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

SUPPLEMENT II

Preface to the Second Edition. 1787. [p. vii]

Whether the treatment of that class of knowledge with which reason is occupied follows the secure method of a science or not, can easily be determined by the result. If, after repeated preparations, it comes to a standstill, as soon as its real goal is approached, or is obliged, in order to reach it, to retrace its steps again and again, and strike into fresh paths; again, if it is impossible to produce unanimity among those who are engaged in the same work, as to the manner in which their common object should be obtained, we may be convinced that such a study is far from having attained to the secure method of a science, but is groping only in the dark. In that case we are conferring a great benefit on reason, if we only find out the right method, though many things should have to be surrendered as useless, which were comprehended in the original aim that had been chosen without sufficient reflection.

That Logic, from the earliest times, has followed that [p. viii] secure method, may be seen from the fact that since Aristotle it has not had to retrace a single step, unless we choose to consider as improvements the removal of some unnecessary subtleties, or the clearer definition of its matter, both of which refer to the elegance rather than to the solidity of the science. It is remarkable also, that to the present day, it has not been able to make one step in advance, so that, to all appearance, it may be considered as completed and perfect. If some modern philosophers thought to enlarge it, by introducing psychological chapters on the different faculties of knowledge (faculty of imagination, wit, etc.), or metaphysical chapters on the origin of knowledge, or the different degrees of certainty according to the difference of objects (idealism, scepticism, etc.), or lastly, anthropological chapters on prejudices, their causes and remedies, this could only arise from their ignorance of the peculiar nature of logical science. We do not enlarge, but we only disfigure the sciences, if we allow their respective limits to be confounded: and the limits of logic are definitely fixed by the fact, that it is a science which has nothing to do but fully to exhibit and strictly to prove all formal [p. ix] rules of thought (whether it be a priori or empirical, whatever be its origin or its object, and whatever be the impediments, accidental or natural, which it has to encounter in the human mind).

That logic should in this respect have been so successful, is due entirely to its limitation, whereby it has not only the right, but the duty, to make abstraction of all the objects of knowledge and their differences, so that the understanding has to deal with nothing beyond itself and its own forms. It was, of course, far more difficult for reason to enter on the secure method of science, when it has to deal not with itself only, but also with objects. Logic, therefore, as a kind of preparation (propaedeutic) forms, as it were, the vestibule of the sciences only, and where real knowledge is concerned, is presupposed for critical purposes only, while the acquisition of knowledge must be sought for in the sciences themselves, properly and objectively so called.

If there is to be in those sciences an element of reason, something in them must be known a priori, and knowledge may stand in a twofold relation to its object, by either simply determining [p. x] it and its concept (which must be supplied from elsewhere), or by making it real also. The former is theoretical, the latter practical knowledge of reason. In both the pure part, namely, that in which reason determines its object entirely a priori (whether it contain much or little), must be treated first, without mixing up with it what comes from other sources; for it is bad economy to spend blindly whatever comes in, and not to be able to determine, when there is a stoppage, which part of the income can bear the expenditure, and where reductions must be made.

Mathematics and physics are the two theoretical sciences of reason, which have to determine their objects a priori; the former quite purely, the latter partially so, and partially from other sources of knowledge besides reason.

