Critique of Pure Reason

by Immanuel Kant

  Supplement XXII

  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.28 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.

  Supplement XXIII

  In one word, none of these concepts admit of being authenticated, nor can their real possibility be proved, if all sensuous intuition (the only one which we possess) is removed, and there remains in that case a logical possibility only, that is, that a concept (a thought) is possible. This, however, does not c
oncern us here, but only whether the concept refers to an object and does therefore signify anything.

  Supplement XXIV

  We are met here by an illusion which is difficult to avoid. The categories do not depend in their origin on sensibility, like the forms of intuition, space, and time, and seem, therefore, to admit of an application extending beyond the objects of the senses. But, on the other side, they are nothing but forms of thought, containing the logical faculty only of comprehending a priori in one consciousness the manifold that is given in intuition, and they would therefore, if we take away the only intuition which is possible to us, have still less significance than those pure sensuous forms by which at least an object is given, while a peculiar mode of our understanding of connecting the manifold (unless that intuition, in which the manifold alone can be given, is added), signifies nothing at all.

  Nevertheless, it seems to follow from our very concept, if we call certain objects, as phenomena, beings of the senses, by distinguishing between the mode of our intuition and the nature of those objects by themselves, that we may take either the same objects in that latter capacity, though they cannot as such come before our intuition, or other possible things, which are not objects of our senses at all, and place them, as objects thought only by the understanding, in opposition to the former, calling them beings of the understanding (noumena). The question then arises, whether our pure concepts of the understanding do not possess some significance with regard to these so-called beings of the understanding, and constitute a mode of knowing them?

  At the very outset, however, we meet with an ambiguity which may cause great misapprehension. The understanding, by calling an object in one aspect a phenomenon only, makes to itself, apart from that aspect, another representation of an object by itself, and imagines itself able to form concepts of such an object. As, then, the understanding yields no other concepts but the categories, it supposes that the object in the latter aspect can be thought at least by those pure concepts of the understanding, and is thus induced to take the entirely indefinite concept of a being of the understanding, as of a something in general outside our sensibility, as a definite concept of a being which we might know to a certain extent through the understanding.

  If by noumenon we mean a thing so far as it is not an object of our sensuous intuition, and make abstraction of our mode of intuition, it may be called a noumenon in a negative sense. If, however, we mean by it an object of a non-sensuous intuition, we admit thereby a peculiar mode of intuition, namely, the intellectual, which, however, is not our own, nor one of which we can understand even the possibility. This would be the noumenon in a positive sense.

  The doctrine of sensibility is at the same time the doctrine of noumena in their negative sense; that is, of things which the understanding must think without reference to our mode of intuition, and therefore, not as phenomena only, but as things by themselves, but to which, after it has thus separated them, the understanding knows that it must not, in this new aspect, apply its categories; because these categories have significance only with reference to the unity of intuitions in space and time, and can therefore a priori determine that unity, on account of the mere ideality of space and time only, by means of general connecting concepts. Where that unity in time cannot be found, i.e. in the noumenon, the whole use, nay, the whole significance of categories comes to an end: because even the possibility of things that should correspond to the categories, would be unintelligible. On this point I may refer the reader to what I have said at the very beginning of the general note to the previous chapter (Suppl. XXII). The possibility of a thing can never be proved from the fact that its concept is not self-contradictory, but only by being authenticated by an intuition corresponding to it. If, therefore, we attempted to apply the categories to objects which are not considered as phenomena, we should have to admit an intuition other than the sensuous, and thus the object would become a noumenon in a positive sense. As, however, such an intuition, namely, an intellectual one, is entirely beyond our faculty of knowledge, the use of the categories also can never reach beyond the limits of the objects of experience. Beings of the understanding correspond no doubt to beings of the senses, and there may be beings of the understanding to which our faculty of sensuous intuition has no relation at all; but our concepts of the understanding, being forms of thought for our sensuous intuition only, do not reach so far, and what is called by us a noumenon must be understood as such in a negative sense only.

