Critique of Pure Reason

by Immanuel Kant

  The proposition I think, if it means I exist thinking, is not merely logical function, but determines the subject (which then is at the same time object) with reference to its existence, and is impossible without the internal sense, the intuition of which always supplies the object, not as a thing by itself, but as phenomenal only. Here, therefore, we have no longer mere spontaneity of thinking, but also receptivity of intuition, that is, the thinking of myself applied to the empirical intuition of the same subject. In that empirical intuition the thinking self would have to look for the conditions under which its logical functions can be employed as categories of substance, cause, etc., in order not only to distinguish itself as an object by itself, through the Ego, but to determine the mode of its existence also, that is, to know itself as a noumenon. This, as we know, is impossible, because the internal empirical intuition is sensuous, and supplies us with phenomenal data only, which furnish nothing to the object of the pure consciousness for the knowledge of its own separate existence, but can serve the purpose of experience only.

  Supposing, however, that we should hereafter discover, not indeed in experience, but in certain (not only logical rules, but) a priori established laws of pure reason, concerning our existence, some ground for admitting ourselves, entirely a priori, as determining and ruling our own existence, there would then be a spontaneity by which our reality would be determinable without the conditions of empirical intuition, and we should then perceive that in the consciousness of our existing there is contained a priori something which may serve to determine with respect to some inner faculty, our existence, which otherwise can be determined sensuously only with reference to an intelligible, though, of course, an ideal world only.

  This, however, would not in the least benefit the attempts of rational psychology. For though through that wonderful faculty, which becomes first revealed to myself by the consciousness of a moral law, I should have a principle, purely intellectual, for a determination of my existence, what would be its determining predicates? No other but those which must be given to me in sensuous intuition; and I should therefore find myself again in the same situation where I was before in rational psychology, requiring sensuous intuitions in order to give significance to the concepts of my understanding, such as substance, cause, etc., by which alone I can gain a knowledge of myself; and these intuitions can never carry me beyond the field of experience. Nevertheless, for practical purposes, which always concern objects of experience, I should be justified in applying these concepts, in analogy with their theoretical employment, to liberty also and to the subject of liberty, by taking them only as logical functions of subject and predicate,33 of cause and effect. According to them, acts or effects, as following those (moral) laws, would be so determined that they may together with the laws of nature be explained in accordance with the categories of substance and cause; though arising in reality from a totally different principle. All this is only meant to prevent a misunderstanding to which our doctrine, which represents self-intuition as purely phenomenal, might easily be exposed. In what follows we shall have occasion to make good use of it.

  Supplement XXVIII

  I Have sometimes called it formal idealism also, in order to distinguish it from the material or common idealism, which doubts or denies the very existence of external things. In some cases it seems advisable to use these terms rather than those in the text, in order to prevent all misunderstanding. (This is an additional note in the Second Edition.)

  1 Kant himself in a letter to Schütz (Darstellung seines Lebens von seinem Sohn, Halle, 1835, Band. II. S. 208) pointed out the mistake which appears in the preface to the 2nd edition, namely, gleichseitig (equilateral), instead of gleichschenkelig (isosceles).

  2 I am not closely following here the course of the history of the experimental method, nor are the first beginnings of it very well known.

  3 This method, borrowed from the student of nature, consists in our looking for the elements of pure reason in that which can be confirmed or refuted by experiment. Now it is impossible, in order to test the propositions of pure reason, particularly if they venture beyond all the limits of possible experience, to make any experiment with their objects (as in natural science); we can therefore only try with concepts and propositions which we admit a priori, by so contriving that the same objects may be considered on one side as objects of the senses and of the understanding in experience, and, on the other, as objects which are only thought, intended, it may be, for the isolated reason which strives to go beyond all the limits of experience. This gives us two different sides to be looked at; and if we find that, by looking on things from that twofold point of view, there is an agreement with the principle of pure reason, while by admitting one point of view only, there arises an inevitable conflict with reason, then the experiment decides in favour of the correctness of that distinction.

  4 This experiment of pure reason has a great similarity with that of the chemists, which they sometimes call the experiment of reduction, or the synthetical process in general. The analysis of the metaphysician divided pure knowledge a priori into two very heterogeneous elements, namely, the knowledge of things as phenomena and of things by themselves. Dialectic combines these two again, to bring them into harmony with the necessary idea of the unconditioned, demanded by reason, and then finds that this harmony can never be obtained, except through the above distinction, which therefore must be supposed to be true.

