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in whatever manner and by whatever means a mode of knowledge 82 may relate to objects, intuition is that through which it is in immediate relation to them, and from which all thought gains its material. But intuition takes place only in so far as the object is given to us. This again is only possible, to man at least, 83 in so far as the mind is affected in a certain way. The capacity (receptivity) for receiving representations through the mode in which we are affected by objects, is entitled sensibility . Objects are given to us by means of sensibility, and it alone yields us intuitions ; they are thought through the understanding, and from the understanding arise concepts . But all thought must, directly or indirectly, by way of certain characters, 84 relate ultimately to intuitions, and therefore, with us, to sensibility, because in no other way can an object be given to us.
The effect of an object upon the faculty of representation, so far as we are affected by it, is sensation . That intuition which is in relation to the object through sensation, is entitled empirical . The undetermined object of an empirical intuition is entitled appearance .
That in the appearance which corresponds to sensation I term its matter ; but that which so determines 85 the manifold of appearance that it allows of being ordered 86 in certain relations, I term the form of appearance. That in which alone the sensations can be posited and ordered in a certain form, cannot itself be sensation; and therefore, while the matter of all appearance is given to us a posteriori only, its form must lie ready for the sensations a priori in the mind, and so must allow of being considered apart from all sensation.
I term all representations pure (in the transcendental sense) in which there is nothing that belongs to sensation. The pure form of sensible intuitions in general, in which all the manifold of intuition is intuited in certain relations, must be found in the mind a priori . This pure form of sensibility may also itself be called pure intuition . If, then, I take away from the representation of a body that which the understanding thinks in regard to it, substance, force, divisibility, etc., and likewise what belongs to sensation, impenetrability, hardness, colour, etc., something still remains over from this empirical intuition, namely, extension and figure. These belong to pure intuition, which, even without any actual object of the senses or of sensation, exists in the mind a priori as a mere form of sensibility.
The science of all principles of a priori sensibility I call transcendental aesthetic . 87 There must be such a science, forming the first part of the transcendental doctrine of elements, in distinction from that part which deals with the principles of pure thought, and which is called transcendental logic.
In the transcendental aesthetic we shall, therefore, first isolate sensibility , by taking away from it everything which the understanding thinks through its concepts, so that nothing may be left save empirical intuition. Secondly, we shall also separate off from it everything which belongs to sensation, so that nothing may remain save pure intuition and the mere form of appearances, which is all that sensibility can supply a priori . In the course of this investigation it will be found that there are two pure forms of sensible intuition, serving as principles of a priori knowledge, namely, space and time. To the consideration of these we shall now proceed.
By means of outer sense, a property of our mind, we represent to ourselves objects as outside us, and all without exception in space. In space their shape, magnitude, and relation to one another are determined or determinable. Inner sense, by means of which the mind intuits itself or its inner state, yields indeed no intuition of the soul itself as an object; but there is nevertheless a determinate form [namely, time] in which alone the intuition of inner states is possible, and everything which belongs to inner determinations is therefore represented in relations of time. Time cannot be outwardly intuited, any more than space can be intuited as something in us. What, then, are space and time? Are they real existences? Are they only determinations or relations of things, yet such as would belong to things even if they were not intuited? Or are space and time such that they belong only to the form of intuition, and therefore to the subjective constitution of our mind, apart from which they could not be ascribed to anything whatsoever? In order to obtain light upon these questions, let us first give an exposition of the concept of space. 89 By exposition 90 ( expositio ) I mean the clear, though not necessarily exhaustive, representation of that which belongs to a concept: the exposition is metaphysical when it contains that which exhibits the concept as given a priori .
1. Space is not an empirical concept which has been derived from outer experiences. For in order that certain sensations be referred to something outside me (that is, to something in another region of space from that in which I find myself), and similarly in order that I may be able to represent them as outside and alongside 91 one another, and accordingly as not only different but as in different places, the representation of space must be presupposed. The representation of space cannot, therefore, be empirically obtained from the relations of outer appearance. On the contrary, this outer experience is itself possible at all only through that representation.
2. Space is a necessary a priori representation, which underlies all outer intuitions. We can never represent to ourselves the absence of space, though we can quite well think it as empty of objects. It must therefore be regarded as the condition of the possibility of appearances, and not as a determination dependent upon them. It is an a priori representation, which necessarily underlies outer appearances. 92
3. 93 Space is not a discursive or, as we say, general concept of relations of things in general, but a pure intuition. For, in the first place, we can represent to ourselves only one space; and if we speak of diverse spaces, we mean thereby only parts of one and the same unique space. Secondly, these parts cannot precede the one all-embracing space, as being, as it were, constituents out of which it can be composed; on the contrary, they can be thought only as in it. Space is essentially one; the manifold in it, and therefore the general concept of spaces, depends solely on [the introduction of] limitations. Hence it follows that an a priori , and not an empirical, intuition underlies all concepts of space. For kindred reasons, geometrical propositions, that, for instance, in a triangle two sides together are greater than the third, can never be derived from the general concepts of line and triangle, but only from intuition, and this indeed a priori , with apodeictic certainty.
