The Online Library of Liberty

A project of Liberty Fund, Inc.

• Dedication
• Preface 1
• Translator’s Preface
• Translator’s Preface to Second Edition
• Introduction [p. 1]
• I: The Idea of Transcendental Philosophy
• II: Division of Transcendental Philosophy
• I: The Elements of Transcendentalism
• Part I: Transcendental Æsthetic [p. 19]
• Section I: Of Space
• Section II: Of Time
• Part II: Transcendental Logic [p. 50]
• Introduction the Idea of a Transcendental Logic
• I: Of Logic In General
• II: Of Transcendental Logic
• III: Of the Division of General Logic Into Analytic and Dialectic
• IV: Of the Division of Transcendental Logic Into Transcendental Analytic and Dialectic
• Division I: Transcendental Analytic In Two Books, With Their Chapters and Sections
• Book I: Analytic of Concepts
• Chapter I: Method of Discovering All Pure Concepts of the Understanding
• Section I: Of the Logical Use of the Understanding In General
• Section II: Of the Logical Function of the Understanding In Judgments [p. 70]
• Section III: Of the Pure Concepts of the Understanding, Or of the Categories
• Chapter II: Of the Deduction of the Pure Concepts of the Understanding [p. 84]
• Section I: Of the Principles of a Transcendental Deduction In General
• Section II: Of the a Priori Grounds For the Possibility of Experience
• I: Of the Synthesis of Apprehension In Intuition
• II: Of the Synthesis of Reproduction In Imagination
• III: Of the Synthesis of Recognition In Concepts [p. 103]
• IV: Preliminary Explanation of the Possibility of the Categories As Knowledge a Priori
• Section III: Of the Relation of the Understanding to Objects In General, and the Possibility of Knowing Them a Priori [p. 115]
• Book II: Analytic of Principles
• Introduction of the Transcendental Faculty of Judgment In General
• Chapter I: Of the Schematism of the Pure Concepts of the Understanding [p. 137]
• Chapter II: System of All Principles of the Pure Understanding [p. 148]
• Section I: Of the Highest Principle of All Analytical Judgments
• Section II: Of the Highest Principle of All Synthetical Judgments [p. 154]
• Section III: Systematical Representation of All Synthetical Principles of the Understanding
• I: [of the Axioms of Intuition 1 Principle of the Pure Understanding
• II: [ Anticipations of Perception
• III: [ the Analogies of Experience
• IV: The Postulates of Empirical Thought In General
• Chapter III: On the Ground of Distinction of All Subjects Into Phenomena and Noumena
• I.: Identity and Difference
• II.: Agreement and Opposition
• III.: The Internal and the External
• IV.: Matter and Form
• Note On the Amphiboly of Reflective Concepts
• Division II: Transcendental Dialectic In Two Books, With Their Chapters and Sections [p. 293]
• Introduction: 1.
• Book I: Of the Concepts of Pure Reason [p. 310]
• First Section of Ideas In General
• Second Section of Transcendental Ideas [p. 321]
• Third Section System of Transcendental Ideas [p. 333]
• Book II: Of the Dialectical Conclusions of Pure Reason
• Chapter I: Of the Paralogisms of Pure Reason [p. 341]
• Chapter II: The Antinomy of Pure Reason
• Section I: System of Cosmological Ideas
• Section II: Antithetic of Pure Reason
• Section III: Of the Interest of Reason In These Conflicts [p. 462]
• Section IV: Of the Transcendental Problems of Pure Reason, and the Absolute Necessity of Their Solution
• Section V: Sceptical Representation of the Cosmological Questions In the Four Transcendental Ideas [p. 485]
• Section VI: Transcendental Idealism As the Key to the Solution of Cosmological Dialectic
• Section VII: Critical Decision of the Cosmological Conflict of Reason With Itself
• Section VIII: The Regulative Principle of Pure Reason With Regard to the Cosmological Ideas [p. 508]
• Section IX: Of the Empirical Use of the Regulative Principle of Reason With Regard to All Cosmological Ideas
• Chapter III: The Ideal of Pure Reason
• Section I: Of the Ideal In General
• Section II: Of the Transcendental Ideal ( Prototypon Transcendentale )
• Section III: Of the Arguments of Speculative Reason In Proof of the Existence of a Supreme Being
• Section IV: Of the Impossibility of an Ontological Proof of the Existence of God [p. 592]
• Section V: Of the Impossibility of a Cosmological Proof of the Existence of God [p. 603]
• Section VI: Of the Impossibility of the Physico-theological Proof
• Section VII: Criticism of All Theology Based On Speculative Principles of Reason [p. 631]
• Chapter I: The Discipline of Pure Reason
• Section I: The Discipline of Pure Reason In Its Dogmatical Use
• Section II: The Discipline of Pure Reason In Its Polemical Use
• Section III: The Discipline of Pure Reason With Regard to Hypotheses
• Section IV: The Discipline of Pure Reason With Regard to Its Proofs
• Chapter II: The Canon of Pure Reason [p. 795]
• First Section: of the Ultimate Aim of the Pure Use of Our Reason
• Section II: Of the Ideal of the Summum Bonum As Determining the Ultimate Aim of Pure Reason
• Section III: Of Trowing, Knowing, and Believing [p. 820]
• Chapter III: The Architectonic of Pure Reason [p. 832]
• Chapter IV: The History of Pure Reason [p. 852]
• Supplement I: Motto to Second Edition
• Supplement II: Preface to the Second Edition. 1787. [p. Vii]
• Supplement III: Supplement Iv
• Supplement V
• Supplement Vi
• Supplement V
• Supplement Vi
• Supplement Vii
• Supplement Viii
• Supplement Ix
• Supplement X
• Supplement Xi
• Supplement Xii
• Supplement Xiii
• Supplement Xiv
• Supplement Xv
• Supplement Xvi a
• Supplement Xvi B
• Supplement Xvii
• Supplement Xviii
• Supplement Xix
• Supplement Xx
• Supplement Xxi
• Supplement Xxii
• Supplement Xxiii
• Supplement Xxiv
• Supplement Xxv
• Supplement Xxvi
• Supplement Xxvii
• Supplement Xxviii

Chapter I

The Discipline of Pure Reason

Negative judgments, being negative not only in their logical form, but in their contents also, do not enjoy a very high reputation among persons desirous of increasing human knowledge. They are even looked upon as jealous enemies of our never-ceasing desire for [p. 709] knowledge, and we have almost to produce an apology, in order to secure for them toleration, or favour and esteem.

No doubt, all propositions may logically be expressed as negative: but when we come to the question whether the contents of our knowledge are enlarged or restricted by a judgment, we find that the proper object of negative judgments is solely to prevent error. Hence negative propositions, intended to prevent erroneous knowledge in cases where error is never possible, may no doubt be very true, but they are empty, they do not answer any purpose, and sound therefore often absurd; like the well-known utterance of a rhetorician, that Alexander could not have conquered any countries without an army.

But in cases where the limits of our possible knowledge are very narrow, where the temptation to judge is great, the illusion which presents itself very deceptive, and the evil consequences of error very considerable, the negative element, though it teaches us only how to avoid errors, has even more value than much of that positive instruction which adds to the stock of our knowledge. The restraint which checks our constant inclination to deviate from certain rules, and at last destroys it, is called discipline: It is different from culture, which is intended to form a certain kind of skill, without destroying another kind which is already present. In forming a talent, therefore, which has in itself an impulse to manifest itself, [p. 710] discipline will contribute a negative,1 culture and doctrine a positive, influence.

That our temperament and various talents which like to indulge in free and unchecked exercise (such as imagination and wit) require some kind of discipline, will easily be allowed by everybody. But that reason, whose proper duty it is to prescribe a discipline to all other endeavours, should itself require such discipline, may seem strange indeed. It has in fact escaped that humiliation hitherto, because, considering the solemnity and thorough self-possession in its behaviour, no one has suspected it of thoughtlessly putting imaginations in the place of concepts, and words in the place of things.

In its empirical use reason does not require such criticism, because its principles are constantly subject to the test of experience. Nor is such criticism [p. 711] required in mathematics, where the concepts of reason must at once be represented in concreto in pure intuition, so that everything unfounded and arbitrary is at once discovered. But when neither empirical nor pure intuition keeps reason in a straight groove, that is, when it is used transcendently and according to mere concepts, the discipline to restrain its inclination to go beyond the narrow limits of possible experience, and to keep it from extravagance and error is so necessary, that the whole philosophy of pure reason is really concerned with that one negative discipline only. Single errors may be corrected by censure, and their causes removed by criticism. But when, as in pure reason, we are met by a whole system of illusions and fallacies, well connected among themselves and united by common principles, a separate negative code seems requisite, which, under the name of a discipline, should erect a system of caution and self-examination, founded on the nature of reason and of the objects of its use, before which no false sophistical illusion could stand, but should at once betray itself in spite of all excuses.

It should be well borne in mind, however, [p. 712] that in this second division of the transcendental critique, I mean to direct the discipline of pure reason not to its contents, but only to the method of its knowledge. The former task has been performed in the Elements of Transcendentalism. There is so much similarity in the use of reason, whatever be the subject to which it is applied, and yet, so far as this use is to be transcendental, it is so essentially different from every other, that, without the warning voice of a discipline, especially devised for that purpose, it would be impossible to avoid errors arising necessarily from the improper application of methods, which are suitable to reason in other spheres, only not quite here.

Section I

The Discipline of Pure Reason in its Dogmatical Use

The science of mathematics presents the most brilliant example of how pure reason may successfully enlarge its domain without the aid of experience. Such examples are always contagious, particularly when the faculty is the same, which naturally flatters itself that it will meet with the same success in other cases which it has had in one. Thus pure reason hopes to be able to extend its domain as successfully and as thoroughly [p. 713] in its transcendental as in its mathematical employment; particularly if it there follows the same method which has proved of such decided advantage elsewhere. It is, therefore, of great consequence for us to know whether the method of arriving at apodictic certainty, which in the former science was called mathematical, be identical with that which is to lead us to the same certainty in philosophy, and would have to be called dogmatic.

Philosophical knowledge is that which reason gains from concepts, mathematical, that which it gains from the construction of concepts. By constructing a concept I mean representing a priori the intuition corresponding to it. For the construction of a concept, therefore, a non-empirical intuition is required which, as an intuition, is a single object, but which, nevertheless, as the construction of a concept (of a general representation) must express in the representation something that is generally valid for all possible intuitions which fall under the same concept. Thus I construct a triangle by representing the object corresponding to that concept either by mere imagination, in the pure intuition, or, afterwards on paper also in the empirical intuition, and in both cases entirely a priori without having borrowed the original from any experience. The particular figure drawn on the [p. 714] paper is empirical, but serves nevertheless to express the concept without any detriment to its generality, because, in that empirical intuition, we consider always the act of the construction of the concept only, to which many determinations, as, for instance, the magnitude of the sides and the angles, are quite indifferent, these differences, which do not change the concept of a triangle, being entirely ignored.

Philosophical knowledge, therefore, considers the particular in the general only, mathematical, the general in the particular, nay, even in the individual, all this, however, a priori, and by means of reason; so that, as an individual figure is determined by certain general conditions of construction, the object of the concept, of which this individual figure forms only the schema, must be thought of as universally determined.

