It was then properly the _Understanding_ which has its special realm in the _cognitive faculty_, so far as it contains constitutive principles of cognition _a priori_, which by the Critique, comprehensively called the Critique of pure Reason, was to be placed in certain and sole possession[8] against all other competitors. And so also to _Reason_, which contains constitutive principles _a priori_ nowhere except simply in respect of the _faculty of desire_, should be assigned its place in the Critique of practical Reason. Whether now the _Judgement_, which in the order of our cognitive faculties forms a mediating link between Understanding and Reason, has also principles _a priori_ for itself; whether these are constitutive or merely regulative (thus indicating no special realm); and whether they give a rule _a priori_ to the feeling of pleasure and pain, as the mediating link between the cognitive faculty and the faculty of desire (just as the Understanding prescribes laws _a priori_ to the first, Reason to the second); these are the questions with which the present Critique of Judgement is concerned. A Critique of pure Reason, _i.e._ of our faculty of judging _a priori_ according to principles, would be incomplete, if the Judgement, which as a cognitive faculty also makes claim to such principles, were not treated as a particular part of it; although its principles in a system of pure Philosophy need form no particular part between the theoretical and the practical, but can be annexed when needful to one or both as occasion requires. For if such a system is one day to be completed under the general name of Metaphysic (which it is possible to achieve quite completely, and which is supremely important for the use of Reason in every reference), the soil for the edifice must be explored by Criticism as deep down as the foundation of the faculty of principles independent of experience, in order that it may sink in no part, for this would inevitably bring about the downfall of the whole. We can easily infer from the nature of the Judgement (whose right use is so necessarily and so universally requisite, that by the name of sound Understanding nothing else but this faculty is meant), that it must be attended with great difficulties to find a principle peculiar to it; (some such it must contain _a priori_ in itself, for otherwise it would not be set apart by the commonest Criticism as a special cognitive faculty). This principle must not be derived _a priori_ from concepts, for these belong to the Understanding, and Judgement is only concerned with their application. It must, therefore, furnish of itself a concept, through which, properly speaking, no thing is cognised, but which only serves as a rule, though not an objective one to which it can adapt its judgement; because for this latter another faculty of Judgement would be requisite, in order to be able to distinguish whether [any given case] is or is not the case for the rule.