Critique of Pure Reason

by Immanuel Kant

  There must therefore be something to make this reproduction of phenomena possible by being itself the foundation a priori of a necessary synthetical unity of them. This becomes clear if we only remember that all phenomena are not things by themselves, but only the play of our representations, all of which are in the end determinations only of the internal sense. If therefore we could prove that even our purest intuitions a priori give us no knowledge, unless they contain such a combination of the manifold as to render a constant synthesis of reproduction possible, it would follow that this synthesis of the imagination is, before all experience, founded on principles a priori, and that we must admit a pure transcendental synthesis of imagination which forms even the foundation of the possibility of all experience, such experience being impossible without the reproductibility of phenomena. Now, when I draw a line in thought, or if I think the time from one noon to another, or if I only represent to myself a certain number, it is clear that I must first necessarily apprehend one of these manifold representations after another. If I were to lose from my thoughts what precedes, whether the first parts of a line or the antecedent portions of time, or the numerical unities representing one after the other, and if, while I proceed to what follows, I were unable to reproduce what came before, there would never be a complete representation, and none of the before-mentioned thoughts, not even the first and purest representations of space and time, could ever arise within us.

  The synthesis of apprehension is therefore inseparably connected with the synthesis of reproduction, and as the former constitutes the transcendental ground of the possibility of all knowledge in general (not only of empirical, but also of pure a priori knowledge), it follows that a reproductive synthesis of imagination belongs to the transcendental acts of the soul. We may therefore call this faculty the transcendental faculty of imagination.

  III

  Of the Synthesis of Recognition in Concepts

  Without our being conscious that what we are thinking now is the same as what we thought a moment before, all reproduction in the series of representations would be vain. Each representation would, in its present state, be a new one, and in no wise belonging to the act by which it was to be produced by degrees, and the manifold in it would never form a whole, because deprived of that unity which consciousness alone can impart to it. If in counting I forget that the unities which now present themselves to my mind have been added gradually one to the other, I should not know the production of the quantity by the successive addition of one to one, nor should I know consequently the number, produced by the counting, this number being a concept consisting entirely in the consciousness of that unity of synthesis.

  The very word of concept (Begriff) could have suggested this remark, for it is the one consciousness which unites the manifold that has been perceived successively, and afterwards reproduced into one representation. This consciousness may often be very faint, and we may connect it with the effect only, and not with the act itself, i.e. with the production of a representation. But in spite of this, that consciousness, though deficient in pointed clearness, must always be there, and without it, concepts, and with them, knowledge of objects are perfectly impossible.

  And here we must needs arrive at a clear understanding of what we mean by an object of representations. We said before that phenomena are nothing but sensuous representations, which therefore by themselves must not be taken for objects outside our faculty of representation. What then do we mean if we speak of an object corresponding to, and therefore also different from our knowledge? It is easy to see that such an object can only be conceived as something in general=x: because, beside our knowledge, we have absolutely nothing which we could put down as corresponding to that knowledge.

  Now we find that our conception of the relation of all knowledge to its object contains something of necessity, the object being looked upon as that which prevents our knowledge from being determined at haphazard, and causes it to be determined a priori in a certain way, because, as they are all to refer to an object, they must necessarily, with regard to that object, agree with each other, that is to say, possess that unity which constitutes the concept of an object.

  It is clear also that, as we can only deal with the manifold in our representations, and as the x corresponding to them (the object), since it is to be something different from all our representations, is really nothing to us, it is clear, I say, that the unity, necessitated by the object, cannot be anything but the formal unity of our consciousness in the synthesis of the manifold in our representations. Then and then only do we say that we know an object, if we have produced synthetical unity in the manifold of intuition. Such unity is impossible, if the intuition could not be produced, according to a rule, by such a function of synthesis as makes the reproduction of the manifold a priori necessary, and a concept in which that manifold is united, possible. Thus we conceive a triangle as an object, if we are conscious of the combination of three straight lines, according to a rule, which renders such an intuition possible at all times. This unity of rule determines the manifold and limits it to conditions which render the unity of apperception possible, and the concept of that unity is really the representation of the object = x, which I think, by means of the predicates of a triangle.

  No knowledge is possible without a concept, however obscure or imperfect it may be, and a concept is always, with regard to its form, something general, something that can serve as a rule. Thus the concept of body serves as a rule to our knowledge of external phenomena, according to the unity of the manifold which is thought by it. It can only be such a rule of intuitions because representing, in any given phenomena, the necessary reproduction of their manifold elements, or the synthetical unity in our consciousness of them. Thus the concept of body, whenever we perceive something outside us, necessitates the representation of extension, and, with it, those of impermeability, shape, etc.

