| 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. |
| So long as we have not intuition we cannot know whether we do really think an object by the categories, and where an object can anywhere be found to cohere with them, and thus the truth is established, that the categories are not in themselves cognitions, but mere forms of thought for the construction of cognitions from given intuitions. |
| For the same reason is it true that from categories alone no synthetical proposition can be made. |
| For example; "In every existence there is substance," that is, something that can exist only as a subject and not as mere predicate; or, "Everything is a quantity"--to construct propositions such as these, we require something to enable us to go out beyond the given conception and connect another with it. |
| For the same reason the attempt to prove a synthetical proposition by means of mere conceptions, for example; "Everything that exists contingently has a cause," has never succeeded. |
| We could never get further than proving that, without this relation to conceptions, we could not conceive the existence of the contingent, that is, could not a priori through the understanding cognize the existence of such a thing; but it does not hence follow that this is also the condition of the possibility of the thing itself that is said to be contingent. |
| If, accordingly; we look back to our proof of the principle of causality, we shall find that we were able to prove it as valid only of objects of possible experience, and, indeed, only as itself the principle of the possibility of experience, Consequently of the cognition of an object given in empirical intuition, and not from mere conceptions. |
| That, however, the proposition; "Everything that is contingent must have a cause," is evident to every one merely from conceptions, is not to be denied. |
| But in this case the conception of the contingent is cogitated as involving not the category of modality (as that the non-existence of which can be conceived) but that of relation (as that which can exist only as the consequence of something else), and so it is really an identical proposition; "That which can exist only as a consequence, has a cause." In fact, when we have to give examples of contingent existence, we always refer to changes, and not merely to the possibility of conceiving the opposite.* But change is an event, which, as such, is possible only through a cause, and considered per se its non-existence is therefore possible, and we become cognizant of its contingency from the fact that it can exist only as the effect of a cause. |
| Hence, if a thing is assumed to be contingent, it is an analytical proposition to say, it has a cause. |
| [*Footnote; We can easily conceive the non-existence of matter; but the ancients did not thence infer its contingency. |
| But even the alternation of the existence and non-existence of a given state in a thing, in which all change consists, by no means proves the contingency of that state--the ground of proof being the reality of its opposite. |
| For example, a body is in a state of rest after motion, but we cannot infer the contingency of the motion from the fact that the former is the opposite of the latter. |
| For this opposite is merely a logical and not a real opposite to the other. |
| If we wish to demonstrate the contingency of the motion, what we ought to prove is that, instead of the motion which took place in the preceding point of time, it was possible for the body to have been then in rest, not, that it is afterwards in rest; for in this case, both opposites are perfectly consistent with each other.] |
| But it is still more remarkable that, to understand the possibility of things according to the categories and thus to demonstrate the objective reality of the latter, we require not merely intuitions, but external intuitions. |
| If, for example, we take the pure conceptions of relation, we find that (1) for the purpose of presenting to the conception of substance something permanent in intuition corresponding thereto and thus of demonstrating the objective reality of this conception, we require an intuition (of matter) in space, because space alone is permanent and determines things as such, while time, and with it all that is in the internal sense, is in a state of continual flow; (2) in order to represent change as the intuition corresponding to the conception of causality, we require the representation of motion as change in space; in fact, it is through it alone that changes, the possibility of which no pure understanding can perceive, are capable of being intuited. |