4. 94 Space is represented as an infinite given magnitude. Now every concept must be thought as a representation which is contained in an infinite number of different possible representations (as their common character), and which therefore contains these under itself; but no concept, as such, can be thought as containing an infinite numbfer of representations within itself. It is in this latter way, however, that space is thought; for all the parts of space coexist ad in f initum . Consequently, the original representation of space is an a priori intuition, not a concept.
I understand by a transcendental exposition the explanation of a concept, as a principle from which the possibility of other a priori synthetic knowledge can be understood. For this purpose it is required (1) that such knowledge does really flow from the given concept, (2) that this knowledge is possible only on the assumption of a given mode of explaining the concept.
Geometry is a science which determines the properties of space synthetically, and yet a priori . What, then, must be our representation of space, in order that such knowledge of it may be possible? It must in its origin be intuition; for from a mere concept no propositions can be obtained which go beyond the concept—as happens in geometry (Introduction, V). 96 Further, this intuition must be a priori , that is, it must be found in us prior to any perception of an object, and must therefore be pure, not empirical, intuition. For geometrical propositions are one and all apodeictic, that is, are bound up with the consciousness of their necessity; for instance, that space has only three dimensions. Such propositions cannot be empirical or, in other words, judgments of experience, nor can they be derived from any such judgments (Introduction, II). 97
How, then, can there exist in the mind an outer intuition which precedes the objects themselves, and in which the concept of these objects can be determined a priori ? Manifestly, not otherwise than in so far as the intuition has its seat in the subject only, as the formal character of the subject, in virtue of which, in being affected by objects, it obtains immediate representation , that is, intuition , of them; and only in so far, therefore, as it is merely the form of outer sense in general.
Our explanation is thus the only explanation that makes intelligible the possibility of geometry, as a body of a priori synthetic knowledge. Any mode of explanation which fails to do this, although it may otherwise seem to be somewhat similar, can by this criterion 98 be distinguished from it with the greatest certainty.
( a ) Space does not represent any property of things in themselves, nor does it represent them in their relation to one another. That is to say, space does not represent any determination that attaches to the objects themselves, and which remains even when abstraction has been made of all the subjective conditions of intuition. For no determinations, whether absolute or relative, can be intuited prior to the existence of the things to which they belong, and none, therefore, can be intuited a priori .
( b ) Space is nothing but the form of all appearances of outer sense. It is the subjective condition of sensibility, under which alone outer intuition is possible for us. Since, then, the receptivity of the subject, its capacity to be affected by objects, must necessarily precede all intuitions of these objects, it can readily be understood how the form of all appearances can be given prior to all actual perceptions, and so exist in the mind a priori , and how, as a pure intuition, in which all objects must be determined, it can contain, prior to all experience, principles which determine the relations of these objects.
It is, therefore, solely from the human standpoint that we can speak of space, of extended things, etc. If we depart from the subjective condition under which alone we can have outer intuition, namely, liability to be affected by objects, the representation of space stands for nothing whatsoever. This predicate can be ascribed to things only in so far as they appear to us, that is, only to objects of sensibility. The constant form of this receptivity, which we term ‘sensibility, is a necessary condition of all the relations in which objects can be intuited as outside us; and if wef abstract from these objects, it is a pure intuition, and bears the name of space. Since we cannot treat the special conditions of sensibility as conditions of the possibility of things, but only of their appearances, we can indeed say that space comprehends all things that appear to us as external, but not all things in themselves, by whatever subject they are intuited, or whether they be intuited or not. For we cannot judge in regard to the intuitions of other thinking beings, whether they are bound by the same conditions as those which limit our intuition and which for us are universally valid. If we add to the concept of the subject of a judgment the limitation under which the judgment is made, the judgment is then unconditionally valid. The proposition, that all things are side by side in space, is valid under 99 the limitation that these things are viewed as objects of our sensible intuition. If, now, I add the condition to the concept, and say that all things, as outer appearances, are side by side in space, the rule is valid universally and without limitation. Our exposition 100 therefore establishes the reality , that is, the objective validity, of space in respect of whatever can be presented to us outwardly as object, but also at the same time the ideality of space in respect of things when they are considered in themselves through reason, that is, without regard to the constitution of our sensibility. We assert, then, the empirical reality of space, as regards all possible outer experience; and yet at the same time we assert its transcendental ideality —in other words, that it is nothing at all, immediately we withdraw the above condition, namely, its limitation to possible experience, and so look upon it as something that underlies things in themselves.
