Immanuel Kant's Critique of Pure Reason, translated by Norman Kemp Smith





Section 1


JURISTS, when speaking of rights and claims, distinguish in a legal action the question of right (quid juris) from the question of fact (quid facti); and they demand that both be proved. Proof of the former, which has to state the right or the legal claim, they entitle the deduction. Many empirical concepts are employed without question from anyone. Since experience is always available for the proof of their objective reality, we believe ourselves, even without a deduction, to be justified in appropriating to them a meaning, an ascribed significance. But there are also usurpatory concepts, such as fortune, fate, which, though allowed to circulate by almost universal indulgence, are yet from time to time challenged by the question: quid juris. This demand for a deduction involves us in considerable perplexity, no clear legal title, sufficient to justify their employment, being obtainable either from experience or from reason.

Now among the manifold concepts which form the highly [121] complicated web of human knowledge, there are some which are marked out for pure a priori employment, in complete independence of all experience; and their right to be so employed always demands a deduction. For since empirical proofs do not suffice to justify this kind of employment, we are faced by the problem how these concepts can relate to objects which they yet do not obtain from any experience. The explanation of the manner in which concepts can thus relate a priori to objects I entitle their transcendental deduction; and from it I distinguish empirical deduction, which shows the manner in which a concept is acquired through experience and through reflection upon experience, and which therefore concerns, not its legitimacy, but only its de facto mode of origination.

We are already in possession of concepts which are of two quite different kinds, and which yet agree in that they relate to objects in a completely a priori manner, namely, the concepts of space and time as forms of sensibility, and the categories as concepts of understanding. To seek an empirical deduction of either of these types of concept would be labor entirely lost. For their distinguishing feature consists just in this, that they relate to their objects without having borrowed from experience anything that can serve in the representation of these objects. If, therefore, a deduction of such concepts is indispensable, it must in any case be transcendental.

We can, however, with regard to these concepts, as with regard to all knowledge, seek to discover in experience, if not the principle of their possibility, at least the occasioning causes of their production. The impressions of the senses supplying the first stimulus, the whole faculty of knowledge opens out to them, and experience is brought into existence. That experience contains two very dissimilar elements, namely, the matter of knowledge [obtained] from the senses, and a certain form for the ordering of this matter, [obtained] from the inner source of the pure intuition and thought which, on occasion of the sense-impressions, are first brought into action and yield concepts. Such an investigation of the first strivings of our faculty of knowledge, whereby it advances from particular perceptions to universal concepts, is undoubtedly of great service. We are indebted to the celebrated [122] Locke for opening out this new line of enquiry. But a deduction of the pure a priori concepts can never be obtained in this manner; it is not to be looked for in any such direction. For in view of their subsequent employment, which has to be entirely independent of experience, they must be in a position to show a certificate of birth quite other than that of descent from experiences. Since this attempted physiological derivation concerns a quaestio facti, it cannot strictly be called deduction; and I shall therefore entitle it the explanation of the possession of pure knowledge. Plainly the only deduction that can be given of this knowledge is one that is transcendental, not empirical. In respect to pure a priori concepts the latter type of deduction is an utterly useless enterprise which can be engaged in only by those who have failed to grasp the quite peculiar nature of these modes of knowledge.

But although it may be admitted that the only kind of deduction of pure a priori knowledge which is possible is on transcendental lines, it is not at once obvious that a deduction is indispensably necessary. We have already, by means of a transcendental deduction, traced the concepts of space and time to their sources, and have explained and determined their a priori objective validity. Geometry, however, proceeds with security in knowledge that is completely a priori, and has no need to beseech philosophy for any certificate of the pure and legitimate descent of its fundamental concept of space. But the concept is employed in this science only in its reference to the outer sensible world -- of the intuition of which space is the pure form -- where all geometrical knowledge, grounded as it is in a priori intuition, possesses immediate evidence. The objects, so far as their form is concerned, are given, through the very knowledge of them, a priori in intuition. In the case of the pure concepts of understanding, it is quite otherwise; it is with them that the unavoidable demand for a transcendental deduction, not only of themselves, but also of the concept of space, first originates. For since they speak of objects through predicates not of intuition and sensibility but of pure a priori thought, they relate to objects universally, [123] that is, apart from all conditions of sensibility. Also, not being grounded in experience, they cannot, in a priori intuition, exhibit any object such as might, prior to all experience, serve as ground for their synthesis. For these reasons, they arouse suspicion not merely in regard to the objective validity and the limits of their own employment, but owing to their tendency to employ the concept of space beyond the conditions of sensible intuition, that concept also they render ambiguous; and this, indeed, is why we have already found a transcendental deduction of it necessary. The reader must therefore be convinced of the unavoidable necessity of such a transcendental deduction before he has taken a single step in the field of pure reason. Otherwise he proceeds blindly, and after manifold wanderings must come back to the same ignorance from which he started. At the same time, if he is not to lament over obscurity in matters which are by their very nature deeply veiled, or to be too easily discouraged in the removal of obstacles, he must have a clear foreknowledge of the inevitable difficulty of the undertaking. For we must either completely surrender all claims to make judgments of pure reason in the most highly esteemed of all fields, that which transcends the limits of all possible experience, or else bring this critical enquiry to completion.

We have already been able with but little difficulty to explain how the concepts of space and time, although a priori modes of knowledge, must necessarily relate to objects, and how independently of all experience they make possible a synthetic knowledge of objects. For since only by means of such pure forms of sensibility can an object appear to us, and so be an object of empirical intuition, space and time are pure intuitions which contain a priori the condition of the possibility of objects as appearances, and the synthesis which takes place in them has objective validity.