Mathematics, from the earliest times to which the history of human reason can reach, has followed, among that wonderful people of the Greeks, the safe way of a science. But it must not be supposed that it was as easy for mathematics as for logic, in which reason is concerned with itself alone, to find, or rather to make for itself that royal road. I believe, on the contrary, that there was a long period of tentative work (chiefly [p. xi] still among the Egyptians), and that the change is to be ascribed to a revolution, produced by the happy thought of a single man, whose experiment pointed unmistakably to the path that had to be followed, and opened and traced out for the most distant times the safe way of a science. The history of that intellectual revolution, which was far more important than the discovery of the passage round the celebrated Cape of Good Hope, and the name of its fortunate author, have not been preserved to us. But the story preserved by Diogenes Laertius, who names the reputed author of the smallest elements of ordinary geometrical demonstration, even of such as, according to general opinion, do not require to be proved, shows, at all events, that the memory of the revolution, produced by the very first traces of the discovery of a new method, appeared extremely important to the mathematicians, and thus remained unforgotten. A new light flashed on the first man who demonstrated the properties of the isosceles triangle1 (whether his name was Thales or any other name), for he found that he had not to investigate what [p. xii] he saw in the figure, or the mere concept of that figure, and thus to learn its properties; but that he had to produce (by construction) what he had himself, according to concepts a priori, placed into that figure and represented in it, so that, in order to know anything with certainty a priori, he must not attribute to that figure anything beyond what necessarily follows from what he has himself placed into it, in accordance with the concept.

It took a much longer time before physics entered on the high way of science: for no more than a century and a half has elapsed, since Bacon’s ingenious proposal partly initiated that discovery, partly, as others were already on the right track, gave a new impetus to it, — a discovery which, like the former, can only be explained by a rapid intellectual revolution. In what I have to say, I shall confine myself to natural science, so far as it is founded on empirical principles.

When Galilei let balls of a particular weight, which he had determined himself, roll down an inclined plain, or Torricelli made the air carry a weight, which he had previously determined to be equal to that of a definite volume of water; or when, in later times, Stahl1 changed metal into lime, and lime again into metals, by withdrawing and restoring something, a new [p. xiii] light flashed on all students of nature. They comprehended that reason has insight into that only, which she herself produces on her own plan, and that she must move forward with the principles of her judgments, according to fixed law, and compel nature to answer her questions, but not let herself be led by nature, as it were in leading strings, because otherwise accidental observations, made on no previously fixed plan, will never converge towards a necessary law, which is the only thing that reason seeks and requires. Reason, holding in one hand its principles, according to which concordant phenomena alone can be admitted as laws of nature, and in the other hand the experiment, which it has devised according to those principles, must approach nature, in order to be taught by it: but not in the character of a pupil, who agrees to everything the master likes, but as an appointed judge, who compels the witnesses to answer the questions which he himself proposes. Therefore even the science of physics entirely owes the beneficial revolution in its character to the happy thought, that we ought to seek in nature (and not [p. xiv] import into it by means of fiction) whatever reason must learn from nature, and could not know by itself, and that we must do this in accordance with what reason itself has originally placed into nature. Thus only has the study of nature entered on the secure method of a science, after having for many centuries done nothing but grope in the dark.

Metaphysic, a completely isolated and speculative science of reason, which declines all teaching of experience, and rests on concepts only (not on their application to intuition, as mathematics), in which reason therefore is meant to be her own pupil, has hitherto not been so fortunate as to enter on the secure path of a science, although it is older than all other sciences, and would remain, even if all the rest were swallowed up in the abyss of an all-destroying barbarism. In metaphysic, reason, even if it tries only to understand a priori (as it pretends to do) those laws which are confirmed by the commonest experience, is constantly brought to a standstill, and we are obliged again and again to retrace our steps, because they do not lead us where we want to go; while as to any unanimity among those who are engaged [p. xv] in the same work, there is so little of it in metaphysic, that it has rather become an arena, specially destined, it would seem, for those who wish to exercise themselves in mock fights, and where no combatant has, as yet, succeeded in gaining an inch of ground that he could call permanently his own. It cannot be denied, therefore, that the method of metaphysic has hitherto consisted in groping only, and, what is the worst, in groping among mere concepts.

What then can be the cause that hitherto no secure method of science has been discovered? Shall we say that it is impossible? Then why should nature have visited our reason with restless aspiration to look for it, as if it were its most important concern? Nay more, how little should we be justified in trusting our reason if, with regard to one of the most important objects we wish to know, it not only abandons us, but lures us on by vain hopes, and in the end betrays us! Or, if hitherto we have only failed to meet with the right path, what indications are there to make us hope that, if we renew our researches, we shall be more successful than others before us?

