Appendix

Appendix

On what can be done to make metaphysics actual as a science.

Since none of the paths taken so far has reached this goal, and it will probably never be reached without a prior critique of pure reason, it seems no unreasonable demand that the attempt now laid before us be subjected to an exact and careful examination—unless one considers it more advisable to abandon all claims to metaphysics altogether. In that case there is no objection, provided one remains faithful to the resolution. If we take the course of things as it actually runs, not as it ought to run, there are two kinds of judgment: a judgment that precedes investigation, such as, in our case, the reader’s judgment of the Critique of Pure Reason from the standpoint of his own metaphysics, although the Critique is first to investigate the very possibility of metaphysics; and another judgment that follows investigation, in which the reader can for a time set aside the consequences of the critical inquiries, which may clash sharply with the metaphysics he has hitherto accepted, and first examine the grounds from which those consequences may have been derived. If what ordinary metaphysics teaches were established as certain, as geometry is, for example, the first manner of judging would hold good. For if the consequences of certain principles contradict established truths, those principles are false and must be rejected without any further investigation. But if metaphysics has no stock of indisputably certain synthetic propositions; if, perhaps, many of its propositions, as plausible as the best of them, nevertheless conflict with one another in their consequences; and if no secure criterion at all for the truth of properly metaphysical, synthetic propositions is to be found in it, then the preceding manner of judging is inadmissible. An investigation of the principles of critique must precede every judgment of its worth or worthlessness.

An example of a judgment of the Critique that precedes investigation.

A judgment of this kind is to be found in the Göttingische gelehrte Anzeigen, supplement, third issue, January 19, 1782, page 40 and following.

When an author thoroughly acquainted with the subject of his work, who has endeavored throughout to bring his own reflection to its treatment, falls into the hands of a reviewer perceptive enough to discern the points on which the work’s worth or worthlessness really depends, who does not cling to words but pursues the matters themselves, and does not merely sift and test the principles from which the author began, the author may indeed dislike the severity of the judgment. The public is indifferent to this, for it gains by it. And the author himself can be satisfied that he has an opportunity to correct or clarify his arguments, examined early on by someone who understands the subject, and thus, if he believes himself fundamentally right, to remove in good time a stumbling block that might later harm his work.

With my reviewer I find myself in an entirely different position. He seems not to understand at all what really mattered in the inquiry on which I was engaged, successfully or not. Whether the fault lies in impatience at thinking through an extensive work, in a peevish mood at the threatened reform of a science in which he believed he had long since settled everything, or—what I am reluctant to suspect—in a genuinely narrow conception that prevents him from ever thinking beyond his school metaphysics: in short, he rushes headlong through a long series of propositions from which, without knowing their premises, one can make no sense at all. Here and there he scatters his censure, whose grounds the reader can no more discern than he can understand the propositions against which it is supposed to be directed. He can therefore neither help inform the public nor do me the slightest harm in the judgment of those who understand the subject. I would accordingly have passed over this review altogether, had it not given me occasion for a few clarifications that may in some cases protect the reader of these Prolegomena from misinterpretation.

Yet in order to seize on a standpoint from which he can most easily present the entire work in a light unfavorable to its author, without troubling himself with any particular investigation, the reviewer begins and ends by saying: “This work is a system of transcendental—or, as he translates it, higher^373.1—idealism.”

At the sight of this line I soon knew what sort of review would emerge. It was much as if someone who had never heard of or seen anything of geometry found a copy of Euclid and was asked to judge it. Having come across many figures as he leafed through it, he might say: “The book is a systematic guide to drawing. The author uses a peculiar language to give obscure, unintelligible instructions, which in the end can accomplish no more than anyone can achieve with a good natural eye, etc.”

Let us nevertheless see what sort of idealism it is that runs throughout my work, although it is far from constituting the soul of the system.

The proposition of all genuine idealists, from the Eleatic school to Bishop Berkeley, is contained in this formula: “All cognition through the senses and experience is nothing but sheer illusion, and only in the ideas of pure understanding and reason is there truth.”

The principle that governs and determines my idealism throughout, by contrast, is this: “All cognition of things from mere pure understanding or pure reason is nothing but sheer illusion, and only in experience is there truth.”

But this is precisely the opposite of that idealism proper. How, then, did I come to use this expression for an entirely opposite purpose, and how did the reviewer come to see it everywhere?