The categories of understanding, on the other hand, do not represent the conditions under which objects are given in intuition. Objects may, therefore, appear to us without [124] their being under the necessity of being related to the functions of understanding; and understanding need not, therefore, contain their a priori conditions. Thus a difficulty such as we did not meet with in the field of sensibility is here presented, namely, how subjective conditions of thought can have objective validity, that is, can furnish conditions of the possibility of all knowledge of objects. For appearances can certainly be given in intuition independently of functions of the understanding. Let us take, for instance, the concept of cause, which signifies a special kind of synthesis, whereby upon something, A, there is posited something quite different, B, according to a rule. It is not manifest a priori why appearances should contain anything of this kind (experiences cannot be cited in its proof, for what has to be established is the objective validity of a concept that is a priori); and it is therefore a priori doubtful whether such a concept be not perhaps altogether empty, and have no object anywhere among appearances. That objects of sensible intuition must conform to the formal conditions of sensibility which lie a priori in the mind is evident, because otherwise they would not be objects for us. But that they must likewise conform to the conditions which the understanding requires for the synthetic unity of thought, is a conclusion the grounds of which are by no means so obvious. Appearances might very well be so constituted that the understanding should not find them to be in accordance with the Conditions of its unity. Everything might be in such confusion that, for instance, in the series of appearances nothing presented itself which might yield a rule of synthesis and so answer to the concept of cause and effect. This concept would then be altogether empty, null, and meaningless. But since intuition stands in no need whatsoever of the functions of thought, appearances would none the less present objects to our intuition.

If we thought to escape these toilsome enquiries by saying that experience continually presents examples of such regularity among appearances and so affords abundant opportunity of abstracting the concept of cause, and at the same time of verifying the objective validity of such a concept, we should be overlooking the fact that the concept of cause can [125] never arise in this manner. It must either be grounded completely a priori in the understanding, or must be entirely given up as a mere phantom of the brain. For this concept makes strict demand that something, A, should be such that something else, B, follows from it necessarily and in accordance with an absolutely universal rule. Appearances do indeed present cases from which a rule can be obtained according to which something usually happens, but they never prove the sequence to be necessary. To the synthesis of cause and effect there belongs a dignity which cannot be empirically expressed, namely that the effect not only succeeds upon the cause, but that it is posited through it and arises out of it. This strict universality of the rule is never a characteristic of empirical rules; they can acquire through induction only comparative universality, that is, extensive applicability. If we were to treat pure concepts of understanding as merely empirical products, we should be making a complete change in [the manner of] their employment.

Transition to the Transcendental Deduction of the Categories

There are only two possible ways in which synthetic representations and their objects can establish connection, obtain necessary relation to one another, and, as it were, meet one another. Either the object alone must make the representation possible, or the representation alone must make the object possible. In the former case, this relation is only empirical, and the representation is never possible a priori. This is true of appearances, as regards that [element] in them which belongs to sensation. In the latter case, representation in itself does not produce its object in so far as existence is concerned, for we are not here speaking of its causality by means of the will. None the less the representation is a priori determinant of the object, if it be the case that only through [126] the representation is it possible to know anything as an object. Now there are two conditions under which alone the knowledge of an object is possible, first, intuition, through which it is given, though only as appearance; secondly, concept, through which an object is thought corresponding to this intuition. It is evident from the above that the first condition, namely, that under which alone objects can be intuited, does actually lie a priori in the mind as the formal ground of the objects. All appearances necessarily agree with this formal condition of sensibility, since only through it can they appear, that is, be empirically intuited and given. The question now arises whether a priori concepts do not also serve as antecedent conditions under which alone anything can be, if not intuited, yet thought as object in general. In that case all empirical knowledge of objects would necessarily conform to such concepts, because only as thus presupposing them is anything possible as object of experience. Now all experience does indeed contain, in addition to the intuition of the senses through which something is given, a concept of an object as being thereby given, that is to say, as appearing. Concepts of objects in general thus underlie all empirical knowledge as its a priori conditions. The objective validity of the categories as a priori concepts rests, therefore, on the fact that, so far as the form of thought is concerned, through them alone does experience become possible. They relate of necessity and a priori to objects of experience, for the reason that only by means of them can any object whatsoever of experience be thought.

The transcendental deduction of all a priori concepts has thus a principle according to which the whole enquiry must be directed, namely, that they must be recognized as a priori conditions of the possibility of experience, whether of the intuition which is to be met with in it or of the thought. Concepts which yield the objective ground of the possibility of experience are for this very reason necessary. But the unfolding of the experience wherein they are encountered is not their deduction; it is only their illustration. For on any such [127] exposition they would be merely accidental. Save through their original relation to possible experience, in which all objects of knowledge are found, their relation to any one object would be quite incomprehensible.

{1}The illustrious Locke, failing to take account of these considerations, and meeting with pure concepts of the understanding in experience, deduced them also from experience, and yet proceeded so inconsequently that he attempted with their aid to obtain knowledge which far transcends all limits of experience. David Hume recognized that, in order to be able to do this, it was necessary that these concepts should have an a priori origin. But since he could not explain how it can be possible that the understanding must think concepts, which are not in themselves connected in the understanding, as being necessarily connected in the object, and since it never occurred to him that the understanding might itself, perhaps, through these concepts, be the author of the experience in which its objects are found, he was constrained to derive them from experience, namely, from a subjective necessity (that is, from custom), which arises from repeated association in experience, and which comes mistakenly to be regarded as objective. But from these premisses he argued quite consistently. It is impossible, he declared, with these concepts and the principles to which they give rise, to pass beyond the limits of experience. [128] Now this empirical derivation, in which both philosophers agree, cannot be reconciled with the scientific a priori knowledge which we do actually possess, namely, pure mathematics and general science of nature; and this fact therefore suffices to disprove such derivation.

