Critique of Pure Reason

by Immanuel Kant

  This is the proper place for trying to account for the paradox, which must have struck everybody in our exposition of the form of the internal sense (§ 6, see p. 28); namely, how that sense represents to the consciousness even ourselves, not as we are by ourselves, but as we appear to ourselves, because we perceive ourselves only as we are affected internally. This seems to be contradictory, because we should thus be in a passive relation to ourselves; and for this reason the founders of the systems of psychology have preferred to represent the internal sense as identical with the faculty of apperception, while we have carefully distinguished the two.

  What determines the internal sense is the understanding, and its original power of connecting the manifold of intuition, that is, of bringing it under one apperception, this being the very ground of the possibility of the understanding. As in us men the understanding is not itself an intuitive faculty, and could not, even if intuitions were given in our sensibility, take them into itself, in order to connect, as it were, the manifold of its own intuition, the synthesis of the understanding, if considered by itself alone, is nothing but the unity of action, of which it is conscious without sensibility also, but through which the understanding is able to determine that sensibility internally, with respect to the manifold which may be given to it (the understanding) according to the form of its intuition. The understanding, therefore, exercises its activity, under the name of a transcendental synthesis of the faculty of imagination, on the passive subject to which it belongs as a faculty, and we are right in saying that the internal sense is affected by that activity. The apperception with its synthetical unity is so far from being identical with the internal sense, that, as the source of all synthesis, it rather applies, under the name of the categories, to the manifold of intuitions in general, that is, to objects in general before all sensuous intuition; while the internal sense, on the contrary, contains the mere form of intuition, but without any connection of the manifold in it, and therefore, as yet, no definite intuition, which becomes possible only through the consciousness of the determination of the internal sense by the transcendental act of the faculty of imagination (the synthetical influence of the understanding on the internal sense) which I have called the figurative synthesis.

  This we can always perceive in ourselves. We cannot think a line without drawing it in thought; we cannot think a circle without describing it; we cannot represent, at all, the three dimensions of space, without placing, from the same point, three lines perpendicularly on each other; nay, we cannot even represent time, except by attending, during our drawing a straight line (which is meant to be the external figurative representation of time) to the act of the synthesis of the manifold only by which we successively determine the internal sense, and thereby to the succession of that determination in it. It is really motion, as the act of the subject (not as the determination of an object18), therefore the synthesis of the manifold in space (abstraction being made of space, and our attention fixed on the act only by which we determine the internal sense, according to its form), which first produces the very concept of succession. The understanding does not, therefore, find in the internal sense such a connection of the manifold, but produces it by affecting the internal sense. It may seem difficult to understand how the thinking ego can be different from the ego which sees or perceives itself (other modes of intuition being at least conceivable), and yet identical with the latter as the same subject, and how, therefore, I can say: I, as intelligence and thinking subject, know myself as an object thought so far as being given to myself in intuition also, but like other phenomena, not as I am to the understanding, but only as I appear to myself. In reality, however, this is neither more nor less difficult than how I can be, to myself, an object, and, more especially, an object of intuition and of internal perceptions. But that this must really be so, can clearly be shown—if only we admit space to be merely a pure form of the phenomena of the external senses—by the fact that we cannot represent to ourselves time, which is no object of external intuition, in any other way than under the image of a line which we draw, a mode of representation without which we could not realise the unity of its dimension; or again by this other fact that we must always derive the determination of the length of time, or of points of time for all our internal perceptions, from that which is represented to us as changeable by external things, and have therefore to arrange the determinations of the internal sense as phenomena in time, in exactly the same way in which we arrange the determinations of the external senses in space. If, then, with regard to the latter, we admit that by them we know objects so far only as we are affected externally, we must also admit, with regard to the internal sense, that by it we only are, or perceive ourselves, as we are internally affected by ourselves, in other words, that with regard to internal intuition we know our own self as a phenomenon only, and not as it is by itself.19