  5 In the same manner the laws of gravity, determining the movements of the heavenly bodies, imparted the character of established certainty to what Copernicus had assumed at first as an hypothesis only, and proved at the same time the invisible force (the Newtonian attraction) which holds the universe together, which would have remained for ever undiscovered, if Copernicus had not dared, by an hypothesis, which, though contradicting the senses, was yet true, to seek the observed movements, not in the heavenly bodies, but in the spectator. I also propose in this preface my own view of metaphysics, which has so many analogies with the Copernican hypothesis, as an hypothesis only, though, in the Critique itself, it is proved by means of our representations of space and time, and the elementary concepts of the understanding, not hypothetically, but apodictically; for I wish that people should observe the first attempts at such a change, which must always be hypothetical.

  6 In order to know an object, I must be able to prove its possibility, either from its reality, as attested by experience, or a priori by means of reason. But I can think whatever I please, provided only I do not contradict myself, that is, provided my conception is a possible thought, though I may be unable to answer for the existence of a corresponding object in the sum total of all possibilities. Before I can attribute to such a concept objective reality (real possibility, as distinguished from the former, which is purely logical), something more is required. This something more, however, need not be sought for in the sources of theoretical knowledge, for it may be found in those of practical knowledge also.

  7 The only thing which might be called an addition, though in the method of proof only, is the new refutation of psychological idealism, and the strict (and as I believe the only possible) proof of the objective reality of external phenomena on p. 275 (Suppl. XXI). That idealism may be considered entirely innocent with respect to the essential aims of metaphysic (though it is not so in reality), yet it remains a scandal to philosophy, and to human reason in general, that we should have to accept the existence of things without us (from which we derive the whole material of knowledge for our own internal sense) on faith only, unable to meet with any satisfactory proof an opponent, who is pleased to doubt it. (See p. 476.) It will probably be urged against this proof that, after all, I am immediately conscious of that only which is within me, that is, of my representation of external things, and that consequently it must still remain uncertain whether there be outside me anything corresponding to it or not. But by internal experience I am conscious of my existence in time (consequently also, of its determinab
ility in time); and this is more than to be conscious of my representation only, and yet identical with the empirical consciousness of my existence, which can be itself determined only by something connected with my existence, yet outside me. This consciousness of my existence in time is therefore connected as identical with the consciousness of relation to something outside me; so that it is experience, and not fiction, sense, and not imagination, which indissolubly connects the external with my internal sense. The external sense is by itself a relation of intuition to something real outside me; and its real, in contradistinction to a purely imaginary character, rests entirely on its being indissolubly connected with internal experience, as being the condition of its possibility. This is what happens here. If with the intellectual consciousness of my existence in the representation, I am, which accompanies all my judgments and all acts of my understanding, I could at the same time connect a determination of that existence of mine by means of intellectual intuition, then that determination would not require the consciousness of relation to something outside me. But although that intellectual consciousness comes first, the inner intuition, in which alone any existence can be determined, is sensuous and dependent on the condition of time; and that determination again, and therefore internal experience itself, depends on something permanent which is not within me, consequently on something outside me only, to which I must consider myself as standing in a certain relation. Hence the reality of the external sense is necessarily connected, in order to make experience possible at all, with the reality of the internal sense; that is, I am conscious, with the same certainty, that there are things outside me which have a reference to my sense, as that I exist myself in time. In order to ascertain to what given intuitions objects outside me really correspond (these intuitions belonging to the external sense, and not to the faculty of imagination), we must in each single case apply the rules according to which experience in general (even internal) is distinguished from imaginations, the proposition that there really is an external experience being always taken for granted. It may be well to add here the remark that the representation of something permanent in existence is not the same as permanent representation; for this (the representation of something permanent in existence) can change and alternate, as all our representations, even those of matter, and may yet refer to something permanent, which must therefore be something external, and different from all my representations, the existence of which is necessarily involved in the determination of my own existence, and constitutes with it but one experience, which could never take place internally, unless (in part) it were external also. The how admits here of as little explanation as the permanent in time in general, the co-existence of which with the variable produces the concept of change.

  8 According to an emendation adopted both by Vaihinger and Adickes.

  9 This paragraph from It is true to intuition seems to have been a marginal note, as shown by Dr. Vaihinger. See Translator's Preface, p. lii.

  10 One might doubt this with regard to pure natural science; but one has only to consider the different propositions which stand at the beginning of real (empirical) physical science, those, for example, relating to the permanence of the same quantity of matter to the vis inertiae, the equality of action and reaction, etc., in order to become convinced that they constitute a physica pura, or rationalis, which well deserves to stand by itself as an independent science, in its whole extent, whether narrow or wide.