While the former of these two illustrious men opened a wide door to enthusiasm -- for if reason once be allowed such rights, it will no longer allow itself to be kept within bounds by vaguely defined recommendations of moderation -- the other gave himself over entirely to skepticism, having, as he believed, discovered that what had hitherto been regarded as reason was but an all-prevalent illusion infecting our faculty of knowledge. We now propose to make trial whether it be not possible to find for human reason safe conduct between these two rocks, assigning to her determinate limits, and yet keeping open for her the whole field of her appropriate activities.

But first I shall introduce a word of explanation in regard to the categories. They are concepts of an object in general, by means of which the intuition of an object is regarded as determined in respect of one of the logical functions of judgment. Thus the function of the categorical judgment is that of the relation of subject to predicate; for example, 'All bodies are divisible'. But as regards the merely logical employment of the understanding, it remains undetermined to which of the two concepts the function of the subject, and to which the function of predicate, is to be assigned. For we can also say, 'Something divisible is a body'. But when the concept of body is brought under the category of substance, it is thereby determined that its empirical intuition in experience must always be considered as subject and never as mere predicate. Similarly with all the other categories.



[as in the 1st edition]
Section 2


THAT a concept, although itself neither contained in the concept of possible experience nor consisting of elements of a possible experience, should be produced completely a priori and should relate to an object, is altogether contradictory and impossible. For it would then have no content, since no intuition corresponds to it; and intuitions in general, through which objects can be given to us, constitute the field, the whole object, of possible experience. An a priori concept which did not relate to experience would be only the logical form of a concept, not the concept itself through which something is thought.

Pure a priori concepts, if such exist, cannot indeed contain anything empirical; yet, none the less, they can serve solely as a priori conditions of a possible experience. Upon this ground alone can their objective reality rest.

If, therefore, we seek to discover how pure concepts of understanding are possible, we must enquire what are the a priori conditions upon which the possibility of experience rests, and which remain as its underlying grounds when everything empirical is abstracted from appearances. A concept which universally and adequately expresses such a normal and [130] objective condition of experience would be entitled a pure concept of understanding. Certainly, once I am in possession of pure concepts of understanding, I can think objects which may be impossible, or which, though perhaps in themselves possible, cannot be given in any experience. For in the connecting of these concepts something may be omitted which yet necessarily belongs to the condition of a possible experience (as in the concept of a spirit). Or, it may be, pure concepts are extended further than experience can follow (as with the concept of God). But the elements of all modes of a priori knowledge, even of capricious and incongruous fictions, though they cannot, indeed, be derived from experience, since in that case they would not be knowledge a priori, must none the less always contain the pure a priori conditions of a possible experience and of an empirical object. Otherwise nothing would be thought through them, and they themselves, being without data, could never arise even in thought.

The concepts which thus contain a priori the pure thought involved in every experience, we find in the categories. If we can prove that by their means alone an object can be thought, this will be a sufficient deduction of them, and will justify their objective validity. But since in such a thought more than simply the faculty of thought, the understanding, is brought into play, and since this faculty itself, as a faculty of knowledge that is meant to relate to objects, calls for explanation in regard to the possibility of such relation, we must first of all consider, not in their empirical but in their transcendental constitution, the subjective sources which form the a priori foundation of the possibility of experience.

If each representation were completely foreign to every other, standing apart in isolation, no such thing as knowledge would ever arise. For knowledge is [essentially] a whole in which representations stand compared and connected. As sense contains a manifold in its intuition, I ascribe to it a synopsis. But to such synopsis a synthesis must always correspond; receptivity can make knowledge possible only when combined with spontaneity. Now this spontaneity is the ground of a threefold synthesis which must necessarily be found in all knowledge; namely, the apprehension of representations as modifications of the mind in intuition, their reproduction in [131] imagination, and their recognition in a concept. These point to three subjective sources of knowledge which make possible the understanding itself -- and consequently all experience as its empirical product.

Preliminary Remark

The deduction of the categories is a matter of such extreme difficulty, compelling us to penetrate so deeply into the first grounds of the possibility of our knowledge in general, that in order to avoid the elaborateness of a complete theory, and yet at the same time to omit nothing in so indispensable an enquiry, I have found it advisable in the four following passages rather to prepare than to instruct the reader. Systematic exposition of these elements of the understanding is first given in Section 3, immediately following. The reader must not therefore be deterred by obscurities in these earlier sections. They are unavoidable in an enterprise never before attempted. They will, as I trust, in the section referred to, finally give way to complete insight.

1. The Synthesis of Apprehension in Intuition

Whatever the origin of our representations, whether they are due to the influence of outer things, or are produced through inner causes, whether they arise a priori, or being appearances have an empirical origin, they must all, as modifications of the mind, belong to inner sense. All our knowledge is thus finally subject to time, the formal condition of inner sense. In it they must all be ordered, connected, and brought into relation. This is a general observation which, throughout what follows, must be borne in mind as being quite fundamental.

Every intuition contains in itself a manifold which can be represented as a manifold only in so far as the mind distinguishes the time in the sequence of one impression upon another; for each representation, in so far as it is contained in a single moment, can never be anything but absolute unity. In order that unity of intuition may arise out of this manifold (as is required in the representation of space) it must first be run through, and held together. This act I name the synthesis of apprehension, because it is directed immediately upon intuition, which does indeed offer a manifold, but a manifold which can [132] never be represented as a manifold, and as contained in a single representation, save in virtue of such a synthesis.

This synthesis of apprehension must also be exercised a priori, that is, in respect of representations which are not empirical. For without it we should never have a priori the representations either of space or of time. They can be produced only through the synthesis of the manifold which sensibility presents in its original receptivity. We have thus a pure synthesis of apprehension.