  § 25

  In the transcendental synthesis, however, of the manifold of representations in general, and therefore in the original synthetical unity of apperception, I am conscious of myself, neither as I appear to myself, nor as I am by myself, but only that I am. This representation is an act of thought, not of intuition. Now, in order to know ourselves, we require, besides the act of thinking, which brings the manifold of every possible intuition to the unity of apperception, a definite kind of intuition also by which that manifold is given, and thus, though my own existence is not phenomenal (much less a mere illusion), yet the determination of my existence20 can only take place according to the form of the internal sense, and in that special manner in which the manifold, which I connect, is given in the internal intuition. This shows that I have no knowledge of myself as I am, but only as I appear to myself. The consciousness of oneself is therefore very far from being a knowledge of oneself, in spite of all the categories which constitute the thinking of an object in general, by means of the connection of the manifold in an apperception. As for the knowledge of an object different from myself I require, besides the thinking of an object in general (in a category), an intuition also, to determine that general concept, I require for the knowledge of my own self, besides consciousness, or besides my thinking myself, an intuition also of the manifold in me, to determine that thought. I exist, therefore, as such an intelligence, which is simply conscious of its power of connection, but with respect to the manifold that has to be connected, is subject to a limiting condition which is called the internal sense, according to which that connection can only become perceptible in relations of time, which lie entirely outside the concepts of the understanding. Such an intelligence, therefore, can only know itself as it appears to itself in an intuition (which cannot be intellectual and given by the understanding itself), and not as it would know itself, if its intuition were intellectual.

  § 26

  Transcendental Deduction of the Universally Possible Employment of the Pure Concepts of the Understanding in Experience

  In the metaphysical deduction of the categories their a priori origin was proved by their complete accordance with the general logical functions of thought, while in their transcendental deduction; we established their possibility as knowledge a priori of objects of an intuition in general (§ 20, 21). Now we have to explain the possibility of our knowing a priori, by means of the categories, whatever objects may come before our senses, and this not according to the form of their intuition, but according to the laws of their connection, and of our thus, as it were, prescribing laws to nature, nay, making nature possible. Unless they were adequate to that purpose, we could not understand how everything that may come before our senses must be subject to laws which have their origin a priori in the understanding alone.

  First of all, I observe that by the synthesis of apprehension I understand the connection of the manifold in an empirical intuition, by which perception, that is, empirical consciousness of it (as phenomenal), becomes possible.

  We have forms of the external as well as the internal intuition a priori, in our repres
entations of space and time: and to these the synthesis of the apprehension of the manifold in phenomena must always conform, because it can take place according to that form only. Time and space, however, are represented a priori, not only as forms of sensuous intuition, but as intuitions themselves (containing a manifold), and therefore with the determination of the unity of that manifold in them (see transcendental Æsthetic21). Therefore unity of the synthesis of the manifold without or within us, and consequently a connection to which everything that is to be represented as determined in space and time must conform, is given a priori as the condition of the synthesis of all apprehension simultaneously with the intuitions, not in them, and that synthetical unity can be no other but that of the connection of the manifold of any intuition whatsoever in an original consciousness, according to the categories, only applied to our sensuous intuition. Consequently, all synthesis, without which even perception would be impossible, is subject to the categories; and as experience consists of knowledge by means of connected perceptions, the categories are conditions of the possibility of experience, and valid therefore a priori also for all objects of experience.

  If, for instance, I raise the empirical intuition of a house, through the apprehension of the manifold contained therein, into a perception, the necessary unity of space and of external sensuous intuition in general is presupposed, and I draw, as it were, the shape of the house according to that synthetical unity of the manifold in space. But this very synthetical unity, if I make abstraction of the form of space, has its seat in the understanding, and is in fact the category of the synthesis of the homogeneous in intuition in general: that is, the category of quantity, to which that synthesis of apprehension, that is, the perception, must always conform.22

  Or if, to take another example, I perceive the freezing of water I apprehend two states (that of fluidity and that of solidity), and these as standing to each other in a relation of time. But in the time, which as internal intuition I make the foundation of the phenomenon, I represent to myself necessarily synthetical unity of the manifold, without which that relation could not be given as determined in an intuition (with reference to the succession of time). That synthetical unity, however, as a condition a priori, under which I connect the manifold of any intuition, turns out to be, if I make abstraction of the permanent form of my intuition namely, of time, the category of cause, through which, if I apply it to my sensibility, I determine everything that happens, according to its relation in time. Thus the apprehension in such an event, and that event itself considered as a possible perception, is subject to the concept of the relation of cause and effect. The same applies to all other cases.

  Categories are concepts which a priori prescribe laws to all phenomena, and therefore to nature as the sum total of all phenomena (natura materialiter spectata). The question therefore arises, as these laws are not derived from nature, nor conform to it as their model (in which case they would be empirical only), how we can understand that nature should conform to them, that is, how they can determine a priori the connection of the manifold in nature, without taking that connection from nature. The solution of that riddle is this.

