Immanuel Kant's Critique of Pure Reason — trans. F. Max Müller

I have only touched on these questions in order to leave no gap in what are commonly supposed to be the concepts of the understanding. But absolute possibility (which has no regard for the formal conditions of experience) is really no concept of the understanding, and can never be used empirically, but belongs to reason alone, which goes beyond all possible empirical use of the understanding. We have therefore made these few critical remarks only, leaving the subject itself unexplained for the present.

And here, when I am on the point of concluding this fourth number and at the same time the system of all principles of the pure understanding, I think I ought to explain why I call the principles of modality postulates. I do not take this term in the sense which has [p. 233] been given to it by some modern philosophical writers, and which is opposed to the sense in which mathematicians take it, viz. that to postulate should mean to represent a proposition as certain without proof or justification ; for if we were to admit with regard to synthetical propositions, however evident they may appear, that they should meet with unreserved applause, without any deduction, and on their own authority only, all criticism of the understanding would be at an end. And as there is no lack of bold assertions, which public opinion does not decline to accept, (this acceptance being, however, no credential), our understanding would be open to every fancy, and could not refuse its sanction to claims which demand admission as real axioms in the same confident tone, though without any substantial reasons. If therefore a condition a priori is to be synthetically joined to the concept of a thing, it will be indispensable that, if not a proof, at least a deduc1 90 T^'anscendental Analytic 2tion of the legitimacy of such an assertion, should be. forthcoming.

The principles of modality, however, are not objectively synthetical, because the predicates of possibility, reality, and necessity do not in the least increase the concept of which they are predicated, by adding anything to its representation. But as nevertheless they are synthetical, they are so subjectively only, i.e. they add to the [p. 234] concept of a (real) thing, without predicating anything new, the peculiar faculty of knowledge from which it springs and on which it depends, so that, if in the understanding the concept is only connected with the formal conditions of experience, its object is called possible ; if it is connected with perception (sensation as the material of the senses), and through it determined by the understanding, its object is called real ; while, if it is determined through the connection of perceptions, according to concepts, its object is called necessary. The principles of modality therefore predicate nothing of a concept except the act of the faculty of knowledge by which it is produced. In mathematics a postulate means a practical proposition, containing nothing but a synthesis by which we first give an object to ourselves and produce its concept, as if, for instance, we draw a circle with a given line from a given point in the plane. Such a proposition cannot be proved, because the process required for it is the very process by which we first produce the concept of such a figure. We may therefore with the same right postulate the principles of modality, because they never increase^ the concept of a thing, but indicate the manner