The essential difference between these two modes of the knowledge of reason consists, therefore, in the form, and does not depend on any difference in their matter or objects. Those who thought they could distinguish philosophy from mathematics by saying that the former was concerned with quality only, the latter with quantity only, mistook effect for cause. It is owing to the form of mathematical knowledge that it can refer to quanta only, because it is only the concept of quantities that admits of construction, that is, of a priori [p. 715] representation in intuition, while qualities cannot be represented in any but empirical intuition. Hence reason can gain a knowledge of qualities by concepts only. No one can take an intuition corresponding to the concept of reality from anywhere except from experience; we can never lay hold of it a priori by ourselves, and before we have had an empirical consciousness of it. We can form to ourselves an intuition of a cone, from its concept alone, and without any empirical assistance, but the colour of this cone must be given before, in some experience or other. I cannot represent in intuition the concept of a cause in general in any way except by an example supplied by experience, etc. Besides, philosophy treats of quantities quite as much as mathematics; for instance, of totality, infinity, etc., and mathematics treats also of the difference between lines and planes, as spaces of different quality, it treats further of the continuity of extension as one of its qualities. But, though in such cases both have a common object, the manner in which reason treats it is totally different in philosophy and mathematics. The former is concerned with general concepts only, the other can do nothing with the pure concept, but proceeds at once to intuition, in which it looks upon the concept in concreto; yet not in an [p. 716] empirical intuition, but in an intuition which it represents a priori, that is, which it has constructed and in which, whatever follows from the general conditions of the construction, must be valid in general of the object of the constructed concept also.

Let us give to a philosopher the concept of a triangle, and let him find out, in his own way, what relation the sum of its angles bears to a right angle. Nothing is given him but the concept of a figure, enclosed within three straight lines, and with it the concept of as many angles. Now he may ponder on that concept as long as he likes, he will never discover anything new in it. He may analyse the concept of a straight line or of an angle, or of the number three, and render them more clear, but he will never arrive at other qualities which are not contained in those concepts. But now let the geometrician treat the same question. He will begin at once with constructing a triangle. As he knows that two right angles are equal to the sum of all the contiguous angles which proceed from one point in a straight line, he produces one side of his triangle, thus forming two adjacent angles which together are equal to two right angles. He then divides the exterior of these angles by drawing a line parallel with the opposite side of the triangle, and sees that an exterior adjacent angle has been formed, which is equal to an interior, etc. In this way he arrives, through a chain of conclusions, though always guided by intuition, at a thoroughly [p. 717] convincing and general solution of the question.

In mathematics, however, we construct not only quantities (quanta) as in geometry, but also mere quantity (quantitas) as in algebra, where the quality of the object, which has to be thought according to this quantitative concept, is entirely ignored. We then adopt a certain notation for all constructions of quantities (numbers), such as addition, subtraction, extraction of roots, etc., and, after having denoted also the general concept of quantities according to their different relations, we represent in intuition according to general rules, every operation which is produced and modified by quantity. Thus when one quantity is to be divided by another, we place the signs of both together according to the form denoting division, etc., and we thus arrive, by means of a symbolical construction in algebra, quite as well as by an ostensive or geometrical construction of the objects themselves in geometry, at results which our discursive knowledge could never have reached by the aid of mere conceptions.

What may be the cause of this difference between two persons, the philosopher and the mathematician, both practising the art of reason, the former following his path according to concepts, the latter according to intuitions, which he represents a priori according to concepts? If we remember what has been said [p. 718] before in the Elements of Transcendentalism, the cause is clear. We are here concerned not with analytical propositions, which can be produced by a mere analysis of concepts (here the philosopher would no doubt have an advantage over the mathematician), but with synthetical propositions, and synthetical propositions that can be known a priori. We are not intended here to consider what we are really thinking in our concept of the triangle (this would be a mere definition), but we are meant to go beyond that concept, in order to arrive at properties which are not contained in the concept, but nevertheless belong to it. This is impossible, except by our determining our object according to the conditions either of empirical, or of pure intuition. The former would give us an empirical proposition only, through the actual measuring of the three angles. Such a proposition would be without the character of either generality or necessity, and does not, therefore, concern us here at all. The second procedure consists in the mathematical and here the geometrical construction, by means of which I add in a pure intuition, just as I may do in the empirical intuition, everything that belongs to the schema of a triangle in general and, therefore, to its concept, and thus arrive at general synthetical propositions.

I should therefore in vain philosophise, that is, reflect discursively on the triangle, without ever getting beyond the mere definition with which I ought to have begun. There is no doubt a transcendental synthesis, [p. 719] consisting of mere concepts, and in which the philosopher alone can hope to be successful. Such a synthesis, however, never relates to more than a thing in general, and to the conditions under which its perception could be a possible experience. In the mathematical problems, on the contrary, all this, together with the question of existence, does not concern us, but the properties of objects in themselves only (without any reference to their existence), and those properties again so far only as they are connected with their concept.

We have tried by this example to show how great a difference there is between the discursive use of reason, according to concepts, and its intuitive use, through the construction of concepts. The question now arises what can be the cause that makes this twofold use of reason necessary, and how can we discover whether in any given argument the former only, or the latter use also, takes place?

All our knowledge relates, in the end, to possible intuitions, for it is by them alone that an object can be given. A concept a priori (or a non-empirical concept) contains either a pure intuition, in which case it can be constructed, or it contains nothing but the synthesis of possible intuitions, which are not given a priori, and in that case, though we may use it for synthetical [p. 720] and a priori judgments, such judgments can only be discursive, according to concepts, and never intuitive, through the construction of the concept.

There is no intuition a priori except space and time, the mere forms of phenomena. A concept of them, as quanta, can be represented a priori in intuition, that is, can be constructed either at the same time with their quality (figure), or as quantity only (the mere synthesis of the manifold-homogeneous), by means of number. The matter of phenomena, however, by which things are given us in space and time, can be represented in perception only, that is a posteriori. The one concept which a priori represents the empirical contents of phenomena is the concept of a thing in general, and the synthetical knowledge which we may have a priori of a thing in general, can give us nothing but the mere rule of synthesis, to be applied to what perception may present to us a posteriori, but never an a priori intuition of a real object, such an intuition being necessarily empirical.

Synthetical propositions with regard to things in general, the intuition of which does not admit of being given a priori, are called transcendental. Transcendental propositions, therefore, can never be given through a construction of concepts, but only according to concepts a priori. They only contain the rule, according to which we must look empirically for a certain synthetical unity of what cannot be represented in intuition a [p. 721] priori (perceptions). They can never represent any one of their concepts a priori, but can do this only a posteriori, that is, by means of experience, which itself becomes possible according to those synthetical principles only.

If we are to form a synthetical judgment of any concept, we must proceed beyond that concept to the intuition in which it is given. For if we kept within that which is given in the concept, the judgment could only be analytical and an explanation of the concept, in accordance with what we have conceived in it. I may, however, pass from the conception to the pure or empirical intuition which corresponds to it, in order thus to consider it in concreto, and thus to discover what belongs to the object of the concept, whether a priori or a posteriori. The former consists in rational or mathematical knowledge, arrived at by the construction of the concept, the latter in the purely empirical (mechanical) knowledge which can never supply us with necessary and apodictic propositions. Thus I might analyse my empirical concept of gold, without gaining anything beyond being able to enumerate everything that I can really think by this word. This might yield a logical improvement of my knowledge, but no increase or addition. If, however, I take the material which is known by the name of gold, I can make observations on it, and these will yield me different synthetical, but empirical [p. 722] propositions. Again, I might construct the mathematical concept of a triangle, that is, give it a priori in intuition, and gain in this manner a synthetical but rational knowledge of it. But when the transcendental concept of a reality, a substance, a power, etc., is given me, that concept denotes neither an empirical nor a pure intuition, but merely the synthesis of empirical intuitions, which, being empirical, cannot be given a priori. No determining synthetical proposition therefore can spring from it, because the synthesis cannot a priori pass beyond to the intuition that corresponds to it, but only a principle of the synthesis1 of possible empirical intuitions.

A transcendental proposition, therefore, is synthetical knowledge acquired by reason, according to mere concepts; and it is discursive, because through it alone synthetical unity of empirical knowledge becomes possible, while it cannot give us any intuition a priori.

We see, therefore, that reason is used in two [p. 723] ways which, though they share in common the generality of their knowledge and its production a priori, yet diverge considerably afterwards, because in each phenomenon (and no object can be given us, except as a phenomenon), there are two elements, the form of intuition (space and time), which can be known and determined entirely a priori, and the matter (the physical) or the contents, something which exists in space and time, and therefore contains an existence corresponding to sensation. As regards the latter, which can never be given in a definite form except empirically, we can have nothing a priori except indefinite concepts of the synthesis of possible sensations, in so far as they belong to the unity of apperception (in a possible experience). As regards the former, we can determine a priori our concepts in intuition, by creating to ourselves in space and time, through a uniform synthesis, the objects themselves, considering them simply as quanta. The former is called the use of reason according to concepts; and here we can do nothing more than to bring phenomena under concepts, according to their real contents, which therefore can be determined empirically only, that is a posteriori (though in accordance with those concepts as rules of an empirical synthesis). The latter is the use [p. 724] of reason through the construction of concepts, which, as they refer to an intuition a priori, can for that reason be given a priori, and defined in pure intuition, without any empirical data. To consider everything which exists (everything in space or time) whether, and how far, it is a quantum or not; to consider that we must represent in it either existence, or absence of existence; to consider how far this something which fills space or time is a primary substratum, or merely determination of it; to consider again whether its existence is related to something else as cause or effect, or finally, whether it stands isolated or in reciprocal dependence on others, with reference to existence, — this and the possibility, reality, and necessity of its existence, or their opposites, all belong to that knowledge of reason, derived from concepts, which is called philosophical. But to determine a priori an intuition in space (figure), to divide time (duration), or merely to know the general character of the synthesis of one and the same thing in time and space, and the quantity of an intuition in general which arises from it (number), all this is the work of reason by means of the construction of concepts, and is called mathematical.

The great success which attends reason in its mathematical use produces naturally the expectation that it, or rather its method, would have the same success outside the field of quantities also, by reducing all concepts to intuitions which may be given a priori, and by [p. 725] which the whole of nature might be conquered, while pure philosophy, with its discursive concepts a priori, does nothing but bungle in every part of nature, without being able to render the reality of those concepts intuitive a priori, and thereby legitimatised. Nor does there seem to be any lack of confidence on the part of those who are masters in the art of mathematics, or of high expectations on the part of the public at large, as to their ability of achieving success, if only they would try it. For as they have hardly ever philosophised on mathematics (which is indeed no easy task), they never think of the specific difference between the two uses of reason which we have just explained. Current and empirical rules, borrowed from the ordinary operations of reason, are then accepted instead of axioms. From what quarter the concepts of space and time with which alone (as the original quanta) they have to deal, may have come to them, they do not care to enquire, nor do they see any use in investigating the origin of the pure concepts of the understanding, and with it the extent of their validity, being satisfied to use them as they are. In all this no blame would attach to them, if only they did not overstep their proper limits, namely, those of nature. But as it is, they lose themselves, without being aware of it, away from the field of sensibility on the uncertain ground of pure and even transcendental concepts (instabilis tellus, innabilis unda) where they are neither able to stand nor to [p. 726] swim, taking only a few hasty steps, the vestiges of which are soon swept away, while their steps in mathematics become a highway, on which the latest posterity may march on with perfect confidence.

We have chosen it as our duty to determine with accuracy and certainty the limits of pure reason in its transcendental use. These transcendental efforts, however, have this peculiar character that, in spite of the strongest and clearest warnings, they continue to inspire us with new hopes, before the attempt is entirely surrendered at arriving beyond the limits of experience at the charming fields of an intellectual world. It is necessary therefore to cut away the last anchor of that fantastic hope, and to show that the employment of the mathematical method cannot be of the slightest use for this kind of knowledge, unless it be in displaying its own deficiencies; and that the art of measuring and philosophy are two totally different things, though they are mutually useful to each other in natural science, and that the method of the one can never be imitated by the other.

