| I have merely mentioned these questions, that in treating of the conception of the understanding, there might be no omission of anything that, in the common opinion, belongs to them. |
| In reality, however, the notion of absolute possibility (possibility which is valid in every respect) is not a mere conception of the understanding, which can be employed empirically, but belongs to reason alone, which passes the bounds of all empirical use of the understanding. |
| We have, therefore, contented ourselves with a merely critical remark, leaving the subject to be explained in the sequel. |
| Before concluding this fourth section, and at the same time the system of all principles of the pure understanding, it seems proper to mention the reasons which induced me to term the principles of modality postulates. |
| This expression I do not here use in the sense which some more recent philosophers, contrary to its meaning with mathematicians, to whom the word properly belongs, attach to it--that of a proposition, namely, immediately certain, requiring neither deduction nor proof. |
| For if, in the case of synthetical propositions, however evident they may be, we accord to them without deduction, and merely on the strength of their own pretensions, unqualified belief, all critique of the understanding is entirely lost; and, as there is no want of bold pretensions, which the common belief (though for the philosopher this is no credential) does not reject, the understanding lies exposed to every delusion and conceit, without the power of refusing its assent to those assertions, which, though illegitimate, demand acceptance as veritable axioms. |
| When, therefore, to the conception of a thing an a priori determination is synthetically added, such a proposition must obtain, if not a proof, at least a deduction of the legitimacy of its assertion. |
| The principles of modality are, however, not objectively synthetical, for the predicates of possibility, reality, and necessity do not in the least augment the conception of that of which they are affirmed, inasmuch as they contribute nothing to the representation of the object. |
| But as they are, nevertheless, always synthetical, they are so merely subjectively. |
| That is to say, they have a reflective power, and apply to the conception of a thing, of which, in other respects, they affirm nothing, the faculty of cognition in which the conception originates and has its seat. |
| So that if the conception merely agree with the formal conditions of experience, its object is called possible; if it is in connection with perception, and determined thereby, the object is real; if it is determined according to conceptions by means of the connection of perceptions, the object is called necessary. |
| The principles of modality therefore predicate of a conception nothing more than the procedure of the faculty of cognition which generated it. |
| Now a postulate in mathematics is a practical proposition which contains nothing but the synthesis by which we present an object to ourselves, and produce the conception of it, for example--"With a given line, to describe a circle upon a plane, from a given point"; and such a proposition does not admit of proof, because the procedure, which it requires, is exactly that by which alone it is possible to generate the conception of such a figure. |
| With the same right, accordingly, can we postulate the principles of modality, because they do not augment* the conception of a thing but merely indicate the manner in which it is connected with the faculty of cognition. |
| [*Footnote; When I think the reality of a thing, I do really think more than the possibility, but not in the thing; for that can never contain more in reality than was contained in its complete possibility. |
| But while the notion of possibility is merely the notion of a position of thing in relation to the understanding (its empirical use), reality is the conjunction of the thing with perception.] |
| GENERAL REMARK ON THE SYSTEM OF PRINCIPLES. |
| It is very remarkable that we cannot perceive the possibility of a thing from the category alone, but must always have an intuition, by which to make evident the objective reality of the pure conception of the understanding. |
| Take, for example, the categories of relation. |
| How (1) a thing can exist only as a subject, and not as a mere determination of other things, that is, can be substance; or how (2), because something exists, some other thing must exist, consequently how a thing can be a cause; or how (3), when several things exist, from the fact that one of these things exists, some consequence to the others follows, and reciprocally, and in this way a community of substances can be possible--are questions whose solution cannot be obtained from mere conceptions. |
| The very same is the case with the other categories; for example, how a thing can be of the same sort with many others, that is, can be a quantity, and so on. |