  Necessity is always founded on transcendental conditions. There must be therefore a transcendental ground of the unity of our consciousness in the synthesis of the manifold of all our intuitions, and therefore also a transcendental ground of all concepts of objects in general, and therefore again of all objects of experience, without which it would be impossible to add to our intuitions the thought of an object, for the object is no more than that something of which the concept predicates such a necessity of synthesis.

  That original and transcendental condition is nothing else but what I call transcendental apperception. The consciousness of oneself, according to the determinations of our state, is, with all our internal perceptions, empirical only, and always transient. There can be no fixed or permanent self in that stream of internal phenomena. It is generally called the internal sense, or the empirical apperception. What is necessarily to be represented as numerically identical with itself, cannot be thought as such by means of empirical data only. It must be a condition which precedes all experience, and in fact renders it possible, for thus only could such a transcendental supposition acquire validity.

  No knowledge can take place in us, no conjunction or unity of one kind of knowledge with another, without that unity of consciousness which precedes all data of intuition, and without reference to which no representation of objects is possible. This pure, original, and unchangeable consciousness I shall call transcendental apperception. That it deserves such a name may be seen from the fact that even the purest objective unity, namely, that of the concepts a priori (space and time), is possible only by a reference of all intuitions to it. The numerical unity of that apperception therefore forms the a priori condition of all concepts, as does the manifoldness of space and time of the intuitions of the senses.

  The same transcendental unity of apperception constitutes, in all possible phenomena which may come together in our experience, a connection of all these representations according to laws. For that unity of consciousness would be impossible, if the mind, in the knowledge of the manifold, could not become conscious of the identity of functio
n, by which it unites the manifold synthetically in one knowledge. Therefore the original and necessary consciousness of the identity of oneself is at the same time a consciousness of an equally necessary unity of the synthesis of all phenomena according to concepts, that is, according to rules, which render them not only necessarily reproducible, but assign also to their intuition an object, that is, a concept of something in which they are necessarily united. The mind could never conceive the identity of itself in the manifoldness of its representations (and this a priori) if it did not clearly perceive the identity of its action, by which it subjects all synthesis of apprehension (which is empirical) to a transcendental unity, and thus renders its regular coherence a priori possible. When we have clearly perceived this, we shall be able to determine more accurately our concept of an object in general. All representations have, as representations, their object, and can themselves in turn become objects of other representations. The only objects which can be given to us immediately are phenomena, and whatever in them refers immediately to the object is called intuition. These phenomena, however, are not things in themselves, but representations only which have their object, but an object that can no longer be seen by us, and may therefore be called the not-empirical, that is, the transcendental object, = x.

  The pure concept of such a transcendental object (which in reality in all our knowledge is always the same = x) is that which alone can give to all our empirical concepts a relation to an object or objective reality. That concept cannot contain any definite intuition, and can therefore refer to that unity only, which must be found in the manifold of our knowledge, so far as it stands in relation to an object. That relation is nothing else but a necessary unity of consciousness, and therefore also of the synthesis of the manifold, by a common function of the mind, which unites it in one representation. As that unity must be considered as a priori necessary (because, without it, our knowledge would be without an object), we may conclude that the relation to a transcendental object, that is, the objective reality of our empirical knowledge, rests on a transcendental law, that all phenomena, if they are to give us objects, must be subject to rules a priori of a synthetical unity of these objects, by which rules alone their mutual relation in an empirical intuition becomes possible: that is, they must be subject, in experience, to the conditions of the necessary unity of apperception quite as much as, in mere intuition, to the formal conditions of space and time. Without this no knowledge is possible.

  IV

  Preliminary Explanation of the Possibility of the Categories as Knowledge a priori

  There is but one experience in which all perceptions are represented as in permanent and regular connection, as there is but one space and one time in which all forms of phenomena and all relations of being or not being take place. If we speak of different experiences, we only mean different perceptions so far as they belong to one and the same general experience. It is the permanent and synthetical unity of perceptions that constitutes the form of experience, and experience is nothing but the synthetical unity of phenomena according to concepts.

  Unity of synthesis, according to empirical concepts, would be purely accidental, nay, unless these were founded on a transcendental ground of unity, a whole crowd of phenomena might rush into our soul, without ever forming real experience. All relation between our knowledge and its objects would be lost at the same time, because that knowledge would no longer be held together by general and necessary laws; it would therefore become thoughtless intuition, never knowledge, and would be to us the same as nothing.