The exactness of mathematics depends on definitions, axioms, and demonstrations. I shall content myself with showing that none of these can be achieved or imitated by the philosopher in the sense in which they are understood by the mathematician. I hope to show at the [p. 727] same time that the art of measuring, or geometry, will by its method produce nothing in philosophy but card-houses, while the philosopher with his method produces in mathematics nothing but vain babble. It is the very essence of philosophy to teach the limits of knowledge, and even the mathematician, unless his talent is limited already by nature and restricted to its proper work, cannot decline the warnings of philosophy or altogether defy them.

I. Of Definitions. To define, as the very name implies, means only to represent the complete concept of a thing within its limits and in its primary character.1 From this point of view, an empirical concept cannot be defined, but can be explained only. For, as we have in an empirical concept some predicates only belonging to a certain class of sensuous objects, we are never certain whether by the word which denotes one and the same object, we do not think at one time a greater, at another a smaller number of predicates. Thus one man may by the [p. 728] concept of gold think, in addition to weight, colour, malleability, the quality of its not rusting, while another may know nothing of the last. We use certain predicates so long only as they are required for distinction. New observations add and remove certain predicates, so that the concept never stands within safe limits. And of what use would it be to define an empirical concept, as for instance that of water, because, when we speak of water and its qualities, we do not care much what is thought by that word, but proceed at once to experiments? the word itself with its few predicates being a designation only and not a concept, so that a so-called definition would be no more than a determination of the word. Secondly, if we reasoned accurately, no a priori given concept can be defined, such as substance, cause, right, equity, etc. For I can never be sure that the clear representation of a given but still confused concept has been completely analysed, unless I know that such representation is adequate to the object. As its concept, however, such as it is given, may contain many obscure representations which we pass by in our analysis, although we use them always in the practical application of the concept, the completeness of the analysis of my concept must always remain doubtful, and can only be rendered probable by means of apt examples, although never apodictically certain. I should [p. 729] therefore prefer to use the term exposition rather than definition, as being more modest, and more likely to be admitted to a certain extent by a critic who reserves his doubts as to its completeness. As therefore it is impossible to define either empirically or a priori given concepts, there remain arbitrary concepts only on which such an experiment may be tried. In such a case I can always define my concept, because I ought certainly to know what I wish to think, the concept being made intentionally by myself, and not given to me either by the nature of the understanding or by experience. But I can never say that I have thus defined a real object. For if the concept depends on empirical conditions, as, for instance, a ship’s chronometer, the object itself and its possibility are not given by this arbitrary concept; it does not even tell us whether there is an object corresponding to it, so that my explanation should be called a declaration (of my project) rather than a definition of an object. Thus there remain no concepts fit for definition except those which contain an arbitrary synthesis that can be constructed a priori. It follows, therefore, that mathematics only can possess definitions, because it is in mathematics alone that we represent a priori in intuition the object which we think, and that object cannot therefore contain either more or less than the concept, because the concept of [p. 730] the object was given by the definition in its primary character, that is, without deriving the definition from anything else. The German language has but the one word Erklärung (literally clearing up) for the terms exposition, explication, declaration, and definition; and we must not therefore be too strict in our demands, when denying to the different kinds of a philosophical clearing up the honourable name of definition. What we really insist on is this, that philosophical definitions are possible only as expositions of given concepts, mathematical definitions as constructions of concepts, originally framed by ourselves, the former therefore analytically (where completeness is never apodictically certain), the latter synthetically. Mathematical definitions make the concept, philosophical definitions explain it only. Hence it follows,

a. That we must not try in philosophy to imitate mathematics by beginning with definitions, except it be by way of experiment. For as they are meant to be an analysis of given concepts, these concepts themselves, although as yet confused only, must come first, and the incomplete exposition must precede the complete one, so that we are able from some characteristics, known to us from an, as yet, incomplete analysis, to infer many things before we come to a complete exposition, that is, the definition of the concept. In philosophy, in fact, the definition [p. 731] in its complete clearness ought to conclude rather than begin our work;1 while in mathematics we really have no concept antecedent to the definition by which the concept itself is first given, so that in mathematics no other beginning is necessary or possible.

b. Mathematical definitions can never be erroneous, because, as the concept is first given by the definition, it contains neither more nor less than what the definition wishes should be conceived by it. But although there can be nothing wrong in it, so far as its contents are concerned, mistakes may sometimes, though rarely, occur in the form or wording, particularly with regard to perfect precision. Thus the common definition of a circle, that it is a curved line, every point of which is equally distant from one and the same point (namely, the centre), is faulty, [p. 732] because the determination of curved is introduced unnecessarily. For there must be a particular theorem, derived from the definition, and easily proved, viz. that every line, all points of which are equidistant from one and the same point, must be curved (no part of it being straight). Analytical definitions, however, may be erroneous in many respects, either by introducing characteristics which do not really exist in the concept, or by lacking that completeness which is essential to a definition, because we can never be quite certain of the completeness of our analysis. It is on these accounts that the method of mathematics cannot be imitated in the definitions of philosophy.

II. Of Axioms. These, so far as they are immediately certain, are synthetical principles a priori. One concept cannot, however, be connected synthetically and yet immediately with another, because, if we wish to go beyond a given concept, a third connecting knowledge is required; and, as philosophy is the knowledge of reason based on concepts, no principle can be found in it deserving the name of an axiom. Mathematics, on the other hand, may well possess axioms, because here, by means of the construction of concepts in the intuition of their object, the predicates may always be connected a priori and immediately; for instance, that three points always lie in a plane. A synthetical principle, on the contrary, made up of concepts only, can never be immediately certain, [p. 733] as, for example, the proposition that everything which happens has its cause. Here I require something else, namely, the condition of the determination by time in a given experience, it being impossible for me to know such a principle, directly and immediately, from the concepts. Discursive principles are, therefore, something quite different from intuitive principles or axioms. The former always require, in addition, a deduction, not at all required for the latter, which, on that very account, are evident, while philosophical principles, whatever their certainty may be, can never pretend to be so. Hence it is very far from true to say that any synthetical proposition of pure and transcendental reason is so evident (as people sometimes emphatically maintain) as the statement that twicetwo are four. It is true that in the Analytic, when giving the table of the principles of the pure understanding, I mentioned also certain axioms of intuition; but the principle there mentioned was itself no axiom, but served only to indicate the principle of the possibility of axioms in general, being itself no more than a principle based on concepts. It was necessary in our transcendental philosophy to show the possibility even of mathematics. Philosophy, therefore, is without axioms, and can never put forward its principles a priori with absolute authority, but must first consent to justify its claims by a thorough deduction. [p. 734]

III. Of Demonstrations. An apodictic proof only, so far as it is intuitive, can be called demonstration. Experience may teach us what is, but never that it cannot be otherwise. Empirical arguments, therefore, cannot produce an apodictic proof. From concepts a priori, however (in discursive knowledge), it is impossible that intuitive certainty, that is, evidence, should ever arise, however apodictically certain the judgment may otherwise seem to be. Demonstrations we get in mathematics only, because here our knowledge is derived not from concepts, but from their construction, that is, from intuition, which can be given a priori, in accordance with the concepts. Even the proceeding of algebra, with its equations, from which by reduction both the correct result and its proof are produced, is a construction by characters, though not geometrical, in which, by means of signs, the concepts, particularly those of the relation of quantities, are represented in intuition, and (without any regard to the heuristic method) all conclusions are secured against errors by submitting each of them to intuitive evidence. Philosophical knowledge cannot claim this advantage, for here we must always consider the general in the abstract (by concepts), while in mathematics we may consider the general in the concrete, in each single intuition, and yet through pure representation a priori, where every mistake becomes at once manifest. I should prefer, [p. 735] therefore, to call the former acroamatic, or audible (discursive) proofs, because they can be carried out by words only (the object in thought), rather than demonstrations, which, as the very term implies, depend on the intuition of the object.

It follows from all this that it is not in accordance with the very nature of philosophy to boast of its dogmatical character, particularly in the field of pure reason, and to deck itself with the titles and ribands of mathematics, an order to which it can never belong, though it may well hope for co-operation with that science. All those attempts are vain pretensions which can never be successful, nay, which can only prove an obstacle in the discovery of the illusions of reason, when ignoring its own limits, and which must mar our success in calling back, by means of a sufficient explanation of our concepts, the conceit of speculation to the more modest and thorough work of self-knowledge. Reason ought not, therefore, in its transcendental endeavours, to look forward with such confidence, as if the path which it has traversed must lead straight to its goal, nor depend with such assurance on its premisses as to consider it unnecessary to look back from time to time, to find out whether, in the progress of its conclusions, errors may come to light, which were overlooked in the principles, and which render it necessary [p. 736] either to determine those principles more accurately or to change them altogether.

I divide all apodictic propositions, whether demonstrable or immediately certain, into Dogmata and Mathemata. A directly synthetical proposition, based on concepts, is a Dogma; a proposition of the same kind, arrived at by the construction of concepts, is a Mathema. Analytical judgments teach us really no more of an object than what the concept which we have of it contains in itself. They cannot enlarge our knowledge beyond the concept, but only clear it. They cannot, therefore, be properly called dogmas (a word which might perhaps best be translated by precepts, Lehrsprüche). According to our ordinary mode of speech, we could apply that name to that class only of the two above-mentioned classes of synthetical propositions a priori which refers to philosophical knowledge, and no one would feel inclined to give the name of Dogma to the propositions of arithmetic or geometry. In this way the usage of language confirms our explanation that those judgments only which are based on conceptions, and not those which are arrived at by the construction of concepts, can be called dogmatic.

Now in the whole domain of pure reason, in its purely speculative use, there does not exist a single directly synthetical judgment based on concepts. We have shown that reason, by means of ideas, is incapable of any synthetical judgments which could claim objective validity, while by means of the concepts of our understanding it establishes no doubt some perfectly certain principles, [p. 737] but not directly from concepts, but indirectly only, by referring such concepts to something purely contingent, namely, possible experience. When such experience (anything as an object of possible experience) is presupposed, these principles are, no doubt, apodictically certain, but in themselves (directly) they cannot even be known a priori. Thus the proposition that everything which happens has its cause, can never be thoroughly understood by means of the concepts alone which are contained in it; hence it is no dogma in itself, although, from another point of view, that is, in the only field of its possible use, namely, in experience, it may be proved apodictically. It should be called, therefore, a principle, and not a precept or a dogma (though it is necessary that it should itself be proved), because it has this peculiarity that it first renders its own proof, namely, experience, possible, and has always to be presupposed for the sake of experience.

If, therefore, there are no dogmata whatever in the speculative use of pure reason, with regard to their contents also, all dogmatical methods, whether borrowed from mathematics or invented on purpose, are alike inappropriate. They only serve to hide mistakes and errors, and thus deceive philosophy, whose true object is to shed the clearest light on every step which reason takes. The method may, however, well be systematical; for our reason (subjectively) is itself a system, though in its [p. 738] pure use, by means of mere concepts, a system intended for investigation only, according to principles of unity, to which experience alone can supply the material. We cannot, however, dwell here on the method of transcendental philosophy, because all we have to do at present is to take stock in order to find out whether we are able to build at all, and how high the edifice may be which we can erect with the materials at our command (the pure concepts a priori).

Section II

The Discipline of Pure Reason in its Polemical Use

Reason in all her undertakings must submit to criticism, and cannot attempt to limit the free exercise of such criticism without injury to herself, and without exposing herself to dangerous suspicion. There is nothing so important with reference to its usefulness, nothing so sacred, that it could withdraw itself from that searching examination which has no respect of persons. The very existence of reason depends on that freedom; for reason can claim no dictatorial authority, but its decrees are rather like the votes of free citizens, every one of whom may freely express, not only his doubts, but even [p. 739] his veto.