2. The Synthesis of Reproduction in Imagination

It is a merely empirical law, that representations which have often followed or accompanied one another finally become associated, and so are set in a relation whereby, even in the absence of the object, one of these representations can, in accordance with a fixed rule, bring about a transition of the mind to the other. But this law of reproduction presupposes that appearances are themselves actually subject to such a rule, and that in the manifold of these representations a coexistence or sequence takes place in conformity with certain rules. Otherwise our empirical imagination would never find opportunity for exercise appropriate to its powers, and so would remain concealed within the mind as a dead and to us unknown faculty. If cinnabar were sometimes red, sometimes black, sometimes light, sometimes heavy, if a man changed sometimes into this and sometimes into that animal form, if the country on the longest day were sometimes covered with fruit, sometimes with ice and snow, my empirical imagination would never find opportunity when representing red color to bring to mind heavy cinnabar. Nor could there be an empirical synthesis of reproduction, if a certain name were sometimes given to this, sometimes to that object, or were one and the same thing named sometimes in one way, sometimes in another, independently of any rule to which appearances are in themselves subject.

There must then be something which, as the a priori ground of a necessary synthetic unity of appearances, makes their reproduction possible. What that something is we [133] soon discover, when we reflect that appearances are not things in themselves, but are the mere play of our representations, and in the end reduce to determinations of inner sense. For if we can show that even our purest a priori intuitions yield no knowledge, save in so far as they contain a combination of the manifold such as renders a thoroughgoing synthesis of reproduction possible, then this synthesis of imagination is likewise grounded, antecedently to all experience, upon a priori principles; and we must assume a pure transcendental synthesis of imagination as conditioning the very possibility of all experience. For experience as such necessarily presupposes the reproducibility of appearances. When I seek to draw a line in thought, or to think of the time from one noon to another, or even to represent to myself some particular number, obviously the various manifold representations that are involved must be apprehended by me in thought one after the other. But if I were always to drop out of thought the preceding representations (the first parts of the line, the antecedent parts of the time period, or the units in the order represented), and did not reproduce them while advancing to those that follow, a complete representation would never be obtained: none of the above-mentioned thoughts, not even the purest and most elementary representations of space and time, could arise.

The synthesis of apprehension is thus inseparably bound up with the synthesis of reproduction. And as the former constitutes the transcendental ground of the possibility of all modes of knowledge whatsoever -- of those that are pure a priori no less than of those that are empirical -- the reproductive synthesis of the imagination is to be counted among the transcendental acts of the mind. We shall therefore entitle this faculty the transcendental faculty of imagination.

3. The Synthesis of Recognition in a Concept

If we were not conscious that what we think is the same as what we thought a moment before, all reproduction in the series of representations would be useless. For it would in its present state be a new representation which would not in any way belong to the act whereby it was to be gradually generated. [134] The manifold of the representation would never, therefore, form a whole, since it would lack that unity which only consciousness can impart to it. If, in counting, I forget that the units, which now hover before me, have been added to one another in succession, I should never know that a total is being produced through this successive addition of unit to unit, and so would remain ignorant of the number. For the concept of the number is nothing but the consciousness of this unity of synthesis.

The word 'concept' might of itself suggest this remark. For this unitary consciousness is what combines the manifold, successively intuited, and thereupon also reproduced, into one representation. This consciousness may often be only faint, so that we do not connect it with the act itself, that is, not in any direct manner with the generation of the representation, but only with the outcome [that which is thereby represented]. But notwithstanding these variations, such consciousness, however indistinct, must always be present; without it, concepts, and therewith knowledge of objects, are altogether impossible.

At this point we must make clear to ourselves what we mean by the expression 'an object of representations'. We have stated above that appearances are themselves nothing but sensible representations, which, as such and in themselves, must not be taken as objects capable of existing outside our power of representation. What, then, is to be understood when we speak of an object corresponding to, and consequently also distinct from, our knowledge? It is easily seen that this object must be thought only as something in general = x, since outside our knowledge we have nothing which we could set over against this knowledge as corresponding to it.

Now we find that our thought of the relation of all knowledge to its object carries with it an element of necessity; the object is viewed as that which prevents our modes of knowledge from being haphazard or arbitrary, and which determines them a priori in some definite fashion. For in so far as they are to relate to an object, they must necessarily agree [135] with one another, that is, must possess that unity which constitutes the concept of an object.

But it is clear that, since we have to deal only with the manifold of our representations, and since that x (the object) which corresponds to them is nothing to us -- being, as it is, something that has to be distinct from all our representations -- the unity which the object makes necessary can be nothing else than the formal unity of consciousness in the synthesis of the manifold of representations. It is only when we have thus produced synthetic unity in the manifold of intuition that we are in a position to say that we know the object. But this unity is impossible if the intuition cannot be generated in accordance with a rule by means of such a function of synthesis as makes the reproduction of the manifold a priori necessary, and renders possible a concept in which it is united. Thus we think a triangle as an object, in that we are conscious of the combination of three straight lines according to a rule by which such an intuition can always be represented. This unity of rule determines all the manifold, and limits it to conditions which make unity of apperception possible. The concept of this unity is the representation of the object = x, which I think through the predicates, above mentioned, of a triangle.

All knowledge demands a concept, though that concept may, indeed, be quite imperfect or obscure. But a concept is always, as regards its form, something universal which serves as a rule. The concept of body, for instance, as the unity of the manifold which is thought through it, serves as a rule in our knowledge of outer appearances. But it can be a rule for intuitions only in so far as it represents in any given appearances the necessary reproduction of their manifold, and thereby the synthetic unity in our consciousness of them. The concept of body, in the perception of something outside us, necessitates the representation of extension, and therewith representations of impenetrability, shape, etc.

All necessity, without exception, is grounded in a transcendental condition. There must, therefore, be a transcendental ground of the unity of consciousness in the synthesis of the manifold of all our intuitions, and consequently also of the concepts of objects in general, and so of all objects of experience, a ground without which it would be impossible [136] to think any object for our intuitions; for this object is no more than that something, the concept of which expresses such a necessity of synthesis.