With the sole exception of space there is no subjective representation, referring to something outer , which could be entitled [at once] objective [and] a priori . For 101 there is no other subjective representation from which we can derive a priori synthetic propositions, as we can from intuition in space (§ 3 102 ). Strictly speaking, therefore, these other representations have no ideality, although they agree with the representation of space in this respect, that they belong merely to the subjective constitution of our manner of sensibility, for instance, of sight, hearing, touch, 103 as in the case of the sensations of colours, sounds, and heat, which, since they are mere sensations and not intuitions, do not of themselves yield knowledge of any object, least of all any a priori knowledge.
The above remark is intended only to guard anyone from supposing that the ideality of space as here asserted can be illustrated by examples so altogether insufficient as colours, taste, etc. For these cannot rightly be regarded as properties of things, but only as changes in the subject, changes which may, indeed, be different for different men. In such examples as these, that which originally is itself only appearance, for instance, a rose, is being treated by the empirical understanding as a thing in itself, which, nevertheless, in respect of its colour can appear differently to every observer. The transcendental concept of appearances in space, on the other hand, is a critical reminder that nothing intuited in space is a thing in itself, that space is not a form inhering in things in themselves as their intrinsic property, that objects in themselves are quite unknown to us, and that what we call outer objects are nothing but mere representations of our sensibility, the form of which is space. The true correlate of sensibility, the thing in itself, is not known, and cannot be known, through these representations; and in experience no question is ever asked in regard to it.
1. Time is not an empirical concept that has been derived from any experience. For neither coexistence nor succession would ever come within our perception, if the representation of time were not presupposed as underlying them a priori . Only on the presupposition of time can we represent to ourselves a number of things as existing at one and the same time (simultaneously) or at different times (successively).
2. Time is a necessary representation that underlies all intuitions. We cannot, in respect of appearances in general, remove time itself, though we can quite well think time as void of appearances.Time is, therefore, given a priori . In it alone is actuality of appearances possible at all. Appearances may, one and all, vanish; “but time (as the universal condition of their possibility) 105 cannot itself be removed.
3. The possibility of apodeictic principles concerning the relations of time, or of axioms of time in general, is also grounded upon this a priori necessity. Time has only one dimension; different times are not simultaneous but successive (just as different spaces are not successive but simultaneous). These principles cannot be derived from experience, for experience would give neither strict universality nor apodeictic certainty. We should only be able to say that common experience teaches us that it is so; not that it must be so. These principles are valid as rules under which alone experiences are possible; and they instruct us in regard to 106 the experiences, not by means of them.
4. Time is not a discursive, or what is called a general concept, but a pure form of sensible intuition. Different times are but parts of one and the same time; and the representation which can be given only through a single object is intuition. Moreover, the proposition that different times cannot be simultaneous is not to be derived from a general concept. The proposition is synthetic, and cannot have its origin in concepts alone. It is immediately contained in the intuition and representation of time.
5. The infinitude of time signifies nothing more than that every determinate magnitude of time is possible only through limitations of one single time that underlies it. The original representation, time , must therefore be given as unlimited. But when an object is so given that its parts, and every quantity of it, can be determinately represented only through limitation, the whole representation cannot be given through concepts, since they contain only partial representations; 107 on the contrary, such concepts must themselves rest on immediate intuition.
I may here refer to No. 3, 109 where, for the sake of brevity, I have placed under the title of metaphysical exposition what is properly transcendental. Here I may add that the concept of alteration, 110 and with it the concept of motion, as alteration of place, is possible only through and in the representation of time; and that if this representation were not an a priori (inner) intuition, no concept, no matter what it might be, could render comprehensible the possibility of an alteration, that is, of a combination of contradictorily opposed predicates in one and the same object, for instance, the being and the not-being of one and the same thing in one and the same place. Only in time can two contradictorily opposed predicates meet in one and the same object, namely, one after the other . Thus our concept of time explains the possibility of that body of a priori synthetic knowledge which is exhibited in the general doctrine of motion, and which is by no means unfruitful.