But, though reason can never refuse to submit to criticism, it does not follow that she need always be afraid of it, while pure reason in her dogmatical (not mathematical) use is not so thoroughly conscious of having herself obeyed her own supreme laws as not to appear with a certain shyness, nay, without any of her assumed dogmatical authority, before the tribunal of a higher judicial reason.

The case is totally different when reason has to deal, not with the verdicts of a judge, but with the claims of her fellow-citizens, and has to defend itself only against these claims. For as these mean to be as dogmatical in their negations as reason is in her affirmations, reason may justify herself κατ’ ἄνθρωπον, so as to be safe against all damages, and with a good title to her own property that need not fear any foreign claims, although κατ’ ἀλήθειαν it could not itself be established with sufficient evidence.

By the polemical use of pure reason I mean the defence of her own propositions against dogmatical negations. Here the question is not, whether her own assertions may not themselves be false, but it is only to be shown that no one is ever able to prove the opposite with apodictic certainty, nay, even with a higher degree of plausibility. For we are not on sufferance in our possession, [p. 740] when, though our own title may not be sufficient, it is nevertheless quite certain that no one can ever prove its insufficiency.

It is sad, no doubt, and discouraging, that there should be an antithetic of pure reason, and that reason, being the highest tribunal for all conflicts, should be in conflict with herself. We had on a former occasion to treat of such an apparent antithetic, but we saw that it arose from a misunderstanding, phenomena, according to the common prejudice, being taken for things in themselves, and an absolute completeness of their synthesis being demanded in one way or other (being equally impossible in either way), a demand entirely unreasonable with regard to phenomena. There was, therefore, no real contradiction in reason herself when making the two propositions, first, that the series of phenomena given by themselves has an absolutely first beginning; and, secondly, that the series is absolutely and by itself without any beginning; for both propositions are perfectly consistent with each other, because phenomena, with regard to their existence as phenomena, are by themselves nothing, that is, something self-contradictory, so that their hypothesis must naturally lead to contradictory inferences. [p. 741]

We cannot, however, appeal to a similar misunderstanding, in order to remove the conflict of reason, when it is said, for instance, on one side, theistically, that there is a Supreme Being, and on the other, atheistically, that there is no Supreme Being; or if in psychology it is maintained that everything which thinks possesses an absolute and permanent unity and is different, therefore, from all perishable material unity, while others maintain that a soul is not an immaterial unity, and not exempt, therefore from perishableness. For here the object of the question is free from anything heterogeneous or contradictory to its own nature, and our understanding has to deal with things by themselves only and not with phenomena. Here, therefore, we should have a real conflict, if only on the negative side pure reason could advance anything like the ground of an assertion. We may well admit the criticism of the arguments advanced by those who dogmatically assert, without therefore having to surrender these assertions, which are supported at least by the interest of reason, to which the opposite party cannot appeal.

I cannot share the opinion so frequently expressed by excellent and thoughtful men (for instance Sulzer) who, being fully conscious of the weakness of the proofs hitherto advanced, indulge in a hope that the future would supply us with evident demonstrations of the two cardinal propositions of pure reason, namely, that there is a God, and that there is a future life. I am certain, on the [p. 742] contrary, that this will never be the case, for whence should reason take the grounds for such synthetical assertions, which do not refer to objects of experience and their internal possibility? But there is the same apodictic certainty that no man will ever arise to assert the contrary with the smallest plausibility, much less dogmatically. For, as he could prove it by means of pure reason only, he would have to prove that a Supreme Being, and that a thinking subject within us, as pure intelligence, is impossible. But whence will he take the knowledge that would justify him in thus judging synthetically on things far beyond all possible experience? We may, therefore, rest so completely assured that no one will ever really prove the opposite, that there is no need to invent any scholastic arguments. We may safely accept those propositions which agree so well with the speculative interests of our reason in its empirical use, and are besides the only means of reconciling them with our practical interests. As aganst our opponent, who must not be considered here as a critic only, we are always ready with our Non liquet. This must inevitably confound our adversary, while we need not mind his retort, because we can always fall back on the subjective maxim of reason, [p. 743] which our adversary cannot, and can thus, protected by it, look upon all his vain attacks with calmness and indifference.

Thus we see that there is really no antithetic of pure reason, for the only arena for it would be the field of pure theology and psychology, and on that field it is not able to support a champion in full armour and with weapons which we need be afraid of. He can only use ridicule and boasting, and these we may laugh at as mere child’s play. This ought to be a real comfort and inspire reason with new courage; for what else could she depend on, if she herself, who is called upon to remove all errors, were divided against herself, without any hope of peace and quiet possession?

Whatever has been ordained by nature is good for some purpose or other. Even poisons serve to counteract other poisons which are in our own blood, and they must not be absent therefore in a complete collection of medicines. The objections against the vain persuasions and the conceit of our own purely speculative reason are inspired by the very nature of that reason, and must therefore have their own good purpose, which must not be lightly cast aside. Why has Providence placed certain things, which concern our highest interests, so far beyond [p. 744] our reach that we are only able to apprehend them very indistinctly and dubiously, and our enquiring gaze is more excited than satisfied by them? It is very doubtful whether it is useful to venture on any bold answers with regard to such obscure questions, nay, whether it may not be detrimental. But one thing is quite certain, namely, that it is useful to grant to reason the fullest freedom, both of enquiry and of criticism, so that she may consult her own interest without let or hindrance. And this is done quite as much by limiting her insight as by enlarging it, while nothing but mischief must arise from any foreign interference or any attempt to direct reason, against her own natural inclination, towards objects forced upon her from without.

Allow, therefore, your adversary to speak reason, and combat him with weapons of reason only. As to any practical interests you need not be afraid, for in purely speculative discussions they are not involved at all. What comes to light in these discussions is only a certain antinomy of reason which, as it springs from the very nature of reason, must needs be listened to and examined. Rea son is thus improved only by a consideration of both sides of her subject. Her judgment is corrected by the very limitations imposed upon her. What people may differ about is not the matter so much as the tone and manner of these discussions. For, though you have to surrender the language of knowledge, it is perfectly open [p. 745] to you to retain the language of the firmest faith, which need not fear the severest test of reason.

If we could ask that dispassionate philosopher, David Hume, who seemed made to maintain the most perfect equilibrium of judgment, what induced him to undermine by carefully elaborated arguments the persuasion, so useful and so full of comfort for mankind, as that reason is sufficient to assert and to form a definite concept of a Supreme Being, he would answer, Nothing but a wish to advance reason in self-knowledge, and at the same time a certain feeling of indignation at the violence which people wish to inflict on reason by boasting of her powers, and yet at the same time preventing her from openly confessing her weakness of which she has become conscious by her own self-examination. If, on the contrary, you were to ask Priestley, who was guided by the principles of the empirical use of reason only and opposed to all transcendental speculation, what could have induced him to pull down two such pillars of religion as the freedom and immortality of our soul (for the hope of a future life is with him an expectation only of the miracle of a resuscitation), he, who was himself so pious and zealous a teacher of religion, could answer nothing but that he was concerned for reason, which must suffer if certain subjects are withdrawn from the laws of material nature, the only laws which we can accurately know and fix. It [p. 746] would be most unjust to decry the latter, who was able to combine his paradoxical assertions with the interests of religion, and to inflict pain on a well-intentioned man, simply because he could not find his way, the moment he strayed away from the field of natural science. And the same favour must be extended to the equally well-intentioned, and in his moral character quite blameless, Hume, who could not and would not leave his abstract speculations, because he was rightly convinced that their object lies entirely outside the limits of natural science, and within the sphere of pure ideas.

What then is to be done, especially with regard to the danger which is believed to threaten the commonwealth from such speculations? Nothing is more natural, nothing more fair than the decision which you have to come to. Let these people go! If they show talent, if they produce new and profound investigations, in one word, if they show reason, reason can only gain. If you have recourse to anything else but untrammelled reason, if you raise the cry of high treason, and call together the ignorant mob as it were to extinguish a conflagration — you simply render yourself ridiculous. For here the question is not what may be useful or dangerous to the commonwealth, but merely how far reason may advance in her speculations, which are independent of all practical interests; [p. 747] in fact, whether these speculations are to count for anything, or are to be surrendered entirely for practical considerations. Instead of rushing in, sword in hand, it is far wiser to watch the struggle from the safe seat of the critic. That struggle is very hard for the combatants themselves, while to you it need not be anything but entertaining, and, as the issue is sure to be without bloodshed, it may become highly improving to your own intellect. For it is extremely absurd to expect to be enlightened by reason, and yet to prescribe to her beforehand on which side she must incline. Besides, reason is naturally so subdued and checked by reason, that you need not send out patrols in order to bring the civil law to bear on that party whose victory you fear. In this dialectical war no victory is gained that need disturb your peace of mind.

Reason really stands in need of such dialectical strife, and it is much to be wished that it had taken place sooner, and with the unlimited sanction of the public, for, in that case, criticism would sooner have reached complete maturity, and disputes would have come to an end by each party becoming aware of the illusions and prejudices which caused their differences.

There is in human nature a certain disingenuousness which, however, like everything that springs [p. 748] from nature, must contain a useful germ, namely, a tendency to conceal one’s own true sentiments, and to give expression to adopted opinions which are supposed to be good and creditable. There is no doubt that this tendency to conceal oneself and to assume a favourable appearance has helped towards the progress of civilisation, nay, to a certain extent, of morality, because others, who could not see through the varnish of respectability, honesty, and correctness, were led to improve themselves by seeing everywhere these examples of goodness which they believed to be genuine. This tendency, however, to show oneself better than one really is, and to utter sentiments which one does not really share, can only serve provisionally to rescue men from a rude state, and to teach them to assume at least the appearance of what they know to be good. Afterwards, when genuine principles have once been developed and become part of our nature, that disingenuousness must be gradually conquered, because it will otherwise deprave the heart and not allow the good seeds of honest conviction to grow up among the tares of fair appearances.

I am sorry to observe the same disingenuousness, concealment, and hypocrisy even in the utterances of speculative thought, though there are here fewer hindrances in uttering our convictions openly and freely as we ought, and no advantage whatever in our not doing [p. 749] so. For what can be more mischievous to the advancement of knowledge than to communicate even our thoughts in a falsified form, to conceal doubts which we feel in our own assertions, and to impart an appearance of conclusiveness to arguments which we know ourselves to be inconclusive? So long as those tricks arise from personal vanity only (which is commonly the case with speculative arguments, as touching no particular interests, nor easily capable of apodictic certainty) they are mostly counteracted by the vanity of others, with the full approval of the public at large, and thus the result is generally the same as what would or might have been obtained sooner by means of pure ingenuousness and honesty. But where the public has once persuaded itself that certain subtle speculators aim at nothing less than to shake the very foundations of the common welfare of the people, it is supposed to be not only prudent, but even advisable and honourable, to come to the succour of what is called the good cause, by sophistries, rather than to allow to our supposed antagonists the satisfaction of having lowered our tone to that of a purely practical conviction, and having forced us to confess the absence of all speculative and apodictic certainty. I cannot believe this, nor can I admit that the intention of serving a good cause can ever be combined with trickery, misrepresentation, and fraud. That in weighing the arguments of a speculative discussion we ought to be honest, seems the least that [p. 750] can be demanded; and if we could at least depend on this with perfect certainty, the conflict of speculative reason with regard to the important questions of God, the immortality of the soul, and freedom, would long ago have been decided, or would soon be brought to a conclusion. Thus it often happens that the purity of motives and sentiments stands in an inverse ratio to the goodness of the cause, and that its supposed assailants are more honest and more straightforward than its defenders.