This original and transcendental condition is no other than transcendental apperception. Consciousness of self according to the determinations of our state in inner perception is merely empirical, and always changing. No fixed and abiding self can present itself in this flux of inner appearances. Such consciousness is usually named inner sense, or empirical apperception. What has necessarily to be represented as numerically identical cannot be thought as such through empirical data. To render such a transcendental presupposition valid, there must be a condition which precedes all experience, and which makes experience itself possible.

There can be in us no modes of knowledge, no connection or unity of one mode of knowledge with another, without that unity of consciousness which precedes all data of intuitions, and by relation to which representation of objects is alone possible. This pure original unchangeable consciousness I shall name transcendental apperception. That it deserves this name is clear from the fact that even the purest objective unity, namely, that of the a priori concepts (space and time), is only possible through relation of the intuitions to such unity of consciousness. The numerical unity of this apperception is thus the a priori ground of all concepts, just as the manifoldness of space and time is the a priori ground of the intuitions of sensibility.

This transcendental unity of apperception forms out of all possible appearances, which can stand alongside one another in one experience, a connection of all these representations according to laws. For this unity of consciousness would be impossible if the mind in knowledge of the manifold could not become conscious of the identity of function whereby it synthetically combines it in one knowledge. The original and necessary consciousness of the identity of the self is thus at the same time a consciousness of an equally necessary unity of the synthesis of all appearances according to concepts, that [137] is, according to rules, which not only make them necessarily reproducible but also in so doing determine an object for their intuition, that is, the concept of something wherein they are necessarily interconnected. For the mind could never think its identity in the manifoldness of its representations, and indeed think this identity a priori, if it did not have before its eyes the identity of its act, whereby it subordinates all synthesis of apprehension (which is empirical) to a transcendental unity, thereby rendering possible their interconnection according to a priori rules.

Now, also, we are in a position to determine more adequately our concept of an object in general. All representations have, as representations, their object, and can themselves in turn become objects of other representations. Appearances are the sole objects which can be given to us immediately, and that in them which relates immediately to the object is called intuition. But these appearances are not things in themselves; they are only representations, which in turn have their object -- an object which cannot itself be intuited by us, and which may, therefore, be named the non-empirical, that is, transcendental object = x.

The pure concept of this transcendental object, which in reality throughout all our knowledge is always one and the same, is what can alone confer upon all our empirical concepts in general relation to an object, that is, objective reality. This concept cannot contain any determinate intuition, and therefore refers only to that unity which must be met with in any manifold of knowledge which stands in relation to an object. This relation is nothing but the necessary unity of consciousness, and therefore also of the synthesis of the manifold, through a common function of the mind, which combines it in one representation. Since this unity must be regarded as necessary a priori -- otherwise knowledge would be without an object -- the relation to a transcendental object, that is, the objective reality of our empirical knowledge, rests on the transcendental law, that all appearances, in so far as through them objects are to be given to us, must stand under those a priori rules of synthetical unity whereby the interrelating [138] of these appearances in empirical intuition is alone possible. In other words, appearances in experience must stand under the conditions of the necessary unity of apperception, just as in mere intuition they must be subject to the formal conditions of space and of time. Only thus can any knowledge become possible at all.

4. Preliminary Explanation of the Possibility of the Categories, as Knowledge a priori

There is one single experience in which all perceptions are represented as in thoroughgoing and orderly connection, just as there is only one space and one time in which all modes of appearance and all relation of being or not being occur. When we speak of different experiences, we can refer only to the various perceptions, all of which, as such, belong to one and the same general experience. This thoroughgoing synthetic unity of perceptions is indeed the form of experience; it is nothing else than the synthetic unity of appearances in accordance with concepts.

Unity of synthesis according to empirical concepts would be altogether accidental, if these latter were not based on a transcendental ground of unity. Otherwise it would be possible for appearances to crowd in upon the soul, and yet to be such as would never allow of experience. Since connection in accordance with universal and necessary laws would be lacking, all relation of knowledge to objects would fall away. The appearances might, indeed, constitute intuition without thought, but not knowledge; and consequently would be for us as good as nothing.

The a priori conditions of a possible experience in general are at the same time conditions of the possibility of objects of experience. Now I maintain that the categories, above cited, are nothing but the conditions of thought in a possible experience, just as space and time are the conditions of intuition for that same experience. They are fundamental concepts by which we think objects in general for appearances, and have therefore a priori objective validity. This is exactly what we desired to prove. [139]

But the possibility, indeed the necessity, of these categories rests on the relation in which our entire sensibility, and with it all possible appearances, stand to original apperception. In original apperception everything must necessarily conform to the conditions of the thoroughgoing unity of self-consciousness, that is, to the universal functions of synthesis, namely, of that synthesis according to concepts in which alone apperception can demonstrate a priori its complete and necessary identity. Thus the concept of a cause is nothing but a synthesis (of that which follows in the time-series, with other appearances) according to concepts; and without such unity, which has its a priori rule, and which subjects the appearances to itself, no thoroughgoing, universal, and therefore necessary, unity of consciousness would be met with in the manifold of perceptions. These perceptions would not then belong to any experience, consequently would be without an object, merely a blind play of representations, less even than a dream.

All attempts to derive these pure concepts of understanding from experience, and so to ascribe to them a merely empirical origin, are entirely vain and useless. I need not insist upon the fact that, for instance, the concept of a cause involves the character of necessity, which no experience can yield. Experience does indeed show that one appearance customarily follows upon another, but not that this sequence is necessary, nor that we can argue a priori and with complete universality from the antecedent, viewed as a condition, to the consequent. But as regards the empirical rule of association, which we must postulate throughout when we assert that everything in the series of events is so subject to rule that nothing ever happens save in so far as something precedes it on which it universally follows -- upon what I ask, does this rule, as a law of nature, rest? How is this association itself possible? The ground of the possibility of the association of the manifold, so far as it lies in the object, is named the affinity of the manifold. I therefore ask, how are we to make comprehensible to ourselves the thoroughgoing affinity of appearances, whereby they stand and must stand under unchanging laws?