( a ) Time is not something which exists of itself, or which inheres in things as an objective determination, and it does not, therefore, remain when abstraction is made of all subjective conditions of its intuition. Were it self-subsistent, it would be something which would be actual and yet not an actual object. Were it a determination or order inhering in things themselves, it could not precede the objects as their condition, and be known and intuited a priori by means of synthetic propositions. But this 112 last is quite possible if time is nothing but the subjective condition under which alone 113 intuition can take place in us. For that being so, this form of inner intuition can be represented prior to the objects, and therefore a priori .
( b ) Time is nothing but the form of inner sense, that is, of the intuition of ourselves and of our inner state. It cannot be a determination of outer appearances; it has to do neither with shape nor position, but with the relation of representations in our inner state. And just because this inner intuition yields no shape, we endeavour to make up for this want by analogies. We represent the time-sequence by a line progressing to infinity, in which the manifold constitutes a series of one dimension only; and we reason from the properties of this line to all the properties of time, with this one exception, that while the parts of the line are simultaneous the parts of time are always successive. From this fact also, that all the relations of time allow of being expressed in an outer intuition, it is evident that the representation is itself an intuition.
( c ) Time is the formal a priori condition of all appearances whatsoever. Space, as the pure form of all outer intuition, is so far limited; it serves as the a priori condition only of outer appearances. But since all representations, whether they have for their objects outer things or not, belong, in themselves, as determinations of the mind, to our inner state; and since this inner state stands under the formal condition of inner intuition, and so belongs to time, time is an a priori condition of all appearance whatsoever. It is the immediate condition of inner appearances (of our souls), and thereby the mediate condition of outer appearances. Just as I can say a priori that all outer appearances are in space, and are determined a priori in conformity with the relations of space, I can also say, from the principle of inner sense, that all appearances whatsoever, that is, all objects of the senses, are in time, and necessarily stand in time-relations.
If we abstract from our mode of inwardly intuiting ourselves—the mode of intuition in terms of which we likewise take up into our faculty of representation 114 all outer intuitions—and so take objects as they may be in themselves, then time is nothing. It has objective validity only in respect of appearances, these being things which we take as objects of our senses . It is no longer objective, if we abstract from the sensibility of our intuition, that is, from that mode of representation which is peculiar to us, and speak of things in general . Time is therefore a purely subjective condition of our (human) intuition (which is always sensible, that is, so far as we are affected by objects), and in itself, apart from the subject, is nothing. Nevertheless, in respect of all appearances, and therefore of all the things which can enter into our experience, it is necessarily objective. We cannot say that all things are in time, because in this concept of things in general we are abstracting from every mode of their intuition and therefore from that condition under which alone objects can be represented as being in time. If, however, the condition be added to the concept, and we say that ail things as appearances, that is, as objects of sensible intuition, are in time, then the proposition has legitimate objective validity and universality a priori .
What we are maintaining is, therefore, the empirical reality of time, that is, its objective validity in respect of all objects which allow of ever being given to our senses. And since our intuition is always sensible, no object can ever be given to us in experience which does not conform to the condition of time. On the other hand, we deny to time all claim to absolute reality; that is to say, we deny that it belongs to things absolutely, as their condition or property, indepepdently of any reference to the form of our sensible intuition; properties that belong to things in themselves can never be given to us through the senses. This, then, is what constitutes the transcendental ideality of time. What we mean by this phrase is that if we abstract from the subjective conditions of sensible intuition, time is nothing, and cannot be ascribed to the objects in themselves (apart from their relation to our intuition) in the way either of subsistence or of inherence. This ideality, like that of space, must not, however, be illustrated by false analogies with sensation, 115 because it is then assumed that the appearance, in which the sensible predicates inhere, itself has objective reality. In the case of time, such objective reality falls entirely away, save in so far as it is merely empirical, that is, save in so far as we regard the object itself merely as appearance. On this subject, the reader may refer to what has been said at the close of the preceding section. 116
Against this theory, which admits the empirical reality of time, but denies its absolute and transcendental reality, I have heard men of intelligence so unanimously voicing an objection, that I must suppose it to occur spontaneously to every reader to whom this way of thinking is unfamiliar. The objection is this. Alterations 118 are real, 3 119 this being proved by change 120 of our own representations—even if all outer appearances, together with their alterations, be denied. Now alterations are possible only in time, and time is therefore something real. There is no difficulty in meeting this objection. I grant the whole argument. Certainly time is something real, namely, the real form of inner intuition. It has therefore subjective reality in respect of inner experience; that is, I really have the representation of time and of my determinations in it. Time is therefore to be regarded as real, not indeed as object but as the mode of representation of myself as object. If without this condition of sensibility I could intuit myself, or be intuited by another being, the very same determinations which we now represent to ourselves as alterations would yield knowledge into which the representation of time, and therefore also of alteration, would in no way enter. Thus empirical reality has to be allowed to time, as the condition of all our experiences; on our theory, it is only its absolute reality that has to be denied. It is nothing but the form of our inner intuition. 121 If we take away from our inner intuition the peculiar condition of our sensibility, the concept of time likewise vanishes; it does not inhere in the objects, but merely in the subject which intuits them.