The solution to this difficulty rests on something that could very easily have been discerned from the context of the work, had one wished to do so. Space and time, together with everything they contain, are not things or their properties in themselves, but belong only to their appearances. Up to this point I profess the same belief as those idealists. But they, and Berkeley above all, regarded space as a merely empirical representation, which, like the appearances within it, becomes known to us with all its determinations only through experience or perception. I, by contrast, first show that space, and likewise time, to which Berkeley paid no attention, can be cognized by us a priori together with all its determinations. For space, as well as time, belongs to us before all perception or experience as the pure form of our sensibility, making possible all its intuition and therefore all appearances as well. It follows that, since truth rests on universal and necessary laws as its criteria, experience for Berkeley can have no criteria of truth: he laid nothing a priori at the foundation of its appearances, from which it followed that experience was nothing but sheer illusion. For us, by contrast, space and time, in conjunction with the pure concepts of the understanding, prescribe a priori the law for all possible experience, which at the same time provides the secure criterion for distinguishing truth from illusion within it.^375.1

My so-called idealism, properly speaking critical idealism, is therefore of an entirely distinctive kind: it overturns ordinary idealism, and through it all a priori cognition, even that of geometry, first acquires objective reality. Without the ideality of space and time that I have proved, not even the most zealous realists could assert that reality. Under these circumstances, I wish I could give this conception of mine another name, to prevent every misunderstanding; but changing the term altogether is scarcely feasible. Let me therefore be permitted in the future, as already mentioned above, to call it formal, or better still critical, idealism, to distinguish it from the dogmatic idealism of Berkeley and the skeptical idealism of Descartes.

I find nothing else remarkable in the review of this book. Its author judges throughout en gros, a manner shrewdly chosen, since it betrays neither one’s own knowledge nor one’s ignorance. A single detailed judgment en détail, had it properly addressed the principal question, might have exposed my error, or perhaps the measure of the reviewer’s insight into inquiries of this kind. Nor was it an ill-conceived stratagem for depriving readers who habitually form their idea of books solely from journal notices of any desire to read the book itself: to rush through a mass of propositions in a single breath, propositions that, torn from their connection with their proofs and explanations, must necessarily sound absurd, especially when they are so diametrically opposed to all school metaphysics as these are; to batter the reader’s patience to the point of disgust; and then, after acquainting me with the ingenious proposition that enduring illusion is truth, to close with the blunt but paternal lesson: “Why this quarrel with commonly accepted language? Why, and from what source, this idealistic distinction?” A judgment that in the end reduces everything distinctive in my book to a mere innovation in language, after declaring it metaphysical heresy, and clearly proves that my self-appointed judge has understood not the slightest thing about it, and has not properly understood even himself.^376.1

The reviewer nevertheless speaks like a man who must be conscious of important and exceptional insights, which he still keeps hidden; for nothing in metaphysics has recently come to my attention that could justify such a tone. But he does the world a great wrong by withholding his discoveries. For no doubt others are in the same position as I am: despite all the fine things written in this field for a long time, they have been unable to find that the science has advanced a finger’s breadth. One certainly still finds definitions sharpened, lame proofs fitted with new crutches, fresh patches or an altered cut given to the patchwork of metaphysics—but that is not what the world asks for. The world is sated with metaphysical assertions. What people want is the possibility of this science, the sources from which certainty in it can be derived, and secure criteria for distinguishing the dialectical illusion of pure reason from truth. The reviewer must possess the key to this, or he would never have spoken in so lofty a tone.

But I begin to suspect that such a need of the science may never have entered his thoughts. Otherwise he would have directed his review to this point, and even a failed attempt in so important a matter would have earned his respect. If that is so, we are good friends again. Let him think his way as deeply into his metaphysics as he likes; no one shall hinder him. Only he cannot judge what lies outside metaphysics: its source within reason. That my suspicion is not groundless I prove by this: he did not mention a word about the possibility of synthetic a priori cognition, which was the real problem, on whose solution the fate of metaphysics entirely depends, and to which my Critique, just like my Prolegomena here, was wholly directed. The idealism he stumbled on and remained stuck at was incorporated into the doctrine only as the sole means of solving that problem, although it also received confirmation on other grounds. Here he ought to have shown either that the problem lacks the importance I assign it, as I do again now in the Prolegomena, or that my concept of appearances cannot solve it at all, or that it can be better solved in some other way. But I find not a word of this in the review. The reviewer therefore understood nothing of my work, and perhaps nothing of the spirit and essence of metaphysics itself—unless, as I prefer to assume, it was rather a reviewer’s haste, indignant at the difficulty of working through so many obstacles, that cast an unfavorable shadow over the work before him and made its fundamental features unrecognizable to him.

A learned journal is still very far from being able to maintain in the field of metaphysics the standing it otherwise deserves, as it does in other fields, however well and carefully its contributors may be chosen. Other sciences and branches of knowledge do, after all, have their standards. Mathematics has its standard within itself; history and theology have theirs in secular or sacred books; natural science and medicine in mathematics and experience; jurisprudence in law books; and even matters of taste in the models of the ancients. But for judging the thing called metaphysics, the standard has yet to be found. I have attempted to determine both the standard and its use. What, then, is to be done until it has been discovered, if writings of this kind must nonetheless be judged? If they are dogmatic, one may proceed as one likes: no one will long play the master over another in this field without someone appearing to repay him in kind. But if they are critical, not with regard to other writings but to reason itself, so that the standard of judgment cannot already be assumed but is only now being sought, objections and censure need not be unwelcome. Yet a spirit of tolerance must underlie them, for the need is shared, and the lack of the requisite insight makes the authority of a judge delivering a verdict inadmissible.