Supposing that I am addressing readers who never wish to see a just cause defended by unjust means, I may say that, according to our principles of criticism, and looking not at what commonly happens, but at what in all common fairness ought to happen, there ought to be no polemical use of reason at all. For how can two persons dispute on a subject the reality of which neither of them can present either in real, or even in possible experience, while they brood on the mere idea of it with the sole intention of eliciting something more than the idea, namely, the reality of the object itself? How can they ever arrive at the end of their dispute, as neither of them can make his view comprehensible and certain, or do more than attack and refute the view of his opponent? For this is the fate of all assertions of pure reason. They go beyond the conditions of all possible experience, where no proof [p. 751] of truth is to be found anywhere, but they have to follow, nevertheless, the laws of the understanding, which are intended for empirical use only, but without which no step can be made in synthetical thought. Thus it happens that each side lays open its own weaknesses, and each can avail itself of the weaknesses of the other.

The critique of pure reason may really be looked upon as the true tribunal for all disputes of reason; for it is not concerned in these disputes which refer to objects immediately, but is intended to fix and to determine the rights of reason in general, according to the principles of its original institution.

Without such a critique, reason may be said to be in a state of nature, and unable to establish and defend its assertions and claims except by war. The critique of pure reason, on the contrary, which bases all its decisions on the indisputable principles of its own original institution, secures to us the peace of a legal status, in which disputes are not to be carried on except in the proper form of a lawsuit. In the former state such disputes generally end in both parties claiming victory, which is followed by an uncertain peace, maintained chiefly by the civil power, while in the latter state a sentence is pronounced which, [p. 752] as it goes to the very root of the dispute, must secure an eternal peace. These never-ceasing disputes of a purely dogmatical reason compel people at last to seek for rest and peace in some criticism of reason itself, and in some sort of legislation founded upon such criticism. Thus Hobbes maintains that the state of nature is a state of injustice and violence, and that we must needs leave it and submit ourselves to the constraint of law, which alone limits our freedom in such a way that it may consist with the freedom of others and with the common good.

It is part of that freedom that we should be allowed openly to state our thoughts and our doubts which we cannot solve ourselves, without running the risk of being decried on that account as turbulent and dangerous citizens. This follows from the inherent rights of reason, which recognises no other judge but universal human reason itself. Here everybody has a vote; and, as all improvements of which our state is capable must spring from thence, such rights are sacred and must never be minished. Nay, it would really be foolish to proclaim certain bold assertions, or reckless attacks upon assertions which enjoy the approval of the largest and best portion of the commonwealth, as dangerous; for that would be to impart to them an importance which they do not possess. [p. 753] Whenever I hear that some uncommon genius has demonstrated away the freedom of the human will, the hope of a future life, or the existence of God, I am always desirous to read his book, for I expect that his talent will help me to improve my own insight into these problems. Of one thing I feel quite certain, even without having seen his book, that he has not disproved any single one of these doctrines; not because I imagine that I am myself in possession of irrefragable proofs of them, but because the transcendental critique, by revealing to me the whole apparatus of our pure reason, has completely convinced me that, as reason is insufficient to establish affirmative propositions in this sphere of thought, it is equally, nay, even more powerless to establish the negative on any of these points. For where is this so-called free-thinker to take the knowledge that, for instance, there exists no Supreme Being? This proposition lies outside the field of possible experience and, therefore, outside the limits of all human cognition. The dogmatical defender of the good cause I should not read at all, because I know beforehand that he will attack the sophistries of the other party simply in order to recommend his own. Besides, a mere defence of the common opinion does not supply so much material for new remarks as a strange and ingeniously contrived theory. The opponent of religion, himself dogmatical in his own way, would give me a [p. 754] valuable opportunity for amending here and there the principles of my own critique of pure reason, while I should not be at all afraid of any danger arising from his theories.

But it may be argued that the youth at least, entrusted to our academical teaching, should be warned against such writings, and kept away from a too early knowledge of such dangerous propositions, before their faculty of judgment, or we should rather say, before the doctrines which we wish to inculcate on them, have taken root, and are able to withstand all persuasion and pressure, from whatever quarter it may proceed.

Yes, if the cause of pure reason is always to be pleaded dogmatically, and if opponents are to be disposed of polemically, i.e. simply by taking up arms against them and attacking them by means of proofs of opposite opinions, nothing might seem for the moment more advisable, but nothing would prove in the long run more vain and inefficient than to keep the reason of youth in temporary tutelage, and to guard it against temptation for a time at least. If, however, curiosity or the fashion of the age should afterwards make them acquainted with such writings, will their youthful persuasion then hold good? He who is furnished with dogmatical weapons only in order to resist the attacks of his opponent, and is not able to analyse that hidden dialectic which is concealed in his own breast quite as much as in that of his opponent, sees sophistries which at all events have the charm of [p. 755] novelty, opposed to other sophistries which possess that charm no longer, and excite the suspicion of having imposed on the natural credulity of youth. He sees no better way of showing that he is no longer a child than by ignoring all well-meant warnings, and, accustomed as he is to dogmatism, he swallows the poison which destroys his principles by a new dogmatism.

The very opposite of this is the right course for academical instruction, provided always that it is founded on a thorough training in the principles of the criticism of pure reason. For, in order to practically apply these principles as soon as possible, and to show their sufficiency even when faced by the strongest dialectical illusion, it is absolutely necessary to allow the attacks, which seem so formidable to the dogmatist, to be directed against the young mind whose reason, though weak as yet, has been enlightened by criticism, so as to let him test by its principles the groundless assertions of his opponents one after the other. He cannot find it very difficult to dissolve them all into mere vapour, and thus alone does he early begin to feel his own power and is able to secure himself against all dangerous illusions which in the end lose all their fascination on him. It is true, the same blows which destroy the stronghold [p. 756] of his opponent must prove fatal also to his own speculative structures, if he should wish to erect such. But this need not disturb him, because he does not wish to shelter himself beneath them, but looks out for the fair field of practical philosophy, where he may hope to find firmer ground for erecting his own rational and beneficial system.

There is, therefore, no room for real polemic in the sphere of pure reason. Both parties beat the air and fight with their own shadows, because they go beyond the limits of nature, where there is nothing that they could lay hold of with their dogmatical grasp. They may fight to their hearts’ content, the shadows which they are cleaving grow together again in one moment, like the heroes in Valhalla, in order to disport themselves once more in these bloodless contests.

Nor can we admit a sceptical use of pure reason, which might be called the principle of neutrality in all its disputes. Surely, to stir up reason against itself, to supply it with weapons on both sides, and then to look on quietly and scoffingly while the fierce battle is raging, does not look well from a dogmatical point of view, but has the appearance of a mischievous and malevolent disposition. If, however, we consider the invincible [p. 757] obstinacy and the boasting of the dogmatical sophists, who are deaf to all the warnings of criticism, there really seems nothing left but to meet the boasting on one side by an equally justified boasting on the other, in order at least to startle reason by a display of opposition, and thus to shake her confidence and make her willing to listen to the voice of criticism. But to stop at this point, and to look upon the conviction and confession of ignorance, not only as a remedy against dogmatical conceit, but as the best means of settling the conflict of reason with herself, is a vain attempt that will never give rest and peace to reason. The utmost it can do is to rouse reason from her sweet dogmatical dreams, and to induce her to examine more carefully her own position. As, however, the sceptical manner of avoiding a troublesome business seems to be the shortest way out of all difficulties, and promises to lead to a permanent peace in philosophy, or is chosen at least as the highroad by all who, under the pretence of a scornful dislike of all investigations of this kind, try to give themselves the air of philosophers, it seems necessary to exhibit this mode of thought in its true light.

The Impossibility of a Sceptical Satisfaction of Pure Reason in Conflict with itself [p. 758]

The consciousness of my ignorance (unless we recognise at the same time its necessity) ought, instead of forming the end of my investigations, to serve, on the contrary, as their strongest impulse. All ignorance is either an ignorance of things, or an ignorance of the limits of our cognition. If ignorance is accidental, it should incite us, in the former case, to investigate things dogmatically, in the latter to investigate the limits of possible knowledge critically. That my ignorance is absolutely necessary and that I am absolved from the duty of all further investigation, can never be established empirically by mere observation, but critically only, by a thorough examination of the first sources of our knowledge. The determination of the true limits of our reason, therefore, can be made on a priori grounds only, while its limitation, which consists in a general recognition of our never entirely removable ignorance, may be realised a posteriori also, by seeing how much remains to be known in spite of all that can be known. The former knowledge of our ignorance, possible only by criticism of reason, is truly scientific, the latter is merely matter of experience, [p. 759] where it is never possible to say how far the inferences drawn from it may reach. If I regard the earth, according to the evidence of my senses, as a flat surface, I cannot tell how far it may extend. But what experience teaches me is, that wheresoever I go, I always see before me a space in which I can proceed further. Thus I am conscious of the limits of my actual knowledge of the earth at any given moment, but not of the limits of all possible geography. But if I have got so far as to know that the earth is a sphere and its surface spherical, I am able from any small portion of it, for instance, from a degree, to know definitely and according to principles a priori, the diameter, and through it, the complete periphery of the earth; and, though I am ignorant with regard to the objects which are contained in that surface, I am not so with regard to its extent, its magnitude, and its limits.

In a similar manner the whole of the objects of our knowledge appears to us like a level surface, with its apparent horizon which encircles its whole extent, and was called by us the idea of unconditioned totality. To reach this limit empirically is impossible, and all attempts have proved vain to determine it a priori according to a certain principle. Nevertheless, all questions of pure reason refer to what lies outside of that horizon, or, it may be, on its boundary line. [p. 760]

The celebrated David Hume was one of those geographers of human reason who supposed that all those questions were sufficiently disposed of by being relegated outside that horizon, which, however, he was not able to determine. He was chiefly occupied with the principle of causality, and remarked quite rightly, that the truth of this principle (and even the objective validity of the concept of an efficient cause in general) was based on no knowledge, i.e. on no cognition a priori, and that its authority rested by no means on the necessity of such a law, but merely on its general usefulness in experience, and on a kind of subjective necessity arising from thence, which he called habit. From the inability of reason to employ this principle beyond the limits of experience he inferred the nullity of all the pretensions of reason in her attempts to pass beyond what is empirical.

This procedure of subjecting the facts of reason to examination, and, if necessary, to blame, may be termed the censorship of reason. There can be no doubt that such a censorship must inevitably lead to doubts [p. 761] against all the transcendental employment of such principles. But this is only the second and by no means the last step in our enquiry. The first step in matters of pure reason, which marks its infancy, is dogmatism. The second, which we have just described, is scepticism, and marks the stage of caution on the part of reason, when rendered wiser by experience. But a third step is necessary, that of the maturity and manhood of judgment, based on firm and universally applicable maxims, when not the facts of reason, but reason itself in its whole power and fitness for pure knowledge a priori comes to be examined. This is not the censura merely, but the true criticism of reason, by which not the barrier only, but the fixed frontiers of reason, not ignorance only on this or that point, but ignorance with reference to all possible questions of a certain kind, must be proved from principles, instead of being merely guessed at. Thus scepticism is a resting-place of reason, where it may reflect for a time on its dogmatical wanderings and gain a survey of the region where it happens to be, in order to choose its way with greater certainty for the future: but it can never be its permanent dwelling-place. That can only be found in perfect certainty, whether of our knowledge of the objects themselves or of the limits within which all our knowledge of objects is enclosed. [p. 762]

Our reason is not to be considered as an indefinitely extended plain, the limits of which are known in a general way only, but ought rather to be compared to a sphere the radius of which may be determined from the curvature of the arc of its surface (corresponding to the nature of synthetical propositions a priori), which enables us likewise to fix the extent and periphery of it with perfect certainty. Outside that sphere (the field of experience) nothing can become an object to our reason, nay, questions even on such imaginary objects relate to the subjective principles only for a complete determination of all the relations which may exist between the concepts of the understanding within that sphere.