But the reason why this objection is so unanimously urged, and that too by those who have nothing very convincing to say against the doctrine of the ideality of space, is this. They have no expectation of being able to prove apodeictically the absolute reality of space; for they are confronted by idealism, which teaches that the reality of outer pbjects does not allow of strict proof. On the other hand, the reality of the object of our inner sense (the reality of myself and my state) is, [they argue,] immediately evident through consciousness. The former may be merely an illusion; the latter is, on their view, undeniably something real. What they have failed, however, to recognise is that both are in the same position; in neither case can their reality as representations be questioned, and in both cases they belong only to appearance, which always has two sides, the one by which the object is viewed in and by itself (without regard to the mode of intuiting it—its nature therefore remaining always problematic), the other by which the form of the intuition of this object is taken into account. This form is not to be looked for in the object in itself, but in the subject to which the object appears; nevertheless, it belongs really and necessarily to the appearance of this object.
Time and space are, therefore, two sources of knowledge, from which bodies of a priori synthetic knowledge can be derived. (Pure mathematics is a brilliant example of such knowledge, especially as regards space and its relations.) Time and space, taken together, are the pure forms of all sensible intuition, and so are what make a priori synthetic propositions possible. But these a priori sources of knowledge, being merely conditions of our sensibility, just by this very fact determine their own limits, namely, that they apply to objects only in so far as objects are viewed as appearances, and do not present things as they are in themselves. This is the sole field of their validity; should we pass beyond it, no objective use can be made of them. This ideality 122 of space and time leaves, however, the certainty of empirical knowledge unaffected, for we are equally sure of it, whether these forms necessarily inhere in things in themselves or only in our intuition of them. Those, on the other hand, who maintain the absolute reality of space and time, whether as subsistent 123 or only as inherent, must come into conflict with the principles of experience itself. For if they decide for the former alternative (which is generally the view taken by mathematical students of nature), they have to admit two eternal and infinite self-subsistent 124 non-entities 125 (space and time), which are there (yet without there being anything real) only in order to contain in themselves all that is real. If they adopt the latter alternative (as advocated by certain metaphysical students of nature), and regard space and time as relations of appearances, alongside or in succession to one another—relations abstracted from experience, and in this isolation confusedly represented—they are obliged to deny that a priori mathematical doctrines have any validity in respect of real things (for instance, in space), or at least to deny their apodeictic certainty. For such certainty is not to be found in the a posteriori . On this view, indeed, the a priori concepts of space and time are merely creatures of the imagination, whose source must really be sought in experience, the imagination framing out of the relations abstracted from experience something that does indeed contain what is general in these relations, but which cannot exist without the restrictions which nature has attached to them. The former thinkers obtain at least this advantage, that they keep the field of appearances open for mathematical propositions. On the other hand, they have greatly embarrassed themselves by those very conditions [space and time, eternal, infinite, and self-subsistent], when with the understanding they endeavour to go out beyond this field. The latter have indeed an advantage, in that the representations of space and time do not stand in their way if they seek to judge of objects, not as appearances but merely in their relation to the understanding. But since they are unable to appeal to a true and objectively valid a priori intuition, they can neither account for the possibility of a priori mathematical knowledge, nor bring the propositions of experience into necessary agreement with it. On our theory of the true character of these two original forms of sensibility, both difficulties are removed.
Lastly, transcendental aesthetic cannot contain more than these two elements, space and time. This is evident from the fact that all other concepts belonging to sensibility, even that of motion, in which both elements are united, presuppose something empirical. Motion presupposes the perception of something movable. But in space, considered in itself, there is nothing movable; consequently the movable must be something that is found in space only through experience , and must therefore be an empirical datum. For the same reason, transcendental aesthetic cannot count the concept of change among its a priori data. Time itself does not change, but only something which is in time. The concept of time thus presupposes the perception of something existing and of the succession of its determinations; that is to say, it presupposes experience.
I. 1 To avoid all misapprehension, it is necessary to explain, as clearly as possible, what our view is regarding the fundamental constitution of sensible knowledge in general.