To connect this defense of mine with the interests of the philosophizing community as well, I propose a trial that will decide how all metaphysical inquiries must be directed toward their common goal. It is nothing other than what mathematicians have sometimes done to decide, in a contest, the superiority of their methods: a challenge to my reviewer to prove in his own way any single genuinely metaphysical proposition he asserts—that is, a synthetic proposition cognized a priori from concepts. It may even be one of the most indispensable: for example, the principle of the persistence of substance, or of the necessary determination of events in the world by their cause. But he must prove it, as is proper, on a priori grounds. If he cannot—and silence is an admission—he must concede that, since metaphysics is absolutely nothing without apodictic certainty in propositions of this kind, its possibility or impossibility must before all else first be settled in a critique of pure reason. He is therefore bound either to confess that my principles of critique are correct or to prove their invalidity. Yet I can already foresee that, however confidently he has so far relied on the certainty of his principles, when it comes to a rigorous test he will not find a single one in the whole compass of metaphysics that he can boldly put forward. I will therefore grant him the most favorable condition one could expect in a contest: I will relieve him of the onus probandi and take it upon myself.

For in these Prolegomena and in my Critique, pp. 426–461, he will find eight propositions, arranged in mutually contradictory pairs, while every one necessarily belongs to metaphysics, which must either accept or refute it—although there is not one that has not at some time been accepted by some philosopher. He is now free to choose whichever of these eight propositions he likes and accept it without proof, which I waive for him—but only one, since wasting time will serve him as little as it serves me—and then to attack my proof of its opposite. If I can nevertheless uphold this proof, and thus show that, according to principles every dogmatic metaphysics must necessarily acknowledge, the opposite of his adopted proposition can be proved just as clearly, it is thereby established that metaphysics has an inherited defect. This defect cannot be explained, much less remedied, unless we ascend to its birthplace, pure reason itself. My Critique must then either be accepted or replaced by a better one, and thus must at least be studied, which is all I ask for now. If, on the contrary, I cannot uphold my proof, then a synthetic a priori proposition established from dogmatic principles stands firm on my opponent’s side; my charge against ordinary metaphysics was therefore unjust; and I offer to acknowledge his censure of my Critique as legitimate, although that would still be far from following. For this, however, I think he would need to emerge from his anonymity. Otherwise I do not see how to prevent unnamed and yet uninvited opponents from honoring or assailing me with several challenges instead of one.

Proposal for an investigation of the Critique after which judgment may follow.

I am also indebted to the learned public for the silence with which it has honored my Critique for a considerable time. For this at least shows a suspension of judgment, and thus some inkling that a work which leaves all the familiar paths and strikes out on a new one, on which one cannot immediately find one’s way, may nevertheless contain something capable of giving new life and fruitfulness to an important but now dead branch of human cognition. It therefore shows a caution against breaking off and destroying the still tender graft by a hasty judgment. An example of a judgment delayed on such grounds has just now come before my eyes in the Gothaische gelehrte Zeitung. Every reader will perceive its thoroughness for himself, without taking into account my praise, which is suspect in this matter, from its comprehensible and undistorted presentation of a part belonging to the first principles of my work.

And now, since an extensive building cannot possibly be judged immediately as a whole by a cursory survey, I propose that it be examined piece by piece, beginning with its foundation, using the present Prolegomena as a general outline with which the work itself could then be compared as occasion arises. If this request rested on nothing more than my own fancy of its importance, which vanity ordinarily lends to all one’s own productions, it would be immodest and deserve to be rejected with indignation. But the affairs of all speculative philosophy now stand on the verge of complete extinction, although human reason clings to them with an inclination that never dies. Only because it is incessantly deceived does this inclination now try, though in vain, to turn itself into indifference.

In our thinking age, we cannot suppose that many deserving men would fail to take every good opportunity to work together in the common interest of reason, which is becoming ever more enlightened, if only there is some hope of thereby reaching the goal. Mathematics, natural science, laws, arts, even morality, etc., still do not fill the soul entirely. There always remains a space in it marked out for mere pure and speculative reason. Its emptiness compels us to seek in grotesque fancies, trifles, or even visionary enthusiasm what appears to be occupation and entertainment, but is at bottom only distraction, to drown out the importunate call of reason. In accordance with its vocation, reason demands something that will satisfy it in itself, not merely keep it busy serving other purposes or the interests of inclinations. A consideration devoted solely to this sphere of reason subsisting for itself therefore has, as I have grounds to suppose, a great attraction for anyone who has even tried to extend his concepts this far, precisely because within this sphere all other branches of knowledge, and even ends, must converge and unite into a whole. I may well say that its attraction is greater than that of any other theoretical knowledge, which one would not readily take in exchange for it.

