Here then I end my whole critical undertaking. I shall proceed without delay to the doctrinal [part] in order to profit, as far as is possible, by the more favourable moments of my increasing years. It is obvious that in this [part] there will be no special section for the Judgement, because in respect of this faculty Criticism serves instead of Theory; but, according to the division of Philosophy (and also of pure Philosophy) into theoretical and practical, the Metaphysic of Nature and of Morals will complete the undertaking. INTRODUCTION I. OF THE DIVISION OF PHILOSOPHY We proceed quite correctly if, as usual, we divide Philosophy, as containing the principles of the rational cognition of things by means of concepts (not merely, as logic does, principles of the form of thought in general without distinction of Objects), into _theoretical_ and _practical_. But then the concepts, which furnish their Object to the principles of this rational cognition, must be specifically distinct; otherwise they would not justify a division, which always presupposes a contrast between the principles of the rational cognition belonging to the different parts of a science. Now there are only two kinds of concepts, and these admit as many distinct principles of the possibility of their objects, viz. _natural concepts_ and the _concept of freedom_. The former render possible _theoretical_ cognition according to principles _a priori_; the latter in respect of this theoretical cognition only supplies in itself a negative principle (that of mere contrast), but on the other hand it furnishes fundamental propositions which extend the sphere of the determination of the will and are therefore called practical. Thus Philosophy is correctly divided into two parts, quite distinct in their principles; the theoretical part or _Natural Philosophy_, and the practical part or _Moral Philosophy_ (for that is the name given to the practical legislation of Reason in accordance with the concept of freedom). But up to the present a gross misuse of these expressions has prevailed, both in the division of the different principles and consequently also of Philosophy itself. For what is practical according to natural concepts has been identified with the practical according to the concept of freedom; and so with the like titles, ‘theoretical’ and ‘practical’ Philosophy, a division has been made, by which in fact nothing has been divided (for both parts might in such case have principles of the same kind).