The examples of mathematics and natural science, which by one revolution have become what they now are, seem [p. xvi] to me sufficiently remarkable to induce us to consider, what may have been the essential element in that intellectual revolution which has proved so beneficial to them, and to make the experiment, at least, so far as the analogy between them, as sciences of reason, with metaphysic allows it, of imitating them. Hitherto it has been supposed that all our knowledge must conform to the objects: but, under that supposition, all attempts to establish anything about them a priori, by means of concepts, and thus to enlarge our knowledge, have come to nothing. The experiment therefore ought to be made, whether we should not succeed better with the problems of metaphysic, by assuming that the objects must conform to our mode of cognition, for this would better agree with the demanded possibility of an a priori knowledge of them, which is to settle something about objects, before they are given us. We have here the same case as with the first thought of Copernicus, who, not being able to get on in the explanation of the movements of the heavenly bodies, as long as he assumed that all the stars turned round the spectator, tried, whether he could not succeed better, by assuming the spectator to be turning round, and the stars to be at rest. A similar experiment may be tried in metaphysic, so far as the intuition of objects is [p. xvii] concerned. If the intuition had to conform to the constitution of objects, I do not see how we could know anything of it a priori; but if the object (as an object of the senses) conforms to the constitution of our faculty of intuition, I can very well conceive such a possibility. As, however, I cannot rest in these intuitions, if they are to become knowledge, but have to refer them, as representations, to something as their object, and must determine that object by them, I have the choice of admitting, either that the concepts, by which I carry out that determination, conform to the object, being then again in the same perplexity on account of the manner how I can know anything about it a priori; or that the objects, or what is the same, the experience in which alone they are known (as given objects), must conform to those concepts. In the latter case, the solution becomes more easy, because experience, as a kind of knowledge, requires understanding, and I must therefore, even before objects are given to me, presuppose the rules of the understanding as existing within me a priori, these rules being expressed in concepts a priori, to which all objects of experience must necessarily conform, and with which they must agree. With regard to objects, [p. xviii] so far as they are conceived by reason only, and conceived as necessary, and which can never be given in experience, at least in that form in which they are conceived by reason, we shall find that the attempts at conceiving them (for they must admit of being conceived) will furnish afterwards an excellent test of our new method of thought, according to which we do not know of things anything a priori except what we ourselves put into them.1

This experiment succeeds as well as we could desire, and promises to metaphysic, in its first part, which deals with concepts a priori, of which the corresponding objects may be given in experience, the secure method of a science. For by [p. xix] thus changing our point of view, the possibility of knowledge a priori can well be explained, and, what is still more, the laws which a priori lie at the foundation of nature, as the sum total of the objects of experience, may be supplied with satisfactory proofs, neither of which was possible with the procedure hitherto adopted. But there arises from this deduction of our faculty of knowing a priori, as given in the first part of metaphysic, a somewhat startling result, apparently most detrimental to the objects of metaphysic that have to be treated in the second part, namely, the impossibility of going with it beyond the frontier of possible experience, which is precisely the most essential purpose [p. xx] of metaphysical science. But here we have exactly the experiment which, by disproving the opposite, establishes the truth of our first estimate of the knowledge of reason a priori, namely, that it can refer to phenomena only, but must leave the thing by itself as unknown to us, though as existing by itself. For that which impels us by necessity to go beyond the limits of experience and of all phenomena, is the unconditioned, which reason postulates in all things by themselves, by necessity and by right, for everything conditioned, so that the series of conditions should thus become complete. If then we find that, under the supposition of our experience conforming to the objects as things by themselves, it is impossible to conceive the unconditioned without contradiction, while, under the supposition of our representation of things, as they are given to us, not conforming to them as things by themselves, but, on the contrary, of the objects conforming to our mode of representation, that contradiction vanishes, and that therefore the unconditioned must not be looked for in things, so far as we know them (so far as they are given to us), but only so far as we do not know them (as things by themselves), we clearly perceive that, what we at first assumed tentatively only, is fully confirmed.1 But, after all [p. xxi] progress in the field of the supersensuous has thus been denied to speculative reason, it is still open to us to see, whether in the practical knowledge of reason data may not be found which enable us to determine that transcendent concept of the unconditioned which is demanded by reason, in order thus, according to the wish of metaphysic, to get beyond the limits of all possible experience, by means of our knowledge a priori, which is possible to us for practical purposes only. In this case, speculative reason has at least gained for us room for such an extension of knowledge, though it had to leave it empty, so that we are not only at liberty, but are really called upon to fill it up, if we are able, by practical data of reason.1 [p. xxii]