But I propose these Prolegomena as the plan and guiding thread of the inquiry, rather than the work itself, for this reason. I am still entirely satisfied with that work as regards its content, arrangement, method of instruction, and the care spent on weighing and testing each proposition precisely before setting it down. For it took years to satisfy myself fully about the sources not only of the whole, but sometimes of even a single proposition. Yet I am not entirely satisfied with my exposition in some sections of the Doctrine of Elements, such as the deduction of the concepts of the understanding or the section on the paralogisms of pure reason. A certain prolixity in them impedes clarity. In their place, what the Prolegomena say here concerning those sections may serve as the basis of examination.

The Germans are praised for their ability to advance further than other nations in whatever requires perseverance and sustained diligence. If this opinion is well founded, here is an opportunity to bring to completion an undertaking whose happy outcome can scarcely be doubted, in which all thinking people have an equal interest, but which has hitherto been unsuccessful, and thus to confirm that favorable opinion. This is especially so since the science concerned is of such a peculiar kind that it can be brought all at once to its entire completeness and to that stable condition in which it can be advanced no further in the least, nor enlarged or even altered by later discoveries. I do not count here embellishments through greater clarity here and there, or through added usefulness in various respects. This is an advantage that no other science has or can have, since none concerns a cognitive capacity so completely isolated, independent of others, and unmixed with them. Nor does the present moment seem unfavorable to my request. For in Germany now one scarcely knows what else to occupy oneself with, beyond the so-called useful sciences, that would not be mere play but also an undertaking through which a lasting end is achieved.

I must leave to others the devising of means by which the efforts of scholars could be united for such a purpose. Meanwhile, I do not intend to demand that anyone merely follow my propositions, or even to flatter myself with the hope of it. Rather, attacks, repetitions, restrictions, or else confirmations, additions, and extensions may arise as circumstances warrant. If only the matter is investigated from the ground up, it can now no longer fail to produce a system of doctrine, even if not my own, that can become a legacy to posterity for which it will have reason to be grateful.

What sort of metaphysics may be expected to follow from critique, once its principles have first been put on a sound footing, and how metaphysics, once stripped of its borrowed plumage, need by no means appear impoverished and reduced to an insignificant figure, but can in another respect appear richly and fittingly furnished, would take too long to show here. But other great benefits that such a reform would bring are immediately evident. Ordinary metaphysics was already useful in seeking out the elementary concepts of the pure understanding, in order to make them clear through analysis and determinate through definitions. It thereby became a means of cultivating reason, wherever reason might later see fit to turn. But that was all the good it did. For it nullified this merit in turn by encouraging conceit through rash assertions, sophistry through subtle evasions and glosses, and shallowness through the ease of disposing of the most difficult problems with a little school wisdom. This shallowness is all the more seductive the more it can choose to assume something of the language of science on the one hand and of popular accessibility on the other, and thus be all things to everyone, while in fact being nothing at all. Through critique, by contrast, our judgment is given a standard by which knowledge can be securely distinguished from sham knowledge. By being put fully into practice in metaphysics, critique establishes a way of thinking whose beneficial influence then extends to every other use of reason, and for the first time instills the true philosophical spirit. Nor should we underestimate the service it renders theology by making it independent of the judgment of dogmatic speculation, and thereby placing it in complete security against every attack from such opponents. For ordinary metaphysics, though it promised theology much support, could not afterward fulfill that promise. Moreover, by calling speculative dogmatism to its aid, it had done nothing but arm enemies against itself. Visionary enthusiasm, which in an enlightened age can gain ground only by hiding behind a school metaphysics, under whose protection it may dare to rave with reason, as it were, is driven by critical philosophy from this last hiding place. And beyond all this, it can hardly fail to matter to a teacher of metaphysics that he should at last be able to say, with general assent, that what he teaches is now finally science as well, and that a real benefit is thereby rendered to the community.

373.1. By no means higher. High towers and the metaphysically great men who resemble them, both usually surrounded by much wind, are not for me. My place is the fertile bathos of experience. The word transcendental, whose meaning I have indicated so often and which the reviewer has not even grasped—so cursorily has he looked at everything—does not mean something that goes beyond all experience, but something that does precede experience a priori, yet is destined for nothing more than making cognition of experience possible. When these concepts overstep experience, their use is called transcendent, as distinguished from their immanent use, that is, their use restricted to experience. The work has sufficiently guarded against all misinterpretations of this kind; but the reviewer found misinterpretations to his advantage.

375.1. Idealism proper has always had a visionary purpose and can have no other. Mine, however, serves solely to comprehend the possibility of our a priori cognition of objects of experience, a problem that has never yet been solved, or even raised. This brings down the whole of visionary idealism, which always inferred from our a priori cognitions, even those of geometry, an intuition other than that of the senses, namely an intellectual one, as can already be seen in Plato. For it never occurred to anyone that the senses too might intuit a priori.