On my principles it is easily explicable. All possible appearances, as representations, belong to the totality of a possible [140] self-consciousness. But as self-consciousness is a transcendental representation, numerical identity is inseparable from it, and is a priori certain. For nothing can come to our knowledge save in terms of this original apperception. Now, since this identity must necessarily enter into the synthesis of all the manifold of appearances, so far as the synthesis is to yield empirical knowledge, the appearances are subject to a priori conditions, with which the synthesis of their apprehension must be in complete accordance. The representation of a universal condition according to which a certain manifold can be posited in uniform fashion is called a rule, and, when it must be so posited, a law. Thus all appearances stand in thoroughgoing connection according to necessary laws, and therefore in a transcendental affinity, of which the empirical is a mere consequence.

That nature should direct itself according to our subjective ground of apperception, and should indeed depend upon it in respect of its conformity to law, sounds very strange and absurd. But when we consider that this nature is not a thing in itself but is merely an aggregate of appearances, so many representations of the mind, we shall not be surprised that we can discover it only in the radical faculty of all our knowledge, namely, in transcendental apperception, in that unity on account of which alone it can be entitled object of all possible experience, that is, nature. Nor shall we be surprised that just for this very reason this unity can be known a priori, and therefore as necessary. Were the unity given in itself independently of the first sources of our thought, this would never be possible. We should not then know of any source from which we could obtain the synthetic propositions asserting such a universal unity of nature. For they would then have to be derived from the objects of nature themselves; and as this could take place only empirically, none but a merely accidental unity could be obtained, which would fall far short of the necessary interconnection that we have in mind when we speak of nature.



Section 3


What we have expounded separately and singly in the preceding section, we shall now present in systematic interconnection. There are three subjective sources of knowledge upon which rests the possibility of experience in general and of knowledge of its objects -- sense, imagination, and apperception. Each of these can be viewed as empirical, namely, in its application to given appearances. But all of them are likewise a priori elements or foundations, which make this empirical employment itself possible. Sense represents appearances empirically in perception, imagination in association (and reproduction), apperception in the empirical consciousness of the identity of the reproduced representations with the appearances whereby they were given, that is, in recognition.

But all perceptions are grounded a priori in pure intuition (in time, the form of their inner intuition as representations), association in pure synthesis of imagination, and empirical consciousness in pure apperception, that is, in the thoroughgoing identity of the self in all possible representations.

If, now, we desire to follow up the inner ground of this connection of the representations to the point upon which they have all to converge in order that they may therein for the first time acquire the unity of knowledge necessary for a possible experience, we must begin with pure apperception. Intuitions are nothing to us, and do not in the least concern us if they cannot be taken up into consciousness, in which they may participate either directly or indirectly. In this way alone is any knowledge possible. We are conscious a priori of the complete identity of the self in respect of all representations which can even belong to our knowledge, as being a necessary condition of the possibility of all representations. [142] For in me they can represent something only in so far as they belong with all others to one consciousness, and therefore must be at least capable of being so connected. This principle holds a priori, and may be called the transcendental principle of the unity of all that is manifold in our representations, and consequently also in intuition. Since this unity of the manifold in one subject is synthetic, pure apperception supplies a principle of the synthetic unity of the manifold in all possible intuition.{2}

This synthetic unity presupposes or includes a synthesis, and if the former is to be a priori necessary, the synthesis must also be a priori. The transcendental unity of apperception thus relates to the pure synthesis of imagination, as an a priori condition of the possibility of all combination of the manifold in one knowledge. But only the productive synthesis of the [143] imagination can take place a priori; the reproductive rests upon empirical conditions. Thus the principle of the necessary unity of pure (productive) synthesis of imagination, prior to apperception, is the ground of the possibility of all knowledge, especially of experience.

We entitle the synthesis of the manifold in imagination transcendental, if without distinction of intuitions it is directed exclusively to the a priori combination of the manifold; and the unity of this synthesis is called transcendental, if it is represented as a priori necessary in relation to the original unity of apperception. Since this unity of apperception underlies the possibility of all knowledge, the transcendental unity of the synthesis of imagination is the pure form of all possible knowledge; and by means of it all objects of possible experience must be represented a priori.

The unity of apperception in relation to the synthesis of imagination is the understanding; and this same unity, with reference to the transcendental synthesis of the imagination, the pure understanding. In the understanding there are then pure a priori modes of knowledge which contain the necessary unity of the pure synthesis of imagination in respect of all possible appearances. These are the categories, that is, the pure concepts of understanding. The empirical faculty of knowledge in man must therefore contain an understanding which relates to all objects of the senses, although only by means of intuition and of its synthesis through imagination. All appearances, as data for a possible experience, are subject to this understanding. This relation of appearances to possible experience is indeed necessary, for otherwise they would yield no knowledge and would not in any way concern us. We have, therefore, to recognize that pure understanding, by means of the categories, is a formal and synthetic principle of all experiences, and that appearances have a necessary relation to the understanding.

We will now, starting from below, namely, with the empirical, strive to make clear the necessary connection in which understanding, by means of the categories, stands to appearances. What is first given to us is appearance. When combined with consciousness, it is called perception. (Save through its [144] relation to a consciousness that is at least possible, appearance could never be for us an object of knowledge, and so would be nothing to us; and since it has in itself no objective reality, but exists only in being known, it would be nothing at all. ) Now, since every appearance contains a manifold, and since different perceptions therefore occur in the mind separately and singly, a combination of them, such as they cannot have in sense itself, is demanded. There must therefore exist in us an active faculty for the synthesis of this manifold. To this faculty I give the title, imagination. Its action, when immediately directed upon perceptions, I entitle apprehension.{3} Since imagination has to bring the manifold of intuition into the form of an image, it must previously have taken the impressions up into its activity, that is, have apprehended them.