What we have meant to say is that all our intuition is nothing but the representation of appearance; that the things which we intuit are not in themselves what we intuit them as being, nor their relations so constituted in themselves as they appear to us, and that if the subject, or even only the subjective constitution of the senses in general, be removed, the whole constitution and all the relations of objects in space and time, nay space and time themselves, would vanish. As appearances, they cannot exist in themselves, but only in us. What objects may be in themselves, and apart from all this receptivity of our sensibility, remains completely unknown to us. We know nothing but our mode of perceiving them—a mode which is peculiar to us, and not necessarily shared in by every being, though, certainly, by every human being. With this alone have we any concern. Space and time are its pure forms, and sensation in general its matter. The former alone can we know a priori that is, prior to all actual perception; and such knowledge is therefore called pure intuition. The latter is that in our knowledge which leads to its being called a posteriori knowledge, that is, empirical intuition. The former inhere in our sensibility with absolute necessity, no matter of what kind our sensations may be; the latter can exist in vailing modes. Even if we could bring our intuition to the highest degree of clearness, we should not thereby come any nearer to the constitution of objects in themselves. We should still know only our mode of intuition, that is, our sensibility. We should, indeed, know it completely, but always only under the conditions of space and time—conditions which are originally inherent in the subject. What the objects may be in themselves would never become known to us even through the most enlightened knowledge of that which is alone given us, namely, their appearance.
The concept of sensibility and of appearance would be falsified, and our whole teaching in regard to them would be rendered empty and useless, if we were to accept the view that our entire sensibility is nothing but a confused representation of things, containing only what belongs to them in themselves, but doing so under an aggregation of characters and partial representations that we do not consciously distinguish. For the difference between a confused and a clear representation is merely logical, and does not concern the content. No doubt the concept of ‘right’, 127 in its common-sense usage, contains all that the subtlest speculation can develop out of it, though in its ordinary and practical use we are not conscious of the manifold representations comprised in this 128 thought. But we cannot say that the common concept is therefore sensible, containing a mere appearance. For ‘right’ can never be an appearance; it is a concept in the understanding, and represents a property (the moral property) of actions, which belongs to them in themselves. The representation of a body in intuition, on the other hand, contains nothing that can belong to an object in itself, but merely the appearance of something, and the mode in which we are affected by that something; and this receptivity of our faculty of knowledge is termed sensibility. Even if that appearance could become completely transparent to us, such knowledge would remain toto coelo different from knowledge of the object in itself.
The philosophy of Leibniz and Wolff, in thus treating the difference between the sensible and the intelligible as merely logical, has given a completely wrong direction to all investigations into the nature and origin of our knowledge. This difference is quite evidently transcendental. It does not merely concern their [logical] form, as being either clear or confused. It concerns their origin and content. It is not that by our sensibility we cannot know the nature of things in themselves in any save a confused fashion; we do not apprehend them in any fashion whatsoever. If our subjective constitution be removed, the represented object, with the qualities which sensible intuition bestows upon it, is nowhere to be found, and cannot possibly be found. For it is this subjective constitution which determines its form as appearance.
We commonly distinguish in appearances that which is essentially inherent in their intuition and holds for sense in all human beings, from that which belongs to their intuition accidentally only, and is valid not in relation to sensibility in general but only in relation to a particular standpoint or to a peculiarity of structure in this or that sense. The former kind of knowledge is then declared to represent the object in itself, the latter its appearance only. But this distinction is merely empirical. If, as generally happens, we stop short at this point, and do not proceed, as we ought, to treat the empirical intuition as itself mere appearance, in which nothing that belongs to a thing in itself can be found, our transcendental distinction is lost. We then believe that we know things in themselves, and this in spite of the fact that in the world of sense, however deeply we enquire into its objects, we have to do with nothing but appearances. The rainbow in a sunny shower may be called a mere appearance, and the rain the thing in itself. This is correct, if the latter concept be taken in a merely physical sense. Rain will then be viewed only as that which, in all experience and in all its various positions relative to the senses, is determined thus, and not otherwise, in our intuition. But if we take this empirical object in its general character, and ask, without considering whether or not it is the same for all human sense, whether it represents an object in itself (and by that we cannot mean the drops of rain, for these are already, as appearances, empirical objects), the question as to the relation of the representation to the object at once becomes transcendental. We then realise that not only are the drops of rain mere appearances, but that even their round shape, nay even the space in which they fall, are nothing in themselves, but merely modifications or fundamental forms of our sensible intuition, and that the transcendental object remains unknown to us.
The second important concern of our Transcendental Aesthetic is that it should not obtain favour merely as a plausible hypothesis, but should have that certainty and freedom from doubt which is required of any theory that is to serve as an organon. To make this certainty completely convincing, we shall select a case by which the validity of the position adopted will be rendered obvious, and which will serve to set what has been said in § 3 in a clearer light.