376.1. The reviewer is mostly fighting his own shadow. When I contrast the truth of experience with a dream, it never occurs to him that the question here concerns only the familiar somnio objective sumto of Wolffian philosophy, which is merely formal. It has nothing to do with the distinction between sleeping and waking, nor can it have in a transcendental philosophy. Moreover, he calls my deduction of the categories and the table of principles of the understanding “commonly known principles of logic and ontology, expressed in an idealistic manner.” The reader need only consult these Prolegomena on this point to be convinced that a more wretched judgment, or even a more historically incorrect one, could not possibly be delivered.

Appendix

On what can be done to make metaphysics an actual science.

All the paths followed so far have failed to reach this goal. Nor is it ever likely to be reached without a prior critique of pure reason. So it seems reasonable to ask that the attempt now presented be examined closely and carefully. The alternative is to consider it wiser to give up all claims to metaphysics altogether. There is no objection to that course, provided people stay true to their decision. If we take events as they actually unfold, rather than as they should, there are two kinds of judgment. One is a judgment made before the investigation. In our case, this occurs when a reader uses his own metaphysics to judge the critique of pure reason, whose task is first to investigate whether metaphysics is possible. The other is a judgment made after the investigation. Here the reader can put aside for a while the consequences of the critical investigations, which may conflict sharply with the metaphysics he has accepted until now. He first examines the grounds from which those consequences may have been derived. If the claims of ordinary metaphysics were settled certainties, like those of geometry, the first kind of judgment would be valid. For if the consequences of certain principles conflict with established truths, those principles are false and must be rejected without further investigation. But suppose metaphysics does not possess a stock of indisputably certain synthetic propositions. Perhaps many of its propositions, as plausible as the best of them, even conflict with one another in their consequences. And suppose it has no reliable criterion at all for the truth of genuinely metaphysical, synthetic propositions. In that case, the first way of judging cannot apply. The principles of critique must be investigated before any judgment is made about their value or worthlessness.

Example of a judgment on the Critique made before investigation.

A judgment of this kind appears in the Göttingische gelehrte Anzeigen, the supplement's third issue, January 19, 1782, page 40 and following.

Suppose an author knows the subject of his work well and has worked hard to bring his own thinking to every part of it. His work falls into the hands of a reviewer sharp enough to spot the points on which its value or worthlessness really depends. The reviewer does not get stuck on words but follows the substance of the argument, and does more than merely inspect and test the principles from which the author started. The author may dislike the severity of the judgment, but the public need not mind, because it benefits. The author himself can be glad to have an opportunity to correct or clarify his arguments after an expert has tested them early on. If he believes he is basically right, he can thus remove in good time an obstacle that might later damage his work.

My situation with my reviewer is entirely different. He seems not to see at all what really mattered in the investigation I undertook, successfully or unsuccessfully. Perhaps he was impatient with thinking through a long work. Perhaps he was irritated by the threat of reforming a science in which he thought he had long since settled everything. Or perhaps, as I am reluctant to suspect, the cause was a genuinely limited outlook that keeps him from ever thinking beyond his school metaphysics. In short, he rushes aggressively through a long series of propositions that mean nothing to anyone who does not know their premises. He scatters criticisms here and there. The reader can no more see the grounds for these criticisms than understand the propositions they are directed against. So the review can neither usefully inform the public nor do me the slightest damage in the judgment of experts. I would therefore have ignored it altogether if it had not given me an opportunity for a few clarifications. These may protect the reader of these Prolegomena from misunderstandings in certain cases.

The reviewer wants a viewpoint from which he can most easily present the whole work unfavorably to its author, without having to undertake any particular investigation. So he begins, and also ends, by saying: “This work is a system of transcendental—or, as he translates it, higher—^373.1 idealism.”

As soon as I saw this line, I knew what sort of review would follow. It was much as if someone who had never heard or seen anything of geometry found a copy of Euclid and was asked to judge it. After leafing through it and coming across many figures, he might say: “This book is a systematic guide to drawing. The author uses a special language to give obscure, unintelligible instructions. In the end they can achieve no more than anyone can manage with a naturally good eye, etc.”

Still, let us see what kind of idealism this is. It runs through my whole work, although it is far from constituting the heart of the system.

The position of all genuine idealists, from the Eleatic school to Bishop Berkeley, is contained in this formula: “All cognition through the senses and experience is nothing but illusion. Truth is found only in the ideas of pure understanding and reason.”

By contrast, the principle that governs and defines my idealism throughout is this: “All cognition of things through mere pure understanding or pure reason is nothing but illusion. Truth is found only in experience.”

But that is the exact opposite of idealism in the strict sense. How, then, did I come to use this expression for a completely opposite purpose? And how did the reviewer come to see it everywhere?