The very object of the critique of pure speculative reason consists in this attempt at changing the old procedure of metaphysic, and imparting to it the secure method of a science, after having completely revolutionised it, following the example of geometry and physical science. That critique is a treatise on the method (Traité de la méthode), not a system of the science itself; but it marks out nevertheless the whole plan of that science, both with regard to its limits, and to its internal organisation. For pure speculative reason has this peculiar [p. xxiii] advantage that it is able, nay, bound to measure its own powers, according to the different ways in which it chooses its own objects, and to completely enumerate the different ways of choosing problems; thus tracing a complete outline of a system of metaphysic. This is due to the fact that, with regard to the first point, nothing can be attributed to objects in knowledge a priori, except what the thinking subject takes from within itself; while, with regard to the second point, reason, so far as its principles of cognition are concerned, forms a separate and independent unity, in which, as in an organic body, every member exists for the sake of all others, and all others exist for the sake of the one, so that no principle can be safely applied in one relation, unless it has been carefully examined in all its relations, to the whole employment of pure reason. Hence, too, metaphysic has this singular advantage, an advantage which cannot be shared by any other science, in which reason has to deal with objects (for Logic deals only with the form of thought in general) that, if it has once attained, by means of this critique, to the secure method of a science, it can completely comprehend the whole field of knowledge [p. xxiv] pertaining to it, and thus finish its work and leave it to posterity, as a capital that can never be added to, because it has only to deal with principles and the limits of their employment, which are fixed by those principles themselves. And this completeness becomes indeed an obligation, if it is to be a fundamental science, of which we must be able to say, ‘nil actum reputans, si quid superesset agendum.’