Let us suppose that space and time are in themselves objective, and are conditions of the possibility of things in themselves. In the first place, it is evident that in regard to both there is a large number of a priori apodeictic and synthetic propositions. This is especially true of space, to which our chief attention will therefore be directed in this enquiry. Since the propositions of geometry are synthetic a priori and are known with apodeictic certainty, I raise the question, whence do you obtain such propositions, and upon what does the understanding rely in its endeavour to achieve such absolutely necessary and universally valid truths? There is no other way than through concepts or through intuitions; and these are given either a priori or a posteriori . In their latter form, namely, as empirical concepts, and also as that upon which these are grounded, the empirical intuition, neither the concepts nor the intuitions can yield any synthetic proposition except such as is itself also merely empirical (that is, a proposition of experience), and which for that very reason can never possess the necessity and absolute universality which are characteristic of all geometrical propositions. As regards the first and sole means of arriving at such knowledge, namely, in a priori fashion through mere concepts or through intuitions, it is evident that from mere concepts only analytic knowledge, not synthetic knowledge, is to be obtained. Take, for instance, the proposition, “Two straight lines cannot enclose a space, and with them alone no figufe is possible”, and try to derive it from the concept of straight lines and of the number two. Or take the proposition, “Given three straight lines, a figure is possible”, and try, in like manner, to derive it from the concepts involved. All your labour is vain; and you find that you are constrained to have recourse to intuition, as is always done in geometry. You therefore give yourself an object in intuition. But of what kind is this intuition? Is it a pure a priori intuition or an empirical intuition? Were it the latter, no universally valid proposition could ever arise out of it—still less an apodeictic proposition—for experience can never yield such. You must therefore give yourself an object a priori in intuition, and ground upon this your synthetic proposition. If there did not exist in you a power of a priori intuition; and if that subjective condition were not also at the same time, as regards its form, the universal a priori condition under which alone the object of this outer intuition is itself possible; if the object (the triangle) were something in itself, apart from any relation to you, the subject, how could you say that what necessarily exist in you as subjective conditions for the construction of a triangle, must of necessity belong to the triangle itself? You could not then add anything new (the figure) to your concepts (of three lines) as something which must necessarily be met with in the object, since this object is [on that view] given antecedently to your knowledge, and not by means of it. If, therefore, space (and the same is true of time) were not merely a form of your intuition, containing conditions a priori , under which alone things can be outer objects to you, and without which subjective conditions outer objects are in themselves 129 nothing, you could not in regard to outer objects determine anything whatsoever in an a priori and synthetic manner. It is, therefore, not merely possible or probable, but indubitably certain, that space and time, as the necessary conditions of all outer and inner experience, are merely subjective conditions of all our intuition, and that in relation to these conditions all objects are therefore mere appearances, and not given us as things in themselves which exist in this manner. For this reason also, while much can be said a priori as regards the form of appearances, nothing whatsoever can be asserted of the thing in itself, which may underlie these appearances.
II. 130 In confirmatitm of this theory of the ideality of both outer and inner sense, and therefore of all objects of the senses, as mere appearances, it is especially relevant to observe that everything in our knowledge which belongs to intuition—feeling of pleasure and pain, and the will, not being knowledge, are excluded—contains nothing but mere relations; namely, of locations in an intuition (extension), of change of location (motion), and of laws according to which this change is determined (moving forces). What it is that is present in this or that location, or what it is that is operative 131 in the things themselves apart from change of location, is not given through intuition. Now a thing in itself 132 cannot be known through mere relations; and we may therefore conclude that since outer sense gives us nothing but mere relations, this sense can contain in its representation only the relation of an object to the subject, and not the inner properties of the object in itself. This also holds true of inner sense, not only because the representations of the outer senses constitute the proper material with which we occupy our mind, but because the time in which we set these representations, which is itself antecedent to the consciousness of them in experience, and which underlies them as the formal condition of the mode in which we posit 133 them in the mind, itself contains [only] relations of succession, coexistence, and of that which is coexistent with succession, the enduring. Now that which, as representation, can be antecedent to any and every act of thinking anything, is intuition; and if it contains nothing but relations, it is the form of intuition. Since this form does not represent anything save in so far as something is posited in the mind, it can be nothing but the mode in which the mind is affected through its own activity (namely, through this positing of its 5 134 representation), and so is affected by itself; in other words, it is nothing but an inner sense in respect of the form of that sense. Everything that is represented through a sense is so far always appearance, and consequently we must either refuse to admit that there is an inner sense, or we must recognise that the subject, which is the object of the sense, can be represented through it only as appearance, not as that subject would judge of itself if its intuition were self-activity only, that is, were intellectual. The whole difficulty is as to how a subject can inwardly intuit itself; and this is a difficulty common to every theory. The consciousness of self (apperception) is the simple representation of the ‘I’, and if all that is manifold in the subject were given by the activity of the self , the inner intuition would be intellectual. In man this consciousness demands inner perception of the manifold which is antecedently given in the subject, and the mode in which this manifold is given in the mind must, as non-spontaneous, be entitled sensibility. If the faculty of coming to consciousness of oneself is to seek out (to apprehend) that which lies in the mind, it must affect the mind, and only in this way can it give rise to an intuition of itself. But the form of this intuition, which exists antecedently in the mind, determines, in the representation of time, the mode in which the manifold is together in the mind, since it then intuits itself not as it would represent itself if immediately self-active, but as it is affected by itself, and therefore as it appears to itself, not as it is.