The solution to this difficulty depends on something that could very easily have been understood from the work's context, if anyone had wanted to understand it. Space and time, together with everything they contain, are not things or their properties in themselves. They belong only to the appearances of things. So far I agree with those idealists. But they, especially Berkeley, considered space a merely empirical representation. On their view, space and all its determinations become known to us only through experience or perception, just like the appearances within it. I, by contrast, first show that we can know space and all its determinations a priori. The same holds for time, which Berkeley did not consider. Space, like time, is present in us before all perception or experience as the pure form of our sensibility. It makes every intuition of sensibility possible, and therefore every appearance as well. Truth depends on universal and necessary laws as its criteria. It follows that for Berkeley experience can have no criteria of truth, because he gave its appearances no a priori foundation. The result was that experience was nothing but illusion. On our account, by contrast, space and time, combined with the pure concepts of the understanding, prescribe their law a priori to all possible experience. This law also provides a reliable criterion for distinguishing truth from illusion within experience.^375.1

My so-called idealism, which is properly critical idealism, is therefore of an entirely distinctive kind. It overturns ordinary idealism. Through it, all a priori cognition, even geometry, gains objective reality for the first time. Without the ideality of space and time that I have proved, even the most committed realists could not maintain that objective reality. Under these circumstances, I wish I could give my concept a different name to prevent every misunderstanding. But changing its name altogether would hardly be workable. So let me call it in future, as I already did above, formal idealism, or better still, critical idealism. This distinguishes it from Berkeley's dogmatic idealism and Descartes's skeptical idealism.

I find nothing else worth noting in the review of this book. Its author judges everything in broad terms, a cleverly chosen method, since it does not reveal what he knows or does not know. A single detailed judgment, if it had properly addressed the main question, might have exposed my error. Or it might have exposed the extent of the reviewer's insight into this kind of investigation. His other tactic was also not badly devised. Some readers are used to forming their opinions of books solely from newspaper reports. To discourage them from reading the book itself right from the start, he races in one breath through a mass of propositions torn from their supporting arguments and explanations. In that state they must sound absurd, especially when they are as completely opposed to all school metaphysics as mine are. He assaults the reader's patience to the point of disgust. Then, after introducing me to the ingenious proposition that lasting illusion is truth, he ends with a blunt but fatherly lecture: “Why this dispute with generally accepted language? What is the point of the idealistic distinction, and where does it come from?” This judgment finally reduces everything distinctive about my book to a mere innovation in language, though earlier it was supposed to be metaphysical heresy. It clearly proves that my self-appointed judge has not understood the slightest thing about the book, and has not properly understood himself either.^376.1

Yet the reviewer speaks like a man who must be aware of important and outstanding insights that he is still keeping hidden. I have recently learned of nothing in metaphysics that could justify such a tone. But he is very wrong to withhold his discoveries from the world. No doubt others have had the same experience as I have. Despite all the fine things written in this field for a long time, they have been unable to find that these writings have advanced the science by even a finger's width. We do still find sharpened definitions, new crutches for lame proofs, and new patches or a different cut for metaphysics' patchwork garment. But that is not what the world wants. The world has had enough of metaphysical assertions. People want to know whether this science is possible, what sources can provide certainty in it, and what reliable criteria distinguish pure reason's dialectical illusion from truth. The reviewer must possess the key to this. Otherwise he would never have spoken in such a lofty tone.

But I begin to suspect that this need of the science may never have entered his mind. Otherwise he would have directed his review to this point. Even an unsuccessful attempt in so important a matter would have earned his respect. If that is the situation, we are good friends again. He may think his way as deeply into his metaphysics as he likes. No one should stop him. But he cannot judge what lies outside metaphysics: its source within reason. My suspicion is not groundless. The proof is that he said not a word about the possibility of synthetic a priori cognition. That was the real problem. The entire fate of metaphysics depends on its solution, and my Critique, just like these Prolegomena, was directed wholly toward it. The idealism he stumbled upon and then got stuck on was included in the doctrine only as the sole means of solving that problem, though it was also confirmed on other grounds. He should therefore have shown one of three things: that the problem is not as important as I claim, here in the Prolegomena as well; that my concept of appearances does not solve it at all; or that it can be solved better in some other way. But I find not a word of this in the review. So the reviewer understood nothing of my work, and perhaps nothing of the spirit and nature of metaphysics itself. Or perhaps, as I prefer to assume, his haste as a reviewer was irritated by the difficulty of working through so many obstacles. This cast an unfavorable shadow over the work before him and made even its basic outlines unrecognizable to him.

A learned journal has a very long way to go before it can maintain in metaphysics the reputation it otherwise deserves, however carefully and well its contributors are chosen. Other sciences and branches of knowledge have their standards. Mathematics has its standard within itself. History and theology have theirs in secular or sacred books. Natural science and medicine have theirs in mathematics and experience. Law has its codes, and even matters of taste have the models of antiquity. But the standard for judging what is called metaphysics has yet to be found. I have tried to define both that standard and its use. Until it is established, what should we do when works of this kind still have to be judged? If they are dogmatic, people may do as they please. No one will play the master over someone else here for long without finding someone to pay him back in kind. But suppose the works are critical, and their criticism is directed not at other writings but at reason itself. The standard of judgment cannot then already be assumed; it must first be sought. In that case objections and criticism are welcome, but they must rest on mutual tolerance. The need is shared, and the lack of the necessary insight makes any claim to a judge's decisive authority inappropriate.