But it will be asked, what kind of treasure is it which we mean to bequeath to posterity in this metaphysic of ours, after it has been purified by criticism, and thereby brought to a permanent condition? After a superficial view of this work, it may seem that its advantage is negative only, warning us against venturing with speculative reason beyond the limits of experience. Such is no doubt its primary use: but it becomes positive, when we perceive that the principles with which speculative reason ventures beyond its limits, lead inevitably, not to an extension, but, if carefully considered, to a narrowing of the employment of reason, because, by indefinitely extending the limits of sensibility, to which [p. xxv] they properly belong, they threaten entirely to supplant the pure (practical) employment of reason. Hence our critique, by limiting sensibility to its proper sphere, is no doubt negative; but by thus removing an impediment, which threatened to narrow, or even entirely to destroy its practical employment, it is in reality of positive, and of very important use, if only we are convinced that there is an absolutely necessary practical use of pure reason (the moral use), in which reason must inevitably go beyond the limits of sensibility, and though not requiring for this purpose the assistance of speculative reason, must at all events be assured against its opposition, lest it be brought in conflict with itself. To deny that this service, which is rendered by criticism, is a positive advantage, would be the same as to deny that the police confers upon us any positive advantage, its principal occupation being to prevent violence, which citizens have to apprehend from citizens, so that each may pursue his vocation in peace and security. We had established in the analytical part of our critique the following points: — First, that space and time are only forms of sensuous intuition, therefore conditions of the existence of things, as phenomena only; Secondly, that we have no concepts of the understanding, and therefore nothing whereby we can arrive at the knowledge of things, except in so far as an intuition [p. xxvi] corresponding to these concepts can be given, and consequently that we cannot have knowledge of any object, as a thing by itself, but only in so far as it is an object of sensuous intuition, that is, a phenomenon. This proves no doubt that all speculative knowledge of reason is limited to objects of experience; but it should be carefully borne in mind, that this leaves it perfectly open to us, to think the same objects as things by themselves, though we cannot know them.1 For otherwise we should arrive at the absurd conclusion, that there is phenomenal appearance without [p. xxvii] something that appears. Let us suppose that the necessary distinction, established in our critique, between things as objects of experience and the same things by themselves, had not been made. In that case, the principle of causality, and with it the mechanism of nature, as determined by it, would apply to all things in general, as efficient causes. I should then not be able to say of one and the same being, for instance the human soul, that its will is free, and, at the same time, subject to the necessity of nature, that is, not free, without involving myself in a palpable contradiction: and this because I had taken the soul, in both propositions, in one and the same sense, namely, as a thing in general (as something by itself), as, without previous criticism, I could not but take it. If, however, our criticism was true, in teaching us to take an object in two senses, namely, either as a phenomenon, or as a thing by itself, and if the deduction of our concepts of the understanding was correct, and the principle of causality applies to things only, if taken in the first sense, namely, so far as they are objects of experience, but not to things, if taken in their second sense, we can, without any contradiction, think the same will when phenomenal (in visible actions) as necessarily [p. xxviii] conforming to the law of nature, and so far, not free, and yet, on the other hand, when belonging to a thing by itself, as not subject to that law of nature, and therefore free. Now it is quite true that I may not know my soul, as a thing by itself, by means of speculative reason (still less through empirical observation), and consequently may not know freedom either, as the quality of a being to which I attribute effects in the world of sense, because, in order to do this, I should have to know such a being as determined in its existence, and yet as not determined in time (which, as I cannot provide my concept with any intuition, is impossible). This, however, does not prevent me from thinking freedom; that is, my representation of it contains at least no contradiction within itself, if only our critical distinction of the two modes of representation (the sensible and the intelligible), and the consequent limitation of the concepts of the pure understanding, and of the principles based on them, has been properly carried out. If, then, morality necessarily presupposed freedom (in the strictest sense) as a property of our will, producing, as a priori data of it, practical principles, belonging originally to our reason, which, without freedom, would be absolutely impossible, while speculative reason had proved that such a freedom cannot even [p. xxix] be thought, the former supposition, namely, the moral one, would necessarily have to yield to another, the opposite of which involves a palpable contradiction, so that freedom, and with it morality (for its opposite contains no contradiction, unless freedom is presupposed), would have to make room for the mechanism of nature. Now, however, as morality requires nothing but that freedom should only not contradict itself, and that, though unable to understand, we should at least be able to think it, there being no reason why freedom should interfere with the natural mechanism of the same act (if only taken in a different sense), the doctrine of morality may well hold its place, and the doctrine of nature may hold its place too, which would have been impossible, if our critique had not previously taught us our inevitable ignorance with regard to things by themselves, and limited everything, which we are able to know theoretically, to mere phenomena. The same discussion as to the positive advantage to be derived from the critical principles of pure reason might be repeated with regard to the concept of God, and of the simple nature of our soul; but, for the sake of brevity, I shall pass this by. I am not allowed therefore even to assume, for the sake [p. xxx] of the necessary practical employment of my reason, God, freedom, and immortality, if I cannot deprive speculative reason of its pretensions to transcendent insights, because reason, in order to arrive at these, must use principles which are intended originally for objects of possible experience only, and which, if in spite of this, they are applied to what cannot be an object of experience, really changes this into a phenomenon, thus rendering all practical extension of pure reason impossible. I had therefore to remove knowledge, in order to make room for belief. For the dogmatism of metaphysic, that is, the presumption that it is possible to achieve anything in metaphysic without a previous criticism of pure reason, is the source of all that unbelief, which is always very dogmatical, and wars against all morality.