  Supplement XXV

  We must not speak, as is often done, of an intellectual world, for intellectual and sensitive apply to knowledge only. That, however, to which the one or the other mode of intuition applies, that is, the objects themselves, must, however harsh it may sound, be called intelligible or sensible.

  Supplement XXVI

  Metaphysic has for the real object of its investigations three ideas only, God, Freedom, and Immortality; the second concept connected with the first leading by necessity to the third as conclusion. Everything else treated by that science is a means only in order to establish those ideas and their reality. Metaphysic does not require these ideas for the sake of natural science; but in order to go beyond nature. A right insight into them would make theology, morality, and, by the union of both, religion also, therefore the highest objects of our existence, dependent on the speculative faculty of reason only, and on nothing else. In a systematical arrangement of those ideas the above order, being synthetical, would be the most appropriate; but in their elaboration, which must necessarily come first, the analytical or inverse order is more practical, enabling us, by starting from what is given us by experience, namely, the study of the soul (psychology), and proceeding thence to the study of the world (cosmology), and lastly, to a knowledge of God (theology), to carry out the whole of our great plan in its entirety.

  Supplement XXVII

  We shall therefore follow it with a critical eye through all the predicaments of pure psychology; but we shall, for the sake of brevity, let their examination proceed uninterruptedly.

  The following general remark may at the very outset make us more attentive to this mode of syllogism. I do not know any object by merely thinking, but only by determining a given intuition with respect to that unity of consciousness in which all thought consists; therefore, I do not know myself by being conscious of myself, as thinking, but only if I am conscious of the intuition of myself as determined with respect to the function of thought. All modes of self-consciousness in thought are therefore by themselves not yet concepts of understanding of objects (categories), but mere logical functions, which present no object to our thought to be known, and therefore do not present myself either as an object. It is not a consciousness of the determining, but only that of the determinable self, that is, of my internal intuition (so far as the manifold in it can be connected in accordance with the general condition of the unity of apperception in thought) which forms the object.

  1. In all judgments I am always the determining subject only of the relation which constitutes the judgment. That I, who think, can be considered in thinking as subject only, and as something not simply inherent in the thinking, as predicate, is an apodictical and even identical proposition; but it does not mean that, as an object, I am a self-dependent being or a substance. The latter would be saying a great deal, and requires for its support data which are not found in the thinking, perhaps (so far as I consider only the thinking subject as such) more than I shall ever find in it.

  2. That the Ego of apperception, and therefore the Ego in every act of thought, is a singular which cannot be dissolved into a plurality of subjects, and that it therefore signifies a logically simple subject, follows from the very concept of thinking, and is consequently an analytical proposition. But this does not mean that a thinking Ego is a simple substance, which would indeed be a synthetical proposition. The concept of substance always relates to intuitions which, with me, cannot be other but sensuous, and which therefore lie completely outside the f
ield of the understanding and its thinking, which alone is intended here, when we say that the Ego, in thinking, is simple. It would indeed be strange, if what elsewhere requires so great an effort, namely, to distinguish in what is given by intuition what is substance, and still more, whether that substance can be simple (as in the case of the component parts of matter), should in our case be given to us so readily in what is really the poorest of all representations, and, as it were, by an act of revelation.

  3. The proposition of the identity of myself amidst the manifold of which I am conscious, likewise follows from the concepts themselves, and is therefore analytical; but the identity of the subject of which, in all its representations, I may become conscious, does not refer to the intuition by which it is given as an object, and cannot therefore signify the identity of the person, by which is understood the consciousness of the identity of one's own substance, as a thinking being, in all the changes of circumstances. In order to prove this, the mere analysis of the proposition, I think, would avail nothing: but different synthetical judgments would be required, which are based on the given intuition.

  4. To say that I distinguish my own existence, as that of a thinking being, from other things outside me (one of them being my body) is likewise an analytical proposition; for other things are things which I conceive as different from myself. But, whether such a consciousness of myself is even possible without things outside me, whereby representations are given to me, and whether I could exist merely as a thinking being (without being a man), I do not know at all by that proposition.