  11 Phenomenal predicates can be attributed to the object in its relation to our sense: as for instance to the rose its red colour, and its scent. But what is merely illusion can never be attributed to an object as a predicate, for the simple reason that the illusion attributes to the object by itself something which belongs to it only in its relation to the senses, or to a subject in general: as for instance the two handles, which were formerly attributed to Saturn. That which is never to be found in the object itself, but always in its relation to a subject, and is inseparable from its representation by a subject, is phenomenal, and the predicates of space and time are therefore rightly attributed to objects of the senses, as such. In this there is no illusion. If, on the contrary, I were to attribute to the rose by itself redness, handles to Saturn, and extension to all external objects, without restricting my judgment to the relation of these objects to a subject, we should have illusion.

  12 Metaphysical Elements of Natural Science.

  13 Whether the representations themselves are identical, and whether therefore one can be thought analytically by the other, is a matter of no consequence here. The consciousness of the one has always to be distinguished from the consciousness of the other, so far as the manifold is concerned; and everything here depends on the synthesis only of this (possible) consciousness.

  14 This analytical unity of consciousness belongs to all general concepts, as such. If, for instance, I think red in general, I represent to myself a property, which (as a characteristic mark) may be found in something, or can be connected with other representations; that is to say, only under a presupposed possible synthetical unity can I represent to myself the analytical. A representation which is to be thought as common to different representations, is looked upon as belonging to such as possess, besides it, something different. It must therefore have been thought in synthetical unity with other (though only possible) representations, before I can think in it that analytical unity of consciousness which makes it a conceptus communis. The synthetical unity of apperception is, therefore, the highest point with which all employment of the understanding, and even the whole of logic, and afterwards the whole of transcendental philosophy, must be connected; ay, that faculty is the understanding itself.

  15 Space and time, and all portions thereof, are intuitions, and consequently single representations with the manifold of their content. (See the transcendental Æsthetic.) They are not, therefore, mere concepts, through which the same consciousness, as existing in many representations, but intuitions through which many representations are brought to us, as contained in one and in its consciousness; this latter, therefore, is compounded, and these intuitions represent the unity of consciousness as synthetical, but yet as primitive. This character of singleness in them is practically of great importance (see § 25).

  16 The lengthy doctrine of the four syllogistic figures concerns categorical syllogisms only, and though it is really nothing but a trick for obtaining the appearance of more modes of concluding than that of the first figure, by secretly introducing immediate conclusions (consequentiae immediatae) among the premisses of a pure syllogism, this would hardly have secured its great success, had not its authors succeeded, at the same time, in establishing the exclusive authority of categorical judgments, as those to which all others must be referred. This as we showed in § 9, p. 62, is wrong.

  17 The proof of this rests on the represented unity of intuition, by which an object is given, and which always includes a synthesis of the manifold which is given for an intuition, and contains the relation of the latter to the unity of apperception.

  18 Motion of an object in space does not belong to a pure science, consequently not to geometry, because the fact that a thing is moveable cannot be known a priori, but from experience only. Motion, however, considered as describing a space, is a pure act of successive synthesis of the manifold in external intuition in general by means of productive imagination, and belongs therefore, by right, not only to geometry, but even to transcendental philosophy.

  19 I do not see how so much difficulty should be found in admitting that the internal sense is affected by ourselves. Every act of attention gives us an instance of it. In such an act the understanding always determines the internal sense, according to the connection which it thinks, to such an internal intuition as corresponds to the manifold in the synthesis of the understanding. How much the mind is commonly affected thereby anybody will be able to perceive in himself.

  20 The I think expresses the act of determining my own existence. What is thus giv
en is the existence, but what is not yet given, is the manner in which I am to determine it, that is, in which I am to place within me the manifold belonging to it. For that purpose self-intuition is required, which depends on an a priori form, that is, on time, which is sensuous, and belongs to our receptivity of what is given to us as determinable. If, then, I have not another self-intuition which, likewise before the act of determination, gives the determining within me, of the spontaneity of which I am conscious only, as time gives the determinable, I cannot determine my existence as that of a spontaneously acting being, but I only represent to myself the spontaneity of my thinking, that is, of the act of determination, my existence remaining sensuous only, that is, determinable, as the existence of a phenomenon. It is, however, on account of this spontaneity that I call myself an intelligence.

  21 Space, represented as an object (as required in geometry), contains more than the mere form of intuition, namely, the comprehension of the manifold, which is given according to the form of sensibility, into a perceptible (intuitable) representation, so that the form of intuition gives the manifold only, while the formal intuition gives unity of representation. In the Æsthetic I had simply ascribed this unity to sensibility, in order to show that it precedes all concepts, though it presupposes a synthesis not belonging to the senses, and by which all concepts of space and time become first possible. For as by that synthesis (the understanding determining the sensibility) space and time are first given as intuitions, the unity of that intuition a priori belongs to space and time, and not to the concept of the understanding. (See § 24.)