But it is clear that even this apprehension of the manifold would not by itself produce an image and a connection of the impressions, were it not that there exists a subjective ground which leads the mind to reinstate a preceding perception alongside the subsequent perception to which it has passed, and so to form whole series of perceptions. This is the reproductive faculty of imagination, which is merely empirical.

If, however, representations reproduced one another in any order, just as they happened to come together, this would not lead to any determinate connection of them, but only to accidental collocations; and so would not give rise to any knowledge. Their reproduction must, therefore, conform to a rule, in accordance with which a representation connects in the imagination with some one representation in preference to another. This subjective and empirical ground of reproduction according to rules is what is called the association of representations.

Now if this unity of association had not also an objective [145] ground which makes it impossible that appearances should be apprehended by the imagination otherwise than under the condition of a possible synthetic unity of this apprehension, it would be entirely accidental that appearances should fit into a connected whole of human knowledge. For even though we should have the power of associating perceptions, it would remain entirely undetermined and accidental whether they would themselves be associable; and should they not be associable, there might exist a multitude of perceptions, and indeed an entire sensibility, in which much empirical consciousness would arise in my mind, but in a state of separation, and without belonging to a consciousness of myself. This, however, is impossible. For it is only because I ascribe all perceptions to one consciousness (original apperception) that I can say of all perceptions that I am conscious of them. There must, therefore, be an objective ground (that is, one that can be comprehended a priori, antecedently to all empirical laws of the imagination) upon which rests the possibility, nay, the necessity, of a law that extends to all appearances -- a ground, namely, which constrains us to regard all appearances as data of the senses that must be associable in themselves and subject to universal rules of a thoroughgoing connection in their reproduction. This objective ground of all association of appearances I entitle their affinity. It is nowhere to be found save in the principle of the unity of apperception, in respect of all knowledge which is to belong to me. According to this principle all appearances, without exception, must so enter the mind or be apprehended, that they conform to the unity of apperception. Without synthetic unity in their connection, this would be impossible; and such synthetic unity is itself, therefore, objectively necessary.

The objective unity of all empirical consciousness in one consciousness, that of original apperception, is thus the necessary condition of all possible perception; and [this being recognized we can prove that] the affinity of all appearances, near or remote, is a necessary consequence of a synthesis in imagination which is grounded a priori on rules.

Since the imagination is itself a faculty of a priori synthesis, we assign to it the title, productive imagination. In so far as it aims at nothing but necessary unity in the synthesis of [146] what is manifold in appearance, it may be entitled the transcendental function of imagination. That the affinity of appearances, and with it their association, and through this, in turn, their reproduction according to laws, and so [as involving these various factors] experience itself, should only be possible by means of this transcendental function of imagination, is indeed strange, but is none the less an obvious consequence of the preceding argument. For without this transcendental function no concepts would together make up a unitary experience.

The abiding and unchanging 'I' (pure apperception) forms the correlate of all our representations in so far as it is to be at all possible that we should become conscious of them. All consciousness as truly belongs to an all-comprehensive pure apperception, as all sensible intuition, as representation, does to a pure inner intuition, namely, to time. It is this apperception which must be added to pure imagination, in order to render its function intellectual. For since the synthesis of imagination connects the manifold only as it appears in intuition, as, for instance, in the shape of a triangle, it is, though exercised a priori, always in itself sensible. And while concepts, which belong to the understanding, are brought into play through relation of the manifold to the unity of apperception, it is only by means of the imagination that they can be brought into relation to sensible intuition.

A pure imagination, which conditions all a priori knowledge, is thus one of the fundamental faculties of the human soul. By its means we bring the manifold of intuition on the one side, into connection with the condition of the necessary unity of pure apperception on the other. The two extremes, namely sensibility and understanding, must stand in necessary connection with each other through the mediation of this transcendental function of imagination, because otherwise the former, though indeed yielding appearances, would supply no objects of empirical knowledge, and consequently no experience. Actual experience, which is constituted by apprehension, association (reproduction), and finally recognition of appearances, contains in recognition, the last and highest of these [147] merely empirical elements of experience, certain concepts which render possible the formal unity of experience, and therewith all objective validity (truth) of empirical knowledge. These grounds of the recognition of the manifold, so far as they concern solely the form of an experience in general, are the categories. Upon them is based not only all formal unity in the [transcendental] synthesis of imagination, but also, thanks to that synthesis, all its empirical employment (in recognition, reproduction, association, apprehension) in connection with the appearances. For only by means of these fundamental concepts can appearances belong to knowledge or even to our consciousness, and so to ourselves.

Thus the order and regularity in the appearances, which we entitle nature, we ourselves introduce. We could never find them in appearances, had no we ourselves, or the nature of our mind, originally set them there. For this unity of nature has to be a necessary one, that is, has to be an a priori certain unity of the connection of appearances; and such synthetic unity could not be established a priori if there were not subjective grounds of such unity contained a priori in the original cognitive powers of our mind, and if these subjective conditions, inasmuch as they are the grounds of the possibility of knowing any object whatsoever in experience, were not at the same time objectively valid.