It is a fact that we are in possession of different kinds of synthetical knowledge a priori, as shown by the principles of the understanding which anticipate experience. If anybody finds it quite impossible to understand the possibility of such principles, he may at first have some doubts as to whether they really dwell within us a priori; but he cannot thus, by the mere powers of the understanding, prove their impossibility, and declare all the steps which reason takes under their guidance as null and void. All he can say is that, if we could understand their origin and genuineness, we should be able to determine the extent and limits of our reason, and that, until that is done, all the [p. 763] assertions of reason are made at random. And in this way a complete scepticism with regard to all dogmatical philosophy, which is not guided by a criticism of reason, is well grounded, though we could not therefore deny to reason such further advance, after the way has once been prepared and secured on firmer ground. For all these concepts, nay, all the questions which pure reason places before us, have their origin, not in experience, but in reason itself, and must therefore be capable of being solved and tested as to their validity or invalidity. Nor are we justified, while pretending that the solution of these problems is really to be found in the nature of things, to decline their consideration and further investigation, under the pretext of our weakness, for reason alone begets all these ideas by itself, and is bound therefore to give an account of their validity or their dialectical vanity.

All sceptical polemic should properly be directed against the dogmatist only who, without any misgivings about his own fundamental objective principles, that is, without criticism, continues his course with undisturbed gravity, and should be intended only to unsettle his brief and to bring him thus to a proper self-knowledge. With regard to what we know or what we cannot know, that polemic is of no consequence whatever. All the unsuccessful dogmatical attempts of reason are facta, and it is always [p. 764] useful to submit them to the censura of the sceptic. But this can decide nothing as to the expectations of reason in her hopes and claims of a better success in future attempts; and no mere censura can put an end to the disputes regarding the rights of human reason.

Hume is, perhaps, the most ingenious of all sceptics, and without doubt the most important with regard to the influence which the sceptical method may exercise in awakening reason to a thorough examination of its rights. It will therefore be worth our while to make clear to ourselves the course of his reasoning and the errors of an intelligent and estimable man, who at the outset of his enquiries was certainly on the right track of truth.

Hume was probably aware, though he never made it quite clear to himself, that in judgments of a certain kind we pass beyond our concept of the object. I have called this class of judgments synthetical. There is no difficulty as to how I may, by means of experience, pass beyond the concept which I have hitherto had. Experience is itself such a synthesis of perceptions through which a concept, which I have by means of one perception, is increased by means of other perceptions. But we imagine that we are able also a priori to pass beyond our concept [p. 765] and thus to enlarge our knowledge. This we attempt to do either by the pure understanding, in relation to that which can at least be an object of experience, or even by means of pure reason, in relation to such qualities of things, or even the existence of such things, as can never occur in experience. Hume in his scepticism did not distinguish between these two kinds of judgments as he ought to have done, but regarded this augmentation of concepts by themselves, and, so to say, the spontaneous generation of our understanding (and of our reason), without being impregnated by experience, as perfectly impossible. Considering all principles a priori as imaginary, he arrived at the conclusion that they were nothing but a habit arising from experience and its laws; that they were therefore merely empirical, that is, in themselves, contingent rules to which we wrongly ascribe necessity and universality. In order to establish this strange proposition, he appealed to the generally admitted principle of the relation between cause and effect. For as no faculty of the understanding could lead us from the concept of a thing to the existence of something else that should follow from it universally and necessarily, he thought himself justified in concluding that, without experience, we have nothing that could augment our concept and give us a right to form a judgment that extends itself a priori. That the light of the sun which shines on the wax should melt the wax and at the same time harden the clay, no understanding, [p. 766] he maintained, could guess from the concepts which we had before of these things, much less infer, according to a law, experience only being able to teach us such a law. We have seen, on the contrary, in the transcendental logic that, though we can never pass immediately beyond the content of a concept that is given us, we are nevertheless able, entirely a priori, but yet in reference to something else, namely, possible experience, to know the law of its connection with other things. If, therefore, wax, which was formerly hard, melts, I can know a priori that something else must have preceded (for instance the heat of the sun) upon which this melting has followed according to a permanent law, although without experience I could never know a priori definitely either from the effect the cause, or from the cause the effect. Hume was therefore wrong in inferring from the mere contingency of our being determined according to the law of causality, the contingency of that law itself, and he mistook our passing beyond the concept of a thing to some possible experience (which is entirely a priori and constitutes the objective reality of it) for the synthesis of the objects of real experience which, no doubt, is always empirical. He thus changed a principle of affinity which resides in the understanding and predicates necessary connection, into a rule of association residing in the imitative faculty of imagination, which can only represent contingent, but [p. 767] never objective connections.

The sceptical errors of that otherwise singularly acute thinker arose chiefly from a defect, which he shared, however, in common with all dogmatists, namely, of not having surveyed systematically all kinds of synthesis a priori of the understanding. For in doing this he would, without mentioning others, have discovered, for instance, the principle of permanency as one which, like causality, anticipates experience. He would thus have been able also to fix definite limits to the understanding in its attempts at expansion a priori and to pure reason. He only narrows the sphere of our understanding, without definitely limiting it, and produces a general mistrust, but no definite knowledge of that ignorance which to us is inevitable. He only subjects certain principles of the understanding to his censura, but does not place the understanding, with reference to all its faculties, on the balance of criticism. He is not satisfied with denying to the understanding what in reality it does not possess, but goes on to deny to it all power of expanding a priori, though he has never really tested all its powers. For this reason, what always defeats scepticism has happened to Hume also, namely, that he himself becomes subject to scepticism, because his objections rest on facts only which are contingent, and not on principles which alone can force a surrender of the right of dogmatical assertion. [p. 768]

As, besides this, he does not sufficiently distinguish between the well-grounded claims of the understanding and the dialectical pretensions of reason, against which, however, his attacks are chiefly directed, it so happens that reason, the peculiar tendency of which has not in the least been destroyed, but only checked, does not at all consider itself shut out from its attempts at expansion, and can never be entirely turned away from them, although it may be punished now and then. Mere attacks only provoke counter attacks, and make us more obstinate in enforcing our own views. But a complete survey of all that is really our own, and the conviction of a certain though a small possession, make us perceive the vanity of higher claims, and induce us, after surrendering all disputes, to live contentedly and peacefully within our own limited, but undisputed domain.

These sceptical attacks are not only dangerous, but even destructive to the uncritical dogmatist who has not measured the sphere of his understanding, and has not, therefore, determined, according to principles, the limits of his own possible knowledge, and does not know beforehand how much he is really able to achieve, but thinks that he is able to find all this out by a purely tentative method. For if he has been found out in one single assertion of his, which he cannot justify, or the fallacy of which he cannot evolve according to principles, [p. 769] suspicion falls on all his assertions, however plausible they may appear.

And thus the sceptic is the true schoolmaster to lead the dogmatic speculator towards a sound criticism of the understanding and of reason. When he has once been brought there, he need fear no further attacks, for he has learnt to distinguish his own possession from that which lies completely beyond it, and on which he can lay no claim, nor become involved in any disputes regarding it. Thus the sceptical method, though it cannot in itself satisfy with regard to the problems of reason, is nevertheless an excellent preparation in order to awaken its circumspection, and to indicate the true means whereby the legitimate possessions of reason may be secured against all attacks.

Section III

The Discipline of Pure Reason with Regard to Hypotheses

As then the criticism of our reason has at last taught us so much at least, that with its pure and speculative use we can arrive at no knowledge at all, would not this seem to open a wide field for hypotheses, as, where we cannot assert with certainty, we are at all events at liberty to form guesses and opinions?

If the faculty of imagination is not simply to [p. 770] indulge in dreams, but to invent and compose under the strict surveillance of reason, it is necessary that there should always be something perfectly certain, and not only invented or resting on opinion, and that is the possibility of the object itself. If that is once given, it is then allowable, so far as its reality is concerned, to have recourse to opinion, which opinion, however, if it is not to be utterly groundless, must be brought in connection with what is really given and therefore certain, as its ground of explanation. In that case, and in that case only, can we speak of an hypothesis.

As we cannot form the least conception of the possibility of a dynamical connection a priori, and as the categories of the pure understanding are not intended to invent any such connection, but only, when it is given in experience, to understand it, we cannot by means of these categories invent one single object as endowed with a new quality not found in experience, or base any permissible hypothesis on such a quality; otherwise we should be supplying our reason with empty chimeras, and not with concepts of things. Thus it is not permissible to invent any new and original powers, as, for instance, an understanding capable of perceiving objects without the aid of the senses; or a force of attraction without any contact; a new kind of substances that should exist, for instance, in space, without being impenetrable, and consequently, also, any connection of substances, different from that which is supplied by experience; [p. 771] no presence, except in space, no duration, except in time. In one word, our reason can only use the conditions of possible experience as the conditions of the possibility of things; it cannot invent them independently, because such concepts, although not self-contradictory, would always be without an object.

The concepts of reason, as was said before, are mere ideas, and it is true that they have no object corresponding to them in experience; but they do not, for all that, refer to purely imaginary objects, which are supposed to be possible. They are purely problematical, in order to supply (as heuristic fictions) regulative principles for the systematical employment of the understanding in the sphere of experience. If they are not that, they would become mere fictions the possibility of which is quite indemonstrable, and which, therefore, can never be employed as hypotheses for the explanation of real phenomena. It is quite permissible to represent the soul to ourselves as simple, in order, according to this idea, to use the complete and necessary unity of all the faculties of the soul, although we cannot understand it in concreto, as the principle of all our enquiries into its internal phenomena. But to assume the soul as a simple substance (which is a transcendent concept) would be a proposition, not only indemonstrable (this is the case with several physical hypotheses), but purely [p. 772] arbitrary and rash: because the simple can never occur in any experience, and if by substance we understand the permanent object of sensuous intuition, the very possibility of a simple phenomenon is perfectly inconceivable. Reason has no right whatever to assume, as an opinion, purely intelligible beings, or purely intelligible qualities of the objects of the senses; although, on the other side, as we have no concepts whatever, either of their possibility or impossibility, we cannot claim any truer insight enabling us to deny dogmatically their possibility.

In order to explain given phenomena, no other things or reasons can be adduced but those which, according to the already known laws of phenomena, have been put in connection with them. A transcendental hypothesis, adducing a mere idea of reason for the explanation of natural things, would therefore be no explanation at all, because it would really be an attempt at explaining what, according to known empirical principles, we do not understand sufficiently by something which we do not understand at all. Nor would the principle of such an hypothesis serve to help the understanding with regard to its objects, but only to satisfy our reason. Order and design in nature must themselves be explained on natural grounds and according to natural laws; and for this [p. 773] purpose even the wildest hypotheses, if only they are physical, are more tolerable than a hyperphysical one, — that is, the appeal to the Divine Author, who is called in for that very purpose. This would be a principle of ratio ignava, to pass by all causes the objective reality of which, in their possibility at least, may be known by continued experience, in order to rest on a mere idea, which no doubt is very agreeable to our reason. With regard to the absolute totality of the ground of explanation in the series of causes, there can be no difficulty, considering that all mundane objects are nothing but phenomena, in which we can never hope to find absolute completeness in the synthesis of the series of conditions.