  The conditions a priori of any possible experience in general are at the same time conditions of the possibility of any objects of our experience. Now I maintain that the categories of which we are speaking are nothing but the conditions of thought which make experience possible, as much as space and time contain the conditions of that intuition which forms experience. These categories therefore are also fundamental concepts by which we think objects in general for the phenomena, and have therefore a priori objective validity. This is exactly what we wish to prove.

  The possibility, nay the necessity of these categories rests on the relation between our whole sensibility, and therefore all possible phenomena, and that original apperception in which everything must be necessarily subject to the conditions of the permanent unity of self-consciousness, that is, must submit to the general functions of that synthesis which we call synthesis according to concepts, by which alone our apperception can prove its permanent and necessary identity a priori. Thus the concept of cause is nothing but a synthesis of that which follows in temporal succession, with other phenomena, but a synthesis according to concepts: and without such a unity which rests on a rule a priori, and subjects all phenomena to itself, no permanent and general, and therefore necessary unity of consciousness would be formed in the manifold of our perceptions. Such perceptions would then belong to no experience at all, they would be without an object, a blind play of representations,—less even than a dream.

  All attempts therefore at deriving those pure concepts of the understanding from experience, and ascribing to them a purely empirical origin, are perfectly vain and useless. I shall not dwell here on the fact that a concept of cause, for instance, contains an element of necessity, which no experience can ever supply, because experience, though it teaches us that after one phenomenon something else follows habitually, can never teach us that it follows necessarily, nor that we could a priori, and without any limitation, derive from it, as a condition, any conclusion as to what must follow. And thus I ask with reference to that empirical rule of association, which must always be admitted if we say that everything in the succession of events is so entirely subject to rules that nothing ever happens without something preceding it on which it always follows,—What does it rest on, if it is a law of nature, nay, how is that very association possible? You call the ground for the possibility of the association of the manifold, so far as it is contained in the objects themselves, the affinity of the manifold. I ask, therefore, how do you make that permanent affinity by which phenomena stand, nay, must stand, under permanent laws, conceivable to yourselves?

  According to my principles it is easily conceivable. All possible phenomena belong, as representations, to the whole of our possible self-consciousness. From this, as a transcendental representation, numerical identity is inseparable and a priori certain, because nothing can become knowledge except by means of that original apperception. As this identity must necessarily enter into the synthesis of the whole of the manifold of phenomena, if that synthesis is to become empirical knowledge, it follows that the phenomena are subject to conditions a priori to which their synthesis (in apprehension) must always conform. The representation of a general condition according to which something manifold can be arranged (with uniformity) is called a rule, if it must be so arranged, a law. All phenomena therefore stand in a permanent connection according to necessary laws, and thus possess that transcendental affinity of which the empirical is a mere consequence.

  It sounds no doubt very strange and absurd that nature should have to conform to our subjective ground of apperception, nay, be dependent on it, with respect to her laws. But if we consider that what we call nature is nothing but a whole of phenomena, not a thing by itself, but a number of representations in our soul, we shall no longer be surprised that we only see her through the fundamental faculty of all our knowledge, namely, the transcendental apperception, and in that unity without which it could not be called the object (or the whole) of all possible experience, that is, nature. We shall thus also understand why we can recognise this unity a priori, and therefore as necessary, which would be perfectly impossible if it were given by itself and independent of the first sources of our own thinking. In that case I could not tell whence we should take the synthetical propositions of such general unity of nature. They would have to be taken from the objects of nature themselves, and as this could be done empirically only, we could derive from it none but an a
ccidental unity, which is very different from that necessary connection which we mean when speaking of nature.

  Deduction of the Pure Concepts of the Understanding

  Section III

  Of the Relation of the Understanding to Objects in General and the Possibility of Knowing Them a priori,

  What in the preceding section we have discussed singly and separately we shall now try to treat in connection with each other and as a whole. We saw that there are three subjective sources of knowledge on which the possibility of all experience and of the knowledge of its objects depends, namely, sense, imagination, and apperception. Each of them may be considered as empirical in its application to given phenomena; all, however, are also elements or grounds a priori which render their empirical application possible. Sense represents phenomena empirically in perception, imagination in association (and reproduction), apperception in the empirical consciousness of the identity of these reproductive representations with the phenomena by which they were given; therefore in recognition.