If, then, it may not be too difficult to leave a bequest to posterity, in the shape of a systematical metaphysic, carried out according to the critique of pure reason, such a bequest is not to be considered therefore as of little value, whether we regard the improvement which reason receives through the secure method of a science, in place of its groundless groping and uncritical vagaries, or whether we look to the better employment [p. xxxi] of the time of our enquiring youth, who, if brought up in the ordinary dogmatism, are early encouraged to indulge in easy speculations on things of which they know nothing, and of which they, as little as anybody else, will ever understand anything; neglecting the acquirement of sound knowledge, while bent on the discovery of new metaphysical thoughts and opinions. The greatest benefit however will be, that such a work will enable us to put an end for ever to all objections to morality and religion, according to the Socratic method, namely, by the clearest proof of the ignorance of our opponents. Some kind of metaphysic has always existed, and will always exist, and with it a dialectic of pure reason, as being natural to it. It is therefore the first and most important task of philosophy to deprive metaphysic, once for all, of its pernicious influence, by closing up the sources of its errors.

In spite of these important changes in the whole field of science, and of the losses which speculative reason must suffer in its fancied possessions, all general human interests, and all the [p. xxxii] advantages which the world hitherto derived from the teachings of pure reason, remain just the same as before. The loss, if any, affects only the monopoly of the schools, and by no means the interests of humanity. I appeal to the staunchest dogmatist, whether the proof of the continued existence of our soul after death, derived from the simplicity of the substance, or that of the freedom of the will, as opposed to the general mechanism of nature, derived from the subtle, but inefficient, distinction between subjective and objective practical necessity, or that of the existence of God, derived from the concept of an Ens realissimum (the contingency of the changeable, and the necessity of a prime mover), have ever, after they had been started by the schools, penetrated the public mind, or exercised the slightest influence on its convictions? If this has not been, and in fact could not be so, on account of the unfitness of the ordinary understanding for such subtle speculations; and if, on the contrary, with regard to the first point, the hope of a future life has chiefly rested on that peculiar character of human nature, never to be satisfied by what is merely temporal (and insufficient, therefore, for the character of its whole destination); if with regard to the second, the clear consciousness of freedom was produced only by the [p. xxxiii] clear exhibition of duties in opposition to all the claims of sensuous desires; and if, lastly, with regard to the third, the belief in a great and wise Author of the world has been supported entirely by the wonderful beauty, order, and providence, everywhere displayed in nature, then this possession remains not only undisturbed, but acquires even greater authority, because the schools have now been taught, not to claim for themselves any higher or fuller insight on a point which concerns general human interests, than what is equally within the reach of the great mass of men, and to confine themselves to the elaboration of these universally comprehensible, and, for moral purposes, quite sufficient proofs. The change therefore affects the arrogant pretensions of the schools only, which would fain be considered as the only judges and depositaries of such truth (as they are, no doubt, with regard to many other subjects), allowing to the public its use only, and trying to keep the key to themselves, quod mecum nescit, solus vult scire videri. At the same time full satisfaction is given to the more moderate claims of speculative philosophers. [p. xxxiv] They still remain the exclusive depositors of a science which benefits the masses without their knowing it, namely, the critique of reason. That critique can never become popular, nor does it need to be so, because, if on the one side the public has no understanding for the fine-drawn arguments in support of useful truths, it is not troubled on the other by the equally subtle objections. It is different with the schools which, in the same way as every man who has once risen to the height of speculation, must know both the pro’s and the con’s and are bound, by means of a careful investigation of the rights of speculative reason, to prevent, once for all, the scandal which, sooner or later, is sure to be caused even to the masses, by the quarrels in which metaphysicians (and as such, theologians also) become involved, if ignorant of our critique, and by which their doctrine becomes in the end entirely perverted. Thus, and thus alone, can the very root be cut off of materialism, fatalism, atheism, free-thinking, unbelief, fanaticism, and superstition, which may become universally injurious, and finally of idealism and scepticism, also, which are dangerous rather to the schools, and can scarcely ever penetrate into the public. If [p. xxxv] governments think proper ever to interfere with the affairs of the learned, it would be far more consistent with their wise regard for science as well as for society, to favour the freedom of such a criticism by which alone the labours of reason can be established on a firm footing, than to support the ridiculous despotism of the schools, which raise a loud clamour of public danger, whenever the cobwebs are swept away of which the public has never taken the slightest notice, and the loss of which it can therefore never perceive.