It is impossible to allow transcendental hypotheses in the speculative use of reason, or the use of hyperphysical instead of physical explanations; partly, because reason is not in the least advanced in that way, but, on the contrary, cut off from its own proper employment, partly because such a licence would in the end deprive reason of all the fruits that spring from the cultivation of its own proper soil, namely, experience. It is true, no doubt, that whenever the explanation of nature seems difficult to us, we should thus always have a transcendent explanation ready to hand, which relieves us of all investigation; but in that case we are led in the end, not to an [p. 774] understanding, but to a complete incomprehensibility of the principle which, from the very beginning, was so designed that it must contain the concept of something which is the absolutely First.

What is, secondly, required in order to render an hypothesis acceptable, is its adequacy for determining a priori, by means of it, all the consequences that are given. If, for that purpose, we have to call in the aid of supplementary hypotheses, they rouse the suspicion of a mere fiction, because each of them requires for itself the same justification as the fundamental idea, and cannot serve therefore as a sufficient witness. No doubt, if we once admit an absolutely perfect cause, there is no difficulty in accounting for all the order, magnitude, and design which are seen in the world. But if we consider what seem to us at least deviations and evils in nature, new hypotheses will be required in order to save the first hypothesis from the objections which it has to encounter. In the same manner, whenever the simple independence of the human soul, which has been admitted in order to account for all its phenomena, is called into question on account of the difficulties arising from phenomena similar to the changes of matter (growth and decay), new hypotheses have to be called in, which may seem plausible, but possess no authority, except what they derive from the opinion [p. 775] which was to yield the chief explanation, and which they themselves were called upon to defend.

If the two hypotheses which we have just mentioned as examples of the assertions of reason (the incorporeal unity of the soul, and the existence of a Supreme Being) are to be accepted, not as hypotheses, but as dogmas proved a priori, we have nothing to say to them. Great care, however, should be taken in that case that they should be proved with the apodictic certainty of a demonstration. It would be as absurd to try to make the reality of such ideas plausible only, as to try to make a geometrical proposition plausible. Reason, independent of all experience, knows everything either a priori, and as necessary, or not at all. Its judgment, therefore, is never opinion, but either an abstaining from all judgments, or apodictic certainty. Opinions and guesses as to what belongs to things can be admitted in explanation only of what is really given, or as resulting, according to empirical laws, from something that is really given. They belong, therefore, to the series of the objects of experience only. Outside that field to opine is the same as to play with thoughts, unless we suppose that even a doubtful and uncertain way of judging might lead us perhaps on to the truth.

But although, when dealing with the purely [p. 776] speculative questions of pure reason, no hypotheses are admissible in order to found on them any propositions, they are perfectly admissible in order, if possible, to defend them; that is to say, they may be used for polemical, but not for dogmatical purposes. Nor do I understand by defending the strengthening of the proofs in support of our assertions, but only the refutation of the dialectical arguments of the opponent which are intended to invalidate our assertions. All synthetical propositions of pure reason have this peculiarity that, although the philosopher who maintains the reality of certain ideas never possesses sufficient knowledge in order to render his own propositions certain, his opponent is equally unable to prove the opposite. It is true, no doubt, that this equality of fortune, which is peculiar to human reason, favours neither of the two parties with regard to their speculative knowledge, and hence the never-ending feuds in this arena. But we shall see nevertheless that, in relation to its practical employment, reason has the right of admitting what, in the sphere of pure speculation, it would not be allowed to admit without sufficient proof. Such admissions, no doubt, detract from the perfection of speculation, but practical interests take no account of this. Here, therefore, reason is in possession, without having to prove the legitimacy of its title, which, indeed, it would be [p. 777] difficult to do. The burden of proof rests, therefore, on the opponent; and as he knows as little of the point in question, to enable him to prove its non-existence, as the other who maintains its reality, it is evident that there is an advantage on the side of him who maintains something as a practically necessary supposition (melior est conditio possidentis). He is clearly entitled, as it were in self-defence, to use the same weapons in support of his own good cause, which the opponent uses against it, that is, to employ hypotheses, which are not intended to strengthen the arguments in favour of his own view, but only to show that the opponent knows far too little of the subject under discussion to flatter himself that he possesses any advantage over us, so far as speculative insight is concerned.

In the field of pure reason, therefore, hypotheses are admitted as weapons of defence only, not in order to establish a right, but simply in order to defend it; and it is our duty at all times to look for a real opponent within ourselves. Speculative reason in its transcendental employment is by its very nature dialectical. The objections which we have to fear lie in ourselves. We must look for them as we look for old, but never superannuated claims, if we wish to destroy them, and thus to establish a permanent peace. External tranquillity is a mere illusion. It is necessary to root up the very germ of these objections which lies in the nature of human reason; and how can we root it up, unless we allow it freedom, nay, [p. 778] offer it nourishment, so that it may send out shoots, and thus discover itself to our eyes, so that we may afterwards destroy it with its very root? Try yourselves therefore to discover objections of which no opponent has ever thought; nay, lend him your weapons, and grant him the most favourable position which he could wish for. You have nothing to fear in all this, but much to hope for, namely, that you may gain a possession which no one will ever again venture to contest.

In order to be completely equipped you require the hypotheses of pure reason also, which, although but leaden weapons (because not steeled by any law of experience), are yet quite as strong as those which any opponent is likely to use against you. If, therefore (for any not speculative reason), you have admitted the immaterial nature of the soul, which is not subject to any corporeal changes, and you are met by the difficulty that nevertheless experience seems to prove both the elevation and the decay of our mental faculties as different modifications of our organs, you can weaken the force of this objection by saying that you look upon the body as a fundamental phenomenon only, which, in our present state (in this life), forms the condition of all the faculties of our sensibility, and hence of our thought. In that case the separation from the body would be the end of the sensuous employment and the beginning of the intelligible employment of our faculty of knowledge. The body would thus have to be [p. 779] considered, not as the cause of our thinking, but only as a restrictive condition of it, and, therefore, if on one side as a support of our sensuous and animal life, on the other, all the more, as an impediment of our pure and spiritual life, so that the dependence of the animal life on the constitution of the body would in no wise prove the dependence of our whole life on the state of our organs. You may go even further and discover new doubts which have either not been raised at all before, or at all events have not been carried far enough.

Generation in the human race, as well as among irrational creatures, depends on so many accidents, on occasion, on sufficient sustenance, on the views and whims of government, nay, even on vice, that it is difficult to believe in the eternal existence of a being whose life has first begun under circumstances so trivial, and so entirely dependent on our own choice. As regards the continuance (here on earth) of the whole race, there is less difficulty, because the accidents in individual cases are subject nevertheless to a rule with regard to the whole. With regard to each individual, however, to expect so important an effect from such insignificant causes seems very strange. But even against this you may adduce the following transcendental hypothesis, namely, that all life is really intelligible only, not subject to the changes of time, and neither [p. 780] beginning in birth, nor ending in death. You may say that this life is phenomenal only, that is, a sensuous representation of the pure spiritual life, and that the whole world of sense is but an image passing before our present mode of knowledge, but, like a dream, without any objective reality in itself; nay, that if we could see ourselves and other objects also as they really are, we should see ourselves in a world of spiritual natures, our community with which did neither begin at our birth nor will end with the death of the body, both being purely phenomenal.

Although it is true that we do not know anything about what we have here been pleading hypothetically against our opponents, and that we ourselves do not even seriously maintain it, it being simply an idea invented for self-defence and not even an idea of reason, yet we are acting throughout quite rationally. In answer to our opponent who imagines that he has exhausted all possibilities, and who wrongly represents the absence of empirical conditions as a proof of the total impossibility of our own belief, we are simply showing him that he can no more, by mere laws of experience, comprehend the whole field of possible things by themselves than we are able, outside of experience, to establish anything for our reason on a really secure foundation. Because we bring forward such hypothetical defences against the pretensions of our boldly denying opponent, we must not be supposed to have [p. 781] adopted these opinions as our own. We abandon them so soon as we have disposed of the dogmatical conceit of our opponent. It seems no doubt very modest and moderate to maintain a simple negative position with regard to the assertions of other people; but to attempt to represent objections as proofs of the opposite opinion is quite as arrogant as to assume the position of the affirming party and its opinions.

It is easy to see, therefore, that in the speculative employment of reason hypotheses are of no value by themselves, but relatively only, as opposed to the transcendental pretensions of the opposite party. For to extend the principles of possible experience to the possibility of things in general is quite as transcendent as to ascribe objective reality to concepts which cannot have an object except outside the limits of all possible experience. The assertory judgments of pure reason must (like everything known by reason) be either necessary or nothing at all. Reason, in fact, knows of no opinions. The hypotheses, however, which we have just been discussing are problematical judgments only, which, at least, cannot be refuted, though they can neither be proved by anything. They are nothing but private1 opinions, but (for our own satisfaction) [p. 782] we cannot well do without them to counteract misgivings that may arise in our minds. In this character they should be maintained, but we must take great care less they should assume independent authority and a certain absolute validity, and drown our reason beneath fictions and phantoms.

Section IV

The Discipline of Pure Reason with Regard to its Proofs

What distinguishes the proofs of transcendental and synthetical propositions from all other proofs of a synthetical knowledge a priori is this, that reason is not allowed here to apply itself directly to an object through its concepts, but has first to prove the objective validity of those concepts and the possibility of their synthesis a priori. This rule is not suggested by prudence only, but refers to the very nature and the possibility of such proofs. If I am to go beyond the concept of an object a priori, this is impossible without some special guidance coming to me from without that concept. In mathematics it is intuition a priori which thus guides my synthesis, so that all our conclusions may be drawn immediately from pure intuition. In transcendental knowledge the same [p. 783] guidance, so long as we are dealing with concepts of the understanding only, is to be found in possible experience. For here the proof does not show that the given concept (for instance, the concept of that which happens) leads directly to another concept (that of a cause). This would be a saltus which nothing could justify. What our proof really shows is, that experience itself and therefore the object of experience would be impossible without such a (causal) connection. The proof, therefore, had at the same time to indicate the possibility of arriving synthetically and a priori at a certain knowledge of things which was not contained in our concept of them. Unless we attend to this point, our proofs, like streams which have broken their banks, run wildly across the fields wherever the inclination of some hidden association may chance to lead them. The semblance of a conviction, based on subjective causes of association and mistaken for the perception of a natural affinity, cannot balance the misgivings which are justly roused by such bold proceedings. Hence all attempts at proving the principle of sufficient reason have, according to the universal admission of all competent judges, been vain; and before the appearance of transcendental criticism it was thought better, as that principle could never be surrendered, to make a sturdy appeal to the common sense of mankind (an expedient which [p. 784] always shows that the cause of reason is desperate) than to attempt new dogmatical proofs of it.