III. When I say that the intuition of outer objects and the self-intuition of the mind alike represent the objects and the mind, in space and in time, as they affect our senses, that is, as they appear, I do not mean to say that these objects are a mere illusion. 135 For in an appearance the objects, nay even the properties that we ascribe to them, are always regarded as something actually given. Since, however, in the relation of the given object to the subject, such properties depend upon the mode of intuition of the subject, this object as appearance 136 is to be distinguished from itself as object in itself . Thus when I maintain that the quality of space and of time, in conformity with which, as a condition of their existence, I posit both bodies and my own soul, lies in my mode of intuition and not in those objects in themselves, I am not saying that bodies merely seem 137 to be outside me, or that my soul only seems to be given in myself-consciousness. It would be my own fault, if out of that which I ought to reckon as appearance, I made mere illusion. 138 That does not follow as a consequence of our principle of the ideality of all our sensible intuitions—quite the contrary. It is only if we ascribe objective reality to these forms of representation, that it becomes impossible for us to prevent everything being thereby transformed into mere illusion , For if we regard space and time as properties which, if they are to be possible at all, 139 must be found in things in themselves, and if we reflect on the absurdities in which we are then involved, in that two infinite things, which are not substances, nor anything actually inhering in substances, must yet have existence, nay, must be the necessary condition of the existence of all things, and moreover must continue to exist, even although all existing things be removed,—we cannot blame the good Berkeley for degrading bodies to mere illusion. Nay, even our own existence, in being made thus dependent upon the self-subsistent reality of a non-entity, such as time, would necessarily be changed with it into sheer illusion—an absurdity of which no one has yet been guilty.
IV. In natural theology, in thinking an object [God], who not only can never be an object of intuition to us but cannot be an object of sensible intuition even to himself, we are careful to remove the conditions of time and space from his intuition—for all his knowledge must be intuition, and not thought , which always involves limitations. But with what right can we do this if we have previously made time and space forms of things in themselves, and such as would remain, as a priori conditions of the existence of things, even though the things themselves were removed? As conditions of all existence in general, they must also be conditions of the existence of God. If we do not thus treat them as objective forms of all things, the only alternative is to view them as subjective forms of our inner and outer intuition, which is termed sensible, for the very reason that it is not original , that is, is not such as can itself give us the existence of its object—a mode of intuition which, so far as we can judge, can belong only to the primordial being. 140 Our mode of intuition is dependent upon the existence of the object, and is therefore possible only if the subject’s faculty of representation is affected by that object.
This mode of intuiting in space and time need not be limited to human sensibility. It may be that all finite, thinking beings necessarily agree with man in this respect, although we are not in a position to judge whether this is actually so. But however universal this mode of sensibility may be, it does not therefore cease to be sensibility. It is derivative ( intuitus derivativus ), not original ( intuitus originarius ), and therefore not an intellectual intuition. For the reason stated above, such intellectual intuition seems to belong solely to the primordial being, and can never be ascribed to a dependent being, dependent in its existence as well as in its intuition, and which through that intuition determines its existence solely in relation to given objects. 141 This latter remark, however, must be taken only as an illustration of our aesthetic theory, not as forming part of the proof.
Here, then, in pure a priori intuitions, space and time, we have one of the factors required for solution of the general problem of transcendental philosophy: how are synthetic a priori judgments possible? When in a priori judgment we seek to go out beyond the given concept, we come in the a priori intuitions upon that which cannot be discovered in the concept but which is certainly found a priori in the intuition corresponding to the concept, and can be connected with it synthetically. Such judgments, however, thus based on intuition, can never extend beyond objects of the senses; they are valid only for objects of possible experience.