We have already defined the understanding in various different ways: as a spontaneity of knowledge (in distinction from the receptivity of sensibility), as a power of thought, as a faculty of concepts, or again of judgments. All these definitions, when they are adequately understood, are identical. We may now characterize it as the faculty of rules. This distinguishing mark is more fruitful, and approximates more closely to its essential nature. Sensibility gives us forms (of intuition), but understanding gives us rules. The latter is always occupied in investigating appearances, in order to detect some rule in them. Rules, so far as they are objective, and therefore necessarily depend upon the knowledge of the object, are called laws. Although we learn many laws through [148] experience, they are only special determinations of still higher laws, and the highest of these, under which the others all stand, issue a priori from the understanding itself. They are not borrowed from experience; on the contrary, they have to confer upon appearances their conformity to law, and so to make experience possible. Thus the understanding is something more than a power of formulating rules through comparison of appearances; it is itself the lawgiver of nature. Save through it, nature, that is, synthetic unity of the manifold of appearances according to rules, would not exist at all (for appearances, as such, cannot exist outside us -- they exist only in our sensibility); and this nature, as object of knowledge in an experience, with everything which it may contain, is only possible in the unity of apperception. The unity of apperception is thus the transcendental ground of the necessary conformity to law of all appearances in one experience. This same unity of apperception in respect to a manifold of representations (determining it out of a unity) acts as the rule, and the faculty of these rules is the understanding. All appearances, as possible experiences, thus lie a priori in the understanding, and receive from it their formal possibility, just as, in so far as they are mere intuitions, they lie in the sensibility, and are, as regards their form, only possible through it.

However exaggerated and absurd it may sound, to say that the understanding is itself the source of the laws of nature, and so of its formal unity, such an assertion is none the less correct, and is in keeping with the object to which it refers, namely, experience. Certainly, empirical laws, as such, can never derive their origin from pure understanding. That is as little possible as to understand completely the inexhaustible multiplicity of appearances merely by reference to the pure form of sensible intuition. But all empirical laws are only special determinations of the pure laws of understanding, under which, and according to the norm of which, they first become possible. Through them appearances take on an orderly character, just as these same appearances, despite [149] the differences of their empirical form, must none the less always be in harmony with the pure form of sensibility.

Pure understanding is thus in the categories the law of the synthetic unity of all appearances, and thereby first and originally makes experience, as regards its form, possible. This is all that we were called upon to establish in the transcendental deduction of the categories, namely, to render comprehensible this relation of understanding to sensibility, and, by means of sensibility, to all objects of experience. The objective validity of the pure a priori concepts is thereby made intelligible, and their origin and truth determined.

Summary Representation of the Correctness of this Deduction of the Pure Concepts of Understanding, and of its being the only Deduction possible

If the objects with which our knowledge has to deal were things in themselves, we could have no a priori concepts of them. For from what source could we obtain the concepts? If we derived them from the object (leaving aside the question how the object could become known to us), our concepts would be merely empirical, not a priori. And if we derived them from the self, that which is merely in us could not determine the character of an object distinct from our representations, that is, could not be a ground why a thing should exist characterized by that which we have in our thought, and why such a representation should not, rather, be altogether empty. But if, on the other hand, we have to deal only with appearances, it is not merely possible, but necessary, that certain a priori concepts should precede empirical knowledge of objects. For since a mere modification of our sensibility can never be met with outside us, the objects, as appearances, constitute an object which is merely in us. Now to assert in this manner, that all these appearances, and consequently all objects with which we can occupy ourselves, are one and all in me, that is, are determinations of my identical self, is only another way of saying that there must be a complete unity of them in one and the same apperception. But this unity of possible consciousness also constitutes the form of all knowledge of objects; through it the manifold is thought as belonging to a [150] single object. Thus the mode in which the manifold of sensible representation (intuition) belongs to one consciousness precedes all knowledge of the object as the intellectual form of such knowledge, and itself constitutes a formal a priori knowledge of all objects, so far as they are thought (categories). The synthesis of the manifold through pure imagination, the unity of all representations in relation to original apperception, precede all empirical knowledge. Pure concepts of understanding are thus a priori possible, and, in relation to experience, are indeed necessary; and this for the reason that our knowledge has to deal solely with appearances, the possibility of which lies in ourselves, and the connection and unity of which (in the representation of an object) are to be met with only in ourselves. Such connection and unity must therefore precede all experience, and are required for the very possibility of it in its formal aspect. From this point of view, the only feasible one, our deduction of the categories has been developed.

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{1} There are three original sources (capacities or faculties of the soul) which contain the conditions of the possibility of all experience, and cannot themselves be derived from any other faculty of the mind, namely, sense, imagination, and apperception. Upon them are grounded (1) the synopsis of the manifold a priori through sense; (2) the synthesis of this manifold through imagination; finally (3) the unity of this synthesis through original apperception. All these faculties have a transcendental (as well as an empirical) employment which concerns the form alone, and is possible a priori. As regards sense, we have treated of this above in the first part; we shall now endeavour to comprehend the nature of the other two. [Back]

{2} This proposition is of great importance and calls for careful consideration. All representations have a necessary relation to a possible empirical consciousness. For if they did not have this, and if it were altogether impossible to become conscious of them, this would practically amount to the admission of their non-existence. But all empirical consciousness has a necessary relation to a transcendental consciousness which precedes all special experience, namely, the consciousness of myself as original apperception. It is therefore absolutely necessary that in my knowledge all consciousness should belong to a single consciousness, that of myself. Here, then, is a synthetic unity of the manifold (of consciousness), which is known a priori, and so yields the ground for synthetic a priori propositions which concern pure thought, just as do space and time for the propositions which refer to the form of pure intuition. The synthetic proposition, that all the variety of empirical consciousness must be combined in one single self-consciousness, is the absolutely first and synthetic principle of our thought in general. But it must not be forgotten that the bare representation 'I' in relation to all other representations (the collective unity of which it makes possible) is transcendental consciousness. Whether this representation is clear (empirical consciousness) or obscure, or even whether it ever actually occurs, does not here concern us. But the possibility of the logical form of all knowledge is necessarily conditioned by relation to this apperception as a faculty. [Back]

{3} Psychologists have hitherto failed to realize that imagination is a necessary ingredient of perception itself. This is due partly to the fact that that faculty has been limited to reproduction, partly to the belief that the senses not only supply impressions but also combine them so as to generate images of objects. For that purpose something more than the mere receptivity of impressions is undoubtedly required, namely, a function for the synthesis of them. [Back]

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