has formed no definite notions of morality and freedom, one could not conjecture on the one side what was intended to be the noumenon, the basis of the alleged phenomenon, and on the other side it seemed doubtful whether it was at all possible to form any notion of it, seeing that we had previously assigned all the notions of the pure understanding in its theoretical use exclusively to phenomena.Nothing but a detailed criticism of the practical reason can remove all this misapprehension and set in a clear light the consistency which constitutes its greatest merit.
So much by way of justification of the proceeding by which, in this work, the notions and principles of pure speculative reason which have already undergone their special critical examination are, now and then, again subjected to examination.This would not in other cases be in accordance with the systematic process by which a science is established, since matters which have been decided ought only to be cited and not again discussed.In this case, however, it was not only allowable but necessary, because reason is here considered in transition to a different use of these concepts from what it had made of them before.Such a transition necessitates a comparison of the old and the new usage, in order to distinguish well the new path from the old one and, at the same time, to allow their connection to be observed.Accordingly considerations of this kind, including those which are once more directed to the concept of freedom in the practical use of the pure reason, must not be regarded as an interpolation serving only to fill up the gaps in the critical system of speculative reason (for this is for its own purpose complete), or like the props and buttresses which in a hastily constructed building are often added afterwards; but as true members which make the connexion of the system plain, and show us concepts, here presented as real, which there could only be presented problematically.This remark applies especially to the concept of freedom, respecting which one cannot but observe with surprise that so many boast of being able to understand it quite well and to explain its possibility, while they regard it only psychologically, whereas if they had studied it in a transcendental point of view, they must have recognized that it is not only indispensable as a problematical concept, in the complete use of speculative reason, but also quite incomprehensible; and if they afterwards came to consider its practical use, they must needs have come to the very mode of determining the principles of this, to which they are now so loth to assent.The concept of freedom is the stone of stumbling for all empiricists, but at the same time the key to the loftiest practical principles for critical moralists, who perceive by its means that they must necessarily proceed by a rational method.For this reason I beg the reader not to pass lightly over what is said of this concept at the end of the Analytic.
