Although, then, Philosophy can be divided only into two main parts, the theoretical and the practical, and although all that we may be able to say of the special principles of Judgement must be counted as belonging in it to the theoretical part, _i.e._ to rational cognition in accordance with natural concepts; yet the Critique of pure Reason, which must decide all this, as regards the possibility of the system before undertaking it, consists of three parts; the Critique of pure Understanding, of pure Judgement, and of pure Reason, which faculties are called pure because they are legislative _a priori_.
IV. OF JUDGEMENT AS A FACULTY LEGISLATING _A PRIORI_
Judgement in general is the faculty of thinking the particular as contained under the Universal. If the universal (the rule, the principle, the law) be given, the Judgement which subsumes the particular under it (even if, as transcendental Judgement, it furnishes _a priori_, the conditions in conformity with which subsumption under that universal is alone possible) is _determinant_. But if only the particular be given for which the universal has to be found, the Judgement is merely _reflective_.
The determinant Judgement only subsumes under universal transcendental laws given by the Understanding; the law is marked out for it, _a priori_, and it has therefore no need to seek a law for itself in order to be able to subordinate the particular in nature to the universal.--But the forms of nature are so manifold, and there are so many modifications of the universal transcendental natural concepts left undetermined by the laws given, _a priori_, by the pure Understanding,--because these only concern the possibility of a nature in general (as an object of sense),--that there must be laws for these [forms] also. These, as empirical, may be contingent from the point of view of _our_ Understanding, and yet, if they are to be called laws (as the concept of a nature requires), they must be regarded as necessary in virtue of a principle of the unity of the manifold, though it be unknown to us.--The reflective Judgement, which is obliged to ascend from the particular in nature to the universal, requires on that account a principle that it cannot borrow from experience, because its function is to establish the unity of all empirical principles under higher ones, and hence to establish the possibility of their systematic subordination. Such a transcendental principle, then, the reflective Judgement can only give as a law from and to itself. It cannot derive it from outside (because then it would be the determinant Judgement); nor can it prescribe it to nature, because reflection upon the laws of nature adjusts itself by nature, and not nature by the conditions according to which we attempt to arrive at a concept of it which is quite contingent in respect of these.