Our critique is not opposed to the dogmatical procedure of reason, as a science of pure knowledge (for this must always be dogmatical, that is, derive its proof from sure principles a priori), but to dogmatism only, that is, to the presumption that it is possible to make any progress with pure (philosophical) knowledge, consisting of concepts, and guided by principles, such as reason has long been in the habit of employing, without first enquiring in what way, and by what right, it has come possessed of them. Dogmatism is therefore the dogmatical procedure of pure reason, without a previous criticism of its own powers; and our opposition to this is not intended to defend either that loquacious [p. xxxvi] shallowness which arrogates to itself the good name of popularity, much less that scepticism which makes short work with the whole of metaphysic. On the contrary, our critique is meant to form a necessary preparation in support of a thoroughly scientific system of metaphysic, which must necessarily be carried out dogmatically and strictly systematically, so as to satisfy all the demands, not so much of the public at large, as of the schools, this being an indispensable condition, as it has undertaken to carry out its work entirely a priori, and thus to the complete satisfaction of speculative reason. In the execution of this plan, as traced out by the critique, that is, in a future system of metaphysic, we shall have to follow in the strict method of the celebrated Wolf, the greatest of all dogmatic philosophers, who first showed (and by his example called forth, in Germany, that spirit of thoroughness, which is not yet extinct) how the secure method of a science could be attained only by a legitimate establishment of principles, a clear definition of concepts, an attempt at strictness of proof, and an avoidance of all bold combinations in concluding. He was therefore most eminently qualified to raise metaphysics to the dignity of a science, if it had only occurred to him, by criticism of the organum, namely, of pure reason itself, first to prepare his field, — an omission to be ascribed, not so much to himself as to the dogmatical [p. xxxvii] spirit of his age, and with regard to which the philosophers of his own, as well as of all previous times, have no right to reproach each other. Those who reject, at the same time, the method of Wolf, and the procedure of the critique of pure reason, can have no other aim but to shake off the fetters of science altogether, and thus to change work into play, conviction into opinion, and philosophy into philodoxy.