But, if the proposition that has to be proved is an assertion of pure reason, and if I even intend by means of pure ideas to go beyond my empirical concepts, it would be all the more necessary that the proof should contain the justification of such a step of synthesis (if it were possible) as a necessary condition of its own validity. The so-called proof of the simple nature of our thinking substance (soul), derived from the unity of apperception, seems very plausible; but it is confronted by an inevitable difficulty, because, as the absolute unity is not a concept that can be immediately referred to a perception, but, as an idea, can only be inferred, it is difficult to understand how the mere consciousness which is, or at least may be, contained in all thought, though it may be so far a simple representation, can lead me on to the consciousness and the knowledge of a thing, in which thought alone is contained. For if I represent to myself the power of my body, as in motion, it is then to me an absolute unity, and my representation of it is a simple one. I can, therefore, very well express this representation by the motion of a point; because the volume of the body is here of no consequence, and can, without any diminution of its power, be conceived as small as one likes, and, therefore, even as existing in one point. But I should never conclude from this that, if nothing [p. 785] is given to me but the motive power of a body, that body can be conceived as a simple substance, because its representation is independent of the quantity of its volume, and, therefore, simple. I thus detect a paralogism, because the simple in the abstract is totally different from the simple as an object, and the ego which, conceived in the abstract, contains nothing manifold, can, as an object, when signifying the soul, become a very complex concept, comprehending and implying many things. In order to be prepared for such a paralogism (for unless we suspected it, the proof might excite no suspicion), it is absolutely necessary to be always in possession of a criterion of such synthetical propositions, which are meant to prove more than experience can ever supply. This criterion consists in our demanding that the proof should not be carried directly to the predicate in question, but that, first, the principle of the possibility of expanding our given concept a priori into ideas and realising them, should be established. If we always exercised this caution, and, before attempting any such proof, wisely considered ourselves, how, and with what degree of confidence, we might expect such an expansion through pure reason, and whence we might take, in such cases, knowledge which cannot be evolved from concepts nor anticipated with reference [p. 786] to possible experience, we might spare ourselves many difficult, and yet fruitless endeavours, by not asking of reason what evidently is beyond its power, or rather, by subjecting reason, which when once under the influence of this passion for speculative conquest, is not easily checked, to a thorough discipline of moderation.

The first rule, therefore, is to attempt no transcendental proofs before having first considered from whence we should take the principles on which such proofs are to be based, and by what right we may expect our conclusions to be successful. If they are principles of the understanding (for instance of causality), it is useless to attempt to arrive, by means of them, at ideas of pure reason; because they are valid only with regard to objects of experience. If they are principles of pure reason, it is again labour lost, because, though reason possesses such principles, they are all, as objective principles, dialectical and cannot be valid, except perhaps as regulative principles, for the empirical use of reason, in order to make it systematically coherent. If such so-called proofs exist already, we ought to meet their deceptive pleadings with the non liquet of a mature judgment; and although we may be unable to expose their sophisms, we have a perfect right [p. 787] to demand a deduction of the principles employed, which, if these principles are to have their origin in reason alone, will never be forthcoming. You may thus dispense with the analysis and refutation of every one of these sophisms, and dispose in a lump of the endless fallacies of Dialectic, by appealing to the tribunal of critical reason, which insists on laws.

The second peculiarity of transcendental proofs is this, that for every transcendental proposition one proof only can be found. If I have to draw conclusions, not from concepts, but from the intuition which corresponds to a concept, whether it be pure intuition, as in mathematics, or empirical, as in physical science, the intuition on which my conclusions are to rest supplies me with manifold material for synthetical propositions, which I may connect in more than one way, so that, by starting from different points, I can arrive at the same conclusion by different paths.

Every transcendental proposition, on the contrary, starts from one concept only, and predicates the synthetical condition of the possibility of the object, according to that concept. There can therefore be but one proof, because beside that concept there is nothing else whereby that object could be determined. The proof therefore [p. 788] can contain nothing more but the determination of an object in general according to that concept, which is itself one only. In the transcendental Analytic, for instance, we had deduced the principle, that everything which happens has a cause, from the single condition of the objective possibility of the concept of an event in general, namely, that the determination of any event in time, and therefore the event itself also, as belonging to experience, would be impossible, unless it were subject to such a dynamical rule. This is therefore the only possible proof; for the event which we represent to ourselves has objective validity, that is, truth, on this condition only, that an object is determined as belonging to that concept by means of the law of causality. It is true that other arguments in support of this proposition have been attempted, for instance, one derived from contingency; but if that argument is examined more carefully, we can discover no characteristic sign of contingency, except the happening, that is, existence preceded by the non-existence of the object, which leads us back to the same argument as before. If the proposition has to be proved that everything which thinks is simple, no attention is paid to what is manifold in thought, and the concept of the ego only is kept in view, which is simple, and to which all thinking is referred. The same applies to the transcendental proof of the existence of God, which rests entirely on the reciprocability of the two concepts of a most real [p. 789] and a necessary Being, and cannot be found anywhere else.

By this caution the criticism of the assertions of reason is much simplified. Wherever reason operates with concepts only, only one proof is possible, if any. If therefore we see the dogmatist advance with his ten proofs, we may be sure that he has none. For if he had one which (as it ought to be in all matters of pure reason) had apodictic power, what need would he have of others? His object can only be the same as that of the parliamentary lawyer who has one argument for one person, and another for another. He wants to take advantage of the weakness of the judges, who, without enquiring more deeply, and in order to get away as soon as possible, lay hold of the first argument that catches their attention, and decide accordingly.

The third peculiar rule of pure reason, if it is once subjected to a proper discipline with regard to transcendental proofs, is this, that such proofs must never be apagogical or circumstantial, but always ostensive or direct. The direct or ostensive proof combines, with regard to every kind of knowledge, a conviction of its truth with an insight into its sources; the apagogical proof, on the contrary, though it may produce certainty, cannot help us to comprehend the truth in its connection with the grounds of its possibility. It is therefore a mere expedient, [p. 790] and cannot satisfy all the requirements of reason. The apagogical proofs have, however, this advantage with regard to their evidence over direct proofs, that contradiction always carries with it more clearness in the representation than the best combination, and thus approaches more to the intuitional character of a demonstration.

The real reason why apagogical proofs are so much employed in different sciences, seems to be this. If the grounds from which some knowledge is to be derived are too numerous or too deeply hidden, one tries whether they may not be reached through their consequences. Now it is quite true that this modus ponens, that is, this inferring of the truth of some knowledge from the truth of its consequences, is only permitted, if all possible consequences flowing from it are true. In that case they have only one possible ground, which therefore is also the true one. This procedure, however, is impracticable, because to discover all possible consequences of any given proposition exceeds our powers. Nevertheless, this mode of arguing is employed, though under a certain indulgence, whenever something is to be established as a hypothesis only, in which case a conclusion, according to analogy, is admitted, namely, that if as many consequences as one has tested agree with an assumed ground, all others will also agree with it. To change in this way a hypothesis into a demonstrated truth, is clearly impossible. [p. 791] The modus tollens of reasoning, from consequences to their grounds, is not only perfectly strict, but also extremely easy. For if one single false consequence only can be drawn from a proposition, that proposition is wrong. Instead, therefore, of examining, for the sake of an ostensive proof, the whole series of grounds that may lead us to the truth of a cognition by means of a perfect insight into its possibility, we have only to prove that one single consequence, resulting from the opposite, is false, in order to show that the opposite itself is false, and therefore the cognition, which we had to prove, true.

This apagogical method of proof, however, is admissible in those sciences only where it is impossible to foist the subjective elements of our representations into the place of what is objective, namely, the knowledge of that which exists in the object. When this is not impossible, it must often happen that the opposite of any proposition contradicts the subjective conditions of thought only, but not the object itself, or, that both propositions contradict each other under a subjective condition, which is mistaken as objective, so that, as the condition is false, both may be false, without our being justified in inferring the truth of the one from the falseness of the other.

In mathematics such subreptions are impossible; [p. 792] and it is true, therefore, that the apagogical proof has its true place there. In natural science, in which everything is based on empirical intuitions, that kind of subreption can generally be guarded against by a repeated comparison of observations; but even thus, this mode of proof is of little value there. The transcendental endeavours of pure reason, however, are all made within the very sphere of dialectical illusion, where what is subjective presents itself, nay, forces itself upon reason in its premisses as objective. Here, therefore, it can never be allowed, with reference to synthetical propositions, to justify one’s assertions by refuting their opposite. For, either this refutation may be nothing but the mere representation of the conflict of the opposite opinion with the subjective conditions under which our reason could alone comprehend it, and this would be of no avail for rejecting the proposition itself, — (thus we see, for instance, that the unconditioned necessity of the existence of a Being cannot possibly be comprehended by us, which subjectively bars every speculative proof of a necessary Supreme Being but by no means, the possibility of such a Being by itself), — or, on the other hand, it may be that both the affirmative and the negative party have been deceived by the transcendental illusion, and base their arguments on an impossible concept of an object. In that case the rule applies, non entis nulla sunt praedicata, that is, [p. 793] everything that has been asserted with regard to an object, whether affirmatively or negatively, is wrong, and we cannot therefore arrive apagogically at the knowledge of truth by the refutation of its opposite. If, for example, we assume that the world of sense is given by itself in its totality, it is wrong to conclude that it must be either infinite in space, or finite and limited; for either is wrong, because phenomena (as mere representations) which nevertheless are to be things by themselves (as objects) are something impossible, and the infinitude of this imaginary whole, though it might be unconditioned, would (because everything in phenomena is conditioned) contradict that very unconditioned quantity which is presupposed in its concept.

The apagogical mode of proof is also the blind by which the admirers of our dogmatical philosophy have always been deceived. It may be compared to a prizefighter who is willing to prove the honour and the incontestable rights of his adopted party by offering battle to all and every one who should dare to doubt them. Such brawling, however, settles nothing, but only shows the respective strength of the two parties, and even this on the part of those only who take the offensive. The spectators, seeing that each party is alternately conqueror and conquered, [p. 794] are often led to regard the very object of the dispute with a certain amount of scepticism. In this, however, they are wrong, and it is sufficient to remind them of non defensoribus istis tempus eget. It is absolutely necessary that every one should plead his cause directly by means of a legitimate proof based on a transcendental deduction of the grounds of proof. Thus only can we see what he may have to say himself in favour of his own claims of reason. If his opponent relies on subjective grounds only, it is easy, no doubt, to refute him; but this does not benefit the dogmatist, who generally depends quite as much on the subjective grounds of his judgment, and can be quite as easily driven into a corner by his opponent. If, on the contrary, both parties employ only the direct mode of proof, they will either themselves perceive the difficulty, nay, the impossibility of finding any title for their assertions, and appeal in the end to prescription only, or, our criticism will easily discover the dogmatical illusion, and compel pure reason to surrender its exaggerated pretensions in the sphere of speculative thought, and to retreat within the limits of its own domain, — that of practical principles.

[1 ]I am well aware that in the language of the schools, discipline is used as synonymous with instruction. But there are so many cases in which the former term, in the sense of restraint, is carefully distinguished from the latter in the sense of teaching, and the nature of things makes it so desirable to preserve the only suitable expressions for that distinction, that I hope that the former term may never be allowed to be used in any but a negative meaning.

[1 ]In the concept of cause I really pass beyond the empirical concept of an event, but not to the intuition which represents the concept of cause in concreto, but to the conditions of time in general, which in experience might be found in accordance with the concept of cause. I therefore proceed here, according to concepts only, but cannot proceed by means of the construction of concepts, because the concept is only a rule for the synthesis of perceptions, which are not pure intuitions, and therefore cannot be given a priori.

[1 ]Completeness means clearness and sufficiency of predicates; limits mean precision, no more predicates being given than belong to the complete concept; in its primary character means that the determination of these limits is not derived from anything else, and therefore in need of any proof, because this would render the so-called definition incapable of standing at the head of all the judgments regarding its object.

[1 ]Philosophy swarms with faulty definitions, particularly such as contain some true elements of a definition, but not all. If, therefore, it were impossible to use a concept until it had been completely defined, philosophy would fare very ill. As, however, we may use a definition with perfect safety, so far at least as the elements of the analysis will carry us, imperfect definitions also, that is, propositions which are not yet properly definitions, but are yet true, and, therefore, approximations to a definition, may be used with great advantage. In mathematics definitions belong ad esse, in philosophy ad melius esse. It is desirable, but it is extremely difficult to construct a proper definition. Jurists are without a definition of right to the present day.

[1 ]Read reine instead of keine.