To connect this defense of mine with the interests of the philosophical community, I propose a test. It will settle how all metaphysical investigations must be directed toward their shared goal. The proposal is simply what mathematicians have sometimes done to decide the superiority of their methods in a competition. I challenge my reviewer to use his own method to prove any single genuinely metaphysical proposition he asserts. It must, that is, be synthetic and known a priori from concepts. He may even choose one of the most indispensable, such as the principle that substance persists, or that events in the world are necessarily determined by their causes. But he must prove it properly, on a priori grounds. If he cannot do this—and silence counts as an admission—he must concede the following. Without the absolute certainty of propositions of this kind, metaphysics is nothing at all. So before anything else, its possibility or impossibility must be settled in a critique of pure reason. He is therefore bound either to admit that my principles of critique are correct or to prove them invalid. He has so far relied quite confidently on the certainty of his principles. But I can already foresee that, when it comes to a strict test, he will not find a single one in the whole range of metaphysics that he can confidently put forward. So I will grant him the most favorable terms anyone could expect in a contest. I will take the burden of proof off him and place it on myself.

In these Prolegomena and in my Critique, pages 426–461, he will find eight propositions. The propositions contradict one another in pairs. Yet every proposition necessarily belongs to metaphysics, which must either accept it or refute it. In fact, every one of them has at some time been accepted by some philosopher. He is now free to choose whichever of these eight propositions he likes and accept it without proof. I waive that requirement for him. But he must choose only one, since wasting time serves him no better than it serves me. He can then attack my proof of the opposite proposition. Suppose I can still defend my proof and show in this way that the opposite of his chosen proposition can be proved just as clearly from principles that every dogmatic metaphysics must necessarily acknowledge. This will establish that metaphysics has an inborn defect. The defect cannot be explained, much less removed, unless we go back to its birthplace, pure reason itself. My Critique must then either be accepted or replaced by a better one. At the very least, it must be studied. That is all I ask for now. If, on the other hand, I cannot defend my proof, then a synthetic a priori proposition based on dogmatic principles is established on my opponent's side. My accusation against ordinary metaphysics was therefore unjust. I offer in that case to recognize his criticism of my Critique as justified, though this would still be far from following from the result. For this purpose, however, I think he would have to stop remaining anonymous. Otherwise I do not see how I could avoid being honored, or assailed, with several challenges instead of one by unnamed and still uninvited opponents.

Proposal for an investigation of the Critique that can be followed by a judgment.

I am grateful to the learned public even for the silence with which it has honored my Critique for a considerable time. This at least shows a suspension of judgment. It suggests some suspicion that a work which leaves every familiar path and takes a new one, not immediately easy to follow, may still contain something worthwhile. Perhaps it can give new life and fruitfulness to an important but now lifeless branch of human knowledge. The silence therefore shows caution about breaking off and destroying this still tender graft with a hasty judgment. Just now an example of a judgment delayed for such reasons has come to my attention in the Gothaische gelehrte Zeitung. Every reader will recognize its thoroughness from the clear and undistorted presentation of a point belonging to my work's first principles, without needing to consider my praise, which is suspect in this matter.

A large building cannot possibly be judged as a whole straight away by a quick survey. So I now propose that my work be examined piece by piece, starting from its foundations. These Prolegomena can serve as a general outline, with which the work itself can be compared from time to time. If this request rested on nothing but my imagined sense of importance, which vanity usually gives all our own products, it would be immodest and deserve an irritated rejection. But the affairs of speculative philosophy as a whole are now on the point of dying out completely. Human reason still clings to them with an undying inclination. Only because it is constantly disappointed does that inclination now try, though in vain, to turn itself into indifference.

In our reflective age, we cannot suppose that many deserving men would fail to use every good opportunity to work for the shared interests of reason as it becomes increasingly enlightened. They need only some hope that their efforts can reach the goal. Mathematics, natural science, laws, the arts, even morality, and so on, do not yet fill the mind completely. A space always remains in it, set aside for pure speculative reason alone. Its emptiness forces us to seek what looks like occupation and entertainment in absurdities, trivial games, or even wild fantasies. In reality, we seek only distraction to drown out reason's troublesome call. In keeping with its purpose, reason demands something that will satisfy it for its own sake, not merely keep it busy serving other goals or the interests of our inclinations. An investigation concerned solely with this sphere of reason, which stands on its own, therefore has a great appeal, as I have good grounds to suppose, for anyone who has tried to extend his concepts this far. For it is precisely within this sphere that all other knowledge, and even all goals, must meet and unite into a whole. I may even say that it has a greater appeal than any other theoretical knowledge, which one would not readily accept in exchange for it.

I propose these Prolegomena, rather than the work itself, as the plan and guide for the investigation for the following reason. I am still quite satisfied with the work's content, its order and method of teaching, and the care given to each proposition. Before putting any proposition forward, I weighed and tested it carefully. It took years to satisfy myself fully about the whole, and sometimes even about the sources of a single proposition. But I am not fully satisfied with my presentation in some sections of the Doctrine of Elements, such as the deduction of the concepts of the understanding or the section on the paralogisms of pure reason. A certain wordiness in these sections gets in the way of clarity. Instead, the examination can be based on what these Prolegomena say about those sections.