With regard to this second edition, I have tried, as was but fair, to do all I could in order to remove, as far as possible, the difficulties and obscurities which, not perhaps without my fault, have misled even acute thinkers in judging of my book. In the propositions themselves, and their proofs, likewise in the form and completeness of the whole plan, I have found nothing to alter, which is due partly to the long-continued examination to which I had subjected them, before submitting them to the public, and partly to the nature of the subject itself. For pure speculative reason is so constituted that it forms a true organism, in which everything is organic, the whole being there for the [p. xxxviii] sake of every part, and every part for the sake of the whole, so that the smallest imperfection, whether a fault or a deficiency, must inevitably betray itself in use. I venture to hope that this system will maintain itself unchanged for the future also. It is not self-conceit which justifies me in this confidence, but the experimental evidence produced by the identity of the result, whether we proceed progressively from the smallest elements to the whole of pure reason, or retrogressively from the whole (for this also is given by the practical objects of reason) to every single part; the fact being, that an attempt at altering even the smallest item produces at once contradictions, not only in the system, but in human reason in general. With regard to the style, however, much remains to be done; and for that purpose, I have endeavoured to introduce several improvements into this second edition, which are intended to remove, first, misapprehensions in the Æsthetic, especially with regard to the concept of time: secondly, obscurities in the deduction of the concepts of the understanding: thirdly, a supposed want of sufficient evidence, in proving the propositions of the pure understanding: fourthly, the false interpretation put on the paralogisms with which we charged rational psychology. To this point (only to the end of the first chapter of transcendental Dialectic) do the changes [p. xxxix] of style and representation1 extend, and no further. Time was too short for doing more, nor did I, with regard to the [p. xl] rest, meet with any misapprehensions on the part of [p. xli] competent and impartial judges. These, even though I must not name them with that praise which is due to them, will easily perceive in the proper place, that I have paid careful attention to their remarks. [p. xlii]

These improvements, however, entail a small loss to the reader. It was inevitable, without making the book too voluminous, to leave out or abridge several passages which, though not essential to the completeness of the whole, may yet, as useful for other purposes, be missed by some readers. Thus only could I gain room for my new and more intelligible representation of the subject which, though it changes absolutely nothing with regard to propositions, and even to proofs, yet deviates so considerably from the former, in the method of the treatment here and there, that mere additions and interpolations would not have been sufficient. This small loss, which every reader may easily supply by reference to the first edition, will I hope be more than compensated for by the greater clearness of the present.

I have observed with pleasure and thankfulness in various publications (containing either reviews or separate essays) that the spirit of thoroughness is not yet dead in Germany, but has only been silenced for a short time by the clamour of a fashionable and pretentious licence of thought, and that the difficulties [p. xliii] which beset the thorny path of my critique, which is to lead to a truly scientific and, as such, permanent, and therefore most necessary, science of pure reason, have not discouraged bold and clear heads from mastering my book. To these excellent men, who so happily blend thorough knowledge with a talent for lucid exposition (to which I can lay no claim), I leave the task of bringing my, in that respect far from perfect, work to greater perfection. There is no danger of its being refuted, though there is of its being misunderstood. For my own part, I cannot henceforth enter on controversies, though I shall carefully attend to all hints, whether from friends or opponents, in order to utilise them in a future elaboration of the whole system, according to the plan traced out in this propaedeutic. As during these labours I have advanced pretty far in years (this very month, into my sixty-fourth year), I must be careful in spending my time, if I am to carry out my plan, of furnishing a metaphysic of nature, and a metaphysic of morals, in confirmation of the truth of my critique both of speculative and of practical reason, and must leave the elucidation of such obscurities as could at first be hardly avoided [p. xliv] in such a work, and likewise the defence of the whole, to those excellent men who have made it their own. At single points every philosophical treatise may be pricked (for it cannot be armed at all points, like a mathematical one), while yet the organic structure of the system, considered as a whole, has not therefore to apprehend the slightest danger. Few only have that pliability of intellect to take in the whole of a system, if it is new; still fewer have an inclination for it, because they dislike every innovation. If we take single passages out of their connection, and contrast them with each other, it is easy to pick out apparent contradictions, particularly in a work written with all the freedom of a running speech. In the eyes of those who rely on the judgment of others, such contradictions may throw an unfavourable light on any work; but they are easily removed, if we ourselves have once grasped the idea of the whole. And, if a theory possesses stability in itself, then this action and reaction of praise and blame, which at first seemed so dangerous, serve only in time to rub off its superficial inequalities: nay, secure to it, in a short time, the requisite elegance also, if only men of insight, impartiality, and true popularity will devote themselves to its study.

Königsberg, April, 1787.

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

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

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

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

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

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

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