We hence see that a complex of practical precepts given by Philosophy does not constitute a distinct part of Philosophy, as opposed to the theoretical part, because these precepts are practical; for they might be that, even if their principles were derived altogether from the theoretical cognition of nature (as technically practical rules). [A distinct branch of Philosophy is constituted only] if their principle, as it is not borrowed from the natural concept, which is always sensuously conditioned, rests on the supersensible, which alone makes the concept of freedom cognisable by formal laws. These precepts are then morally practical, i.e. not merely precepts or rules in this or that aspect, but, without any preceding reference to purposes and designs, are laws.
II. OF THE REALM OF PHILOSOPHY IN GENERAL
So far as our concepts have a priori application, so far extends the use of our cognitive faculty according to principles, and with it Philosophy.
But the complex of all objects, to which those concepts are referred, in order to bring about a knowledge of them where it is possible, may be subdivided according to the adequacy or inadequacy of our [cognitive] faculty to this design.
Concepts, so far as they are referred to objects, independently of the possibility or impossibility of the cognition of these objects, have their field which is determined merely according to the relation that their Object has to our cognitive faculty in general. The part of this field in which knowledge is possible for us is a ground or territory (territorium) for these concepts and the requisite cognitive faculty. The part of this territory, where they are legislative, is the realm (ditio) of these concepts and of the corresponding cognitive faculties. Empirical concepts have, therefore, their territory in nature, as the complex of all objects of sense, but no realm, only a dwelling-place (domicilium); for though they are produced in conformity to law they are not legislative, but the rules based on them are empirical and consequently contingent.
Our whole cognitive faculty has two realms, that of natural concepts and that of the concept of freedom; for through both it is legislative a priori. In accordance with this, Philosophy is divided into theoretical and practical. But the territory to which its realm extends and in which its legislation is exercised, is always only the complex of objects of all possible experience, so long as they are taken for nothing more than mere phenomena; for otherwise no legislation of the Understanding in respect of them is conceivable.
Legislation through natural concepts is carried on by means of the Understanding and is theoretical. Legislation through the concept of freedom is carried on by the Reason and is merely practical. It is only in the practical [sphere] that the Reason can be legislative; in respect of theoretical cognition (of nature) it can merely (as acquainted with law by the Understanding) deduce from given laws consequences which always remain within [the limits of] nature. But on the other hand, Reason is not always therefore legislative, where there are practical rules, for they may be only technically practical.
Understanding and Reason exercise, therefore, two distinct legislations in regard to one and the same territory of experience, without prejudice to each other. The concept of freedom as little disturbs the legislation of nature, as the natural concept influences the legislation through the former.—The possibility of at least thinking without contradiction the co-existence of both legislations, and of the corresponding faculties in the same subject, has been shown in the Critique of pure Reason; for it annulled the objections on the other side by exposing the dialectical illusion which they contain.
These two different realms then do not limit each other in their legislation, though they perpetually do so in the world of sense. That they do not constitute one realm, arises from this, that the natural concept represents its objects in intuition, not as things in themselves, but as mere phenomena; the concept of freedom, on the other hand, represents in its Object a thing in itself, but not in intuition. Hence, neither of them can furnish a theoretical knowledge of its Object (or even of the thinking subject) as a thing in itself; this would be the supersensible, the Idea of which we must indeed make the basis of the possibility of all these objects of experience, but which we can never extend or elevate into a cognition.
There is, then, an unbounded but also inaccessible field for our whole cognitive faculty—the field of the supersensible—wherein we find no territory, and, therefore, can have in it, for theoretical cognition, no realm either for concepts of Understanding or Reason. This field we must indeed occupy with Ideas on behalf of the theoretical as well as the practical use of Reason, but we can supply to them in reference to the laws [arising] from the concept of freedom no other than practical reality, by which our theoretical cognition is not extended in the slightest degree towards the supersensible.
Now even if an immeasurable gulf is fixed between the sensible realm of the concept of nature and the supersensible realm of the concept of freedom, so that no transition is possible from the first to the second (by means of the theoretical use of Reason), just as if they were two different worlds of which the first could have no influence upon the second, yet the second is meant to have an influence upon the first. The concept of freedom is meant to actualise in the world of sense the purpose proposed by its laws, and consequently nature must be so thought that the conformity to law of its form, at least harmonises with the possibility of the purposes to be effected in it according to laws of freedom.—There must, therefore, be a ground of the unity of the supersensible, which lies at the basis of nature, with that which the concept of freedom practically contains; and the concept of this ground, although it does not attain either theoretically or practically to a knowledge of the same, and hence has no peculiar realm, nevertheless makes possible the transition from the mode of thought according to the principles of the one to that according to the principles of the other.
III. OF THE CRITIQUE OF JUDGEMENT AS A MEANS OF COMBINING THE TWO PARTS OF PHILOSOPHY INTO A WHOLE.
The Critique of the cognitive faculties, as regards what they can furnish a priori, has properly speaking no realm in respect of Objects, because it is not a doctrine, but only has to investigate whether and how, in accordance with the state of these faculties, a doctrine is possible by their means. Its field extends to all their pretensions, in order to confine them within their legitimate bounds. But what cannot enter into the division of Philosophy may yet enter, as a chief part, into the Critique of the pure faculty of cognition in general, viz. if it contains principles which are available neither for theoretical nor for practical use.
The natural concepts, which contain the ground of all theoretical knowledge a priori, rest on the legislation of the Understanding.—The concept of freedom, which contains the ground of all sensuously-unconditioned practical precepts a priori, rests on the legislation of the Reason. Both faculties, therefore, besides being capable of application as regards their logical form to principles of whatever origin, have also as regards their content, their special legislations above which there is no other (a priori); and hence the division of Philosophy into theoretical and practical is justified.
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