Germans are praised for being able to go further than other peoples in tasks requiring perseverance and sustained hard work. If this opinion is justified, here is an opportunity to confirm it. We can bring to completion a task that has not yet succeeded, although its successful outcome can hardly be doubted and all thinking people share an equal interest in it. This is especially so because the science concerned is of such a distinctive kind. It can be brought all at once to full completion and to that stable condition in which it cannot be advanced in the slightest. Later discoveries can neither enlarge it nor even change it. I am not counting refinements that increase clarity here and there, or added usefulness for various purposes. No other science has this advantage or can have it, because none concerns a cognitive capacity so completely isolated, independent of others, and unmixed with them. The present moment also seems favorable to my request. In Germany today, people scarcely know what they can occupy themselves with apart from the so-called useful sciences, if the occupation is to be not just play but also work that achieves a lasting goal.

I must leave it to others to devise ways of combining the efforts of scholars toward such a goal. But I do not mean to ask anyone simply to follow my propositions, or even to flatter myself with the hope that they will. There may be attacks, repetitions, limitations, or, on the other hand, confirmation, additions, and extensions, as the case may be. If only the matter is investigated from the ground up, a system of doctrine can no longer fail to emerge, even if it is not mine. It can become a legacy to posterity for which later generations will have reason to be grateful.

It would take too long to show here what kind of metaphysics we can expect from the principles of critique once those principles have been properly established. Removing its borrowed feathers need not leave metaphysics looking poor and insignificant. In another respect it can appear richly and suitably equipped. But the other great benefits of such a reform are immediately clear. Ordinary metaphysics already did some good by seeking out the elementary concepts of pure understanding, making them clear through analysis and precise through definitions. In this way it trained reason for whatever use reason might later choose to make of itself. But that was all the good it did. It canceled this merit by encouraging conceit through reckless assertions, sophistry through subtle evasions and excuses, and shallowness through the ease of disposing of the hardest problems with a little school learning. This shallowness is all the more seductive because it can choose to borrow something from the language of science on one side and from popular appeal on the other. It thereby becomes all things to everyone, but in reality is nothing at all. Critique, by contrast, gives our judgment a standard by which knowledge can reliably be distinguished from the mere appearance of knowledge. By being put fully into practice in metaphysics, critique establishes a way of thinking whose beneficial influence then extends to every other use of reason. For the first time, it instills the true philosophical spirit. Nor should we underestimate its service to theology. It makes theology independent of the judgment of dogmatic speculation and thereby secures it completely against all attacks by opponents of that kind. Ordinary metaphysics promised theology much support but could not later fulfill the promise. Worse, by calling speculative dogmatism to its aid, it had done nothing but arm enemies against itself. In an enlightened age, fanatical fantasy can arise only by hiding behind a school metaphysics. Under that protection it dares to rave with reason, so to speak. Critical philosophy drives it out of this last hiding place. Beyond all this, it must surely matter to a teacher of metaphysics that he can at last say, with general agreement, that what he teaches is finally science, and that it therefore provides a real benefit to the community.

373.1. Certainly not higher. High towers and the metaphysically great men who resemble them are not for me. There is usually plenty of wind around both. My place is the fertile depths of experience. The word transcendental does not mean something that goes beyond all experience. It means something that precedes experience a priori, but is intended for nothing more than making knowledge through experience possible. I have explained its meaning in so many ways, yet the reviewer has not even grasped it. That is how superficially he looked at everything. When these concepts go beyond experience, their use is called transcendent. This is distinguished from their immanent use, that is, use restricted to experience. The work has taken sufficient precautions against all misinterpretations of this kind. But the reviewer found misinterpretations to his advantage.

375.1. Idealism in the strict sense always has an aim of indulging in speculative fantasies, and can have no other. Mine, by contrast, aims solely to make sense of the possibility of our a priori cognition of objects of experience. This problem has never yet been solved, or even raised. This brings down the whole of that fanciful idealism. It always inferred from our a priori cognitions, even those of geometry, a different kind of intuition from sensory intuition, namely intellectual intuition. We can already see this in Plato. No one ever thought that the senses might also intuit a priori.

376.1. The reviewer is mostly fighting his own shadow. When I contrast the truth of experience with dreams, he never thinks that I am referring only to the familiar “dream taken objectively” of Wolffian philosophy. This is purely formal. It pays no attention at all to the distinction between sleeping and waking, nor can it do so in a transcendental philosophy. He also calls my deduction of the categories and my table of the principles of the understanding “commonly known principles of logic and ontology, expressed in an idealistic manner.” Readers need only look up these points in the Prolegomena to convince themselves that no more wretched judgment, or one more historically incorrect, could possibly be made.