  It is no more surprising that the laws of phenomena in nature must agree with the understanding and its form a priori, that is, with its power of connecting the manifold in general, than that the phenomena themselves must agree with the form of sensuous intuition a priori. For laws exist as little in phenomena themselves, but relatively only, with respect to the subject to which, so far as it has understanding, the phenomena belong, as phenomena exist by themselves, but relatively only, with respect to the same being so far as it has senses. Things by themselves would necessarily possess their conformity to the law, independent also of any understanding by which they are known. But phenomena are only representations of things, unknown as to what they may be by themselves. As mere representations they are subject to no law of connection, except that which is prescribed by the connecting faculty. Now that which connects the manifold of sensuous intuition is the faculty of imagination, which receives from the understanding the unity of its intellectual synthesis, and from sensibility the manifoldness of apprehension. Thus, as all possible perceptions depend on the synthesis of apprehension, and that synthesis itself, that empirical synthesis, depends on the transcendental, and, therefore, on the categories, it follows that all possible perceptions, everything in fact that can come to the empirical consciousness, that is, all phenomena of nature, must, so far as their connection is concerned, be subject to the categories. On these categories, therefore, nature (considered as nature in general) depends, as on the original ground of its necessary conformity to law (as natura formaliter spectata). Beyond the laws, on which nature in general, as a lawful order of phenomena in space and time depends, the pure faculty of the understanding is incapable of prescribing a priori, by means of mere categories, laws to phenomena. Special laws, therefore, as they refer to phenomena which are empirically determined, cannot be completely derived from the categories, although they are all subject to them. Experience must be super-added in order to know such special laws: while those other a priori laws inform us only with regard to experience in general, and what can be known as an object of it.

  § 27

  Results of this Deduction of the Concepts of the Understanding

  We cannot think any object except by means of the categories; we cannot know any subject that has been thought, except by means of intuitions, corresponding to those concepts. Now all our intuitions are sensuous, and this knowledge, so far as its object is given, is empirical. But empirical knowledge is experience, and therefore no knowledge a priori is possible to us, except of objects of possible experience only.23

  This knowledge, however, though limited to objects of experience, is not, therefore, entirely derived from experience, for both the pure intuitions and the pure concepts of the understanding are elements of knowledge which exist in us a priori. Now there are only two ways in which a necessary harmony of experience with the concepts of its objects can be conceived; either experience makes these concepts possible, or these concepts make experience possible. The former will not hold good with respect to the categories (nor with pure sensuous intuition), for they are concepts a priori, and therefore independent of experience. To ascribe to them an empirical origin, would be to admit a kind of generatio aequivoca. There remains, therefore, the second alternative only (a kind of system of the epigenesis of pure reason), namely, that the categories, on the part of the understanding, contain the grounds of the possibility of all experience in general. How they render experience possible, and what principles of the possibility of experience they supply in their employment on phenomena, will be shown more fully in the following chapter on the transcendental employment of the faculty of judgment.

  Some one might propose to adopt a middle way between the two, namely, that the categories are neither self-produced first principles a priori of our knowledge, nor derived from experience, but subjective dispositions of thought, implanted in us with our existence, and so arranged by our Creator that their employment should accurately agree with the laws of nature, which determine experience (a kind of system of preformation of pure reason). But, in that case, not only would there be no end of such an hypothesis, so that no one could know how far the supposition of predetermined dispositions to future judgments might be carried, but there is this decided objection against that middle course that, by adopting it, the categories would lose that necessity which is essential to them. Thus the concept of cause, which asserts, under a presupposed condition, the necessity of an effect, would become false, if it rested only on some subjective necessity implanted in us of connecting certain empirical representations according to the rule of causal relation. I should not be able to say that the effect is connected with the cause in the object (that is, by necessity), but only, I am so constituted that I cannot think these representations as connected in any other way. This is exactly what the sceptic most desires, fo
r in that case all our knowledge, resting on the supposed objective validity of our judgments, is nothing but mere illusion, nor would there be wanting people to say they know nothing of such subjective necessity (which can only be felt); and at all events we could not quarrel with anybody about what depends only on the manner in which his own subject is organised.

  Comprehensive View of this Deduction