Front Page Titles (by Subject) SUPPLEMENT XXII - Critique of Pure Reason
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SUPPLEMENT XXII - Friedrich Max Müller, Critique of Pure Reason 
Immanuel Kant’s Critique of Pure Reason. In Commemoration of the Centenary of its First Publication. Translated into English by F. Max Mueller (2nd revised ed.) (New York: Macmillan, 1922).
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General Note on the System of the Principles
It is something very remarkable that we cannot understand the possibility of anything from the category alone, but must always have an intuition in order to exhibit by it the objective reality of the pure concept of the understanding. Let us take, for instance, the categories of relation. It is impossible to understand, from mere concepts alone: —
First, how something can exist as subject only, and not as a mere determination of other things, that is, how it can be a substance: or,
Secondly, how, because something is, something else must be, that is, how something can ever be a cause: or,
Thirdly, how, when there are several things, something could follow from the existence of one of them as affecting the rest, and vice versa, so that there should exist, in this way, a certain community of substances. The same applies to the other categories, as, for instance, how a thing could be of the same kind as many others, and thus be a quantity. So long as there is no intuition, we do not know whether by the categories we conceive an object, nay, whether any object can at all belong to them: and thus we see again that by themselves the categories are not knowledge, but mere forms of thought, by which given intuitions are turned into knowledge.
It likewise follows from this, that no synthetical proposition can be made out of mere categories, as, for instance, if it is said that in everything existing there is substance, i.e. something that can exist as subject only, and not as a mere predicate; or, everything is a quantum, etc. Here we have really nothing whatever which would enable us to go beyond a given concept, and to connect with it another. Hence no one has ever succeeded in proving a synthetical proposition by pure concepts of the understanding only: as, for instance, the proposition that everything which exists contingently, has a cause. All that could be proved was, that, without such a relation, we could not conceive the existence of what is contingent, that is, that we could not know a priori through the understanding the existence of such a thing; from which it does not follow in the least that the same condition applies to the possibility of things themselves. If the reader will go back to our proof of the principle of causality, he will perceive that we could prove it of objects of possible experience only, by saying that everything which happens (every event) presupposes a cause. We could prove it only as the principle of the possibility of experience, that is, of the knowledge of an object, given in empirical intuition, but not by means of mere concepts. It is perfectly true, that nevertheless this proposition, that everything contingent must have a cause, carries conviction to everybody from mere concepts: but it should be observed, that in this case the concept of the contingent contains no longer the category of modality (as something the non-existence of which can be conceived), but that of relation (as something which can only exist as the consequence of something else). It thus becomes in reality an identical proposition, namely, that that which can exist as a consequence only has its cause. And thus, when we have to give examples of contingent existence, we have always recourse to changes, and not only to the possibility of conceiving the opposite.1 Change, however, is an event which, as such, is possible through a cause only, and the non-existence of which is therefore possible in itself. We thus mean by contingency, that something can exist as the effect of a cause only; and if therefore a thing is assumed to be contingent, it becomes a merely analytical proposition to say that it has a cause.
It is still more remarkable, however, that, in order to understand the possibility of things according to the categories, and thus to establish the objective reality of the latter, we require not only intuitions, but always external intuitions. Thus, if we take, for instance, the pure concepts of relation, we find that: —
First, in order to give something permanent in intuition, corresponding to the concept of substance (and thus to show the objective reality of that concept), we require an intuition in space (of matter), because space alone can determine anything as permanent, while time, and therefore everything that exists in the internal sense, is in a constant flux.
Secondly, that in order to exhibit change, as the intuition corresponding to the concept of causality, we must use motion as change in space for our example, nay, can thus only gain an intuition of changes the possibility of which no pure understanding can ever conceive. Change is the connection of contradictory opposites in the existence of one and the same thing. Now, how it is possible that from a given state another state, opposed to it, should arise in the same thing, no reason can comprehend without an example; nay, without an intuition, cannot even render it intelligible to itself. That intuition, however, is that of the motion of a point in space, the presence of which in different places (as a consequence of opposite determinations) gives us, for the first time, an intuition of change: so that, in order to make even internal changes afterwards conceivable to ourselves, we must make time, as the form of the internal sense, figuratively comprehensible to ourselves by means of a line, and the internal change by means of the drawing of that line (motion): in other words, the successive existence of ourselves in different states, by means of an external intuition. The real reason of this lies in the fact that all change presupposes something permanent in intuition, in order that it may itself be perceived as change, while no permanent intuition is to be found in the internal sense.
Thirdly, and lastly, the category of community cannot, so far as its possibility is concerned, be conceived by mere reason alone: and the objective reality of that concept cannot therefore be possibly understood without intuition, and without external intuition in space. For how should we conceive the possibility that, when several substances exist, something (as an effect) could follow from the existence of one of them as affecting reciprocally the existence of the other, and that, therefore, because there is something in the former, something must also be in the latter, which, from the existence of the latter alone, could not be understood? For this is necessary to establish community, though it is utterly inconceivable among things, each of which completely isolates itself through its substantiality. Leibniz, therefore, as he attributed community to the substances of the world, as conceived by the understanding alone, required the interference of a Deity; because, as he justly perceived, such community would have been inconceivable from the existence of such substances only. We, on the contrary, can render the possibility of such a communion (of substances as phenomena) perfectly conceivable to ourselves, if we represent them to ourselves in space, that is, in external intuition. For space contains, even a priori, formal external relations, as conditions of the possibility of the real relations of action and reaction, that is, of community.
It is easy to show, in the same manner, that the possibility of things as quanta, and therefore, the objective reality of the category of quantity, can be exhibited in external intuition only, and, by means of it alone, be afterwards applied to the internal sense. But, in order to avoid prolixity, I must leave it to the reflection of the reader to find the examples of this.
The whole of these notes is of great importance, not only as confirming our previous refutation of idealism, but even more, when we come to treat of self-knowledge by mere internal consciousness, and the determination of our own nature, without the help of external empirical intuitions, in order to show us the limits of the possibility of such knowledge.
The last result of the whole of this section is therefore this: All principles of the pure understanding are nothing more than a priori principles of the possibility of experience; and to experience alone do all synthetical propositions a priori relate: nay, their possibility itself rests entirely on that relation.
[1 ]It is easy enough to conceive the non-existence of matter, but the ancients did not infer from this its contingency. Not even the change of being and not-being of any given state of a thing, which constitutes all change, can prove the contingency of that state, as if from the reality of its opposite. The rest of a body, for instance, following on its motion, does not yet prove the contingency of that motion, because the former is the opposite of the latter. The opposite here is opposed to the other, not realiter, but logically only. In order to prove the contingency of the motion of a body, we should have to prove that instead of the motion at the antecedent point of time, it would have been possible for the body to have been at rest at that very time, not that it is at rest afterwards; for in this case both opposites are quite consistent with each other.