Preface to the Second Edition

B vii Preface to the Second Edition

Whether the cultivation of the cognitions that belong to reason’s business follows the secure course of a science can soon be judged by its results. If, after much preparation and equipment, it comes to a standstill as soon as it approaches its goal, or must repeatedly retrace its steps and strike out on another path to reach it; likewise, if its various collaborators cannot be brought to agree on how their common purpose is to be pursued, then we may always be certain that such a study has by no means yet entered upon the secure course of a science, but is merely groping about. It is already a service to reason to discover this path, if possible, even if much that was included in the goal previously adopted without reflection must be abandoned as futile.

B viii That logic has followed this secure course since the earliest times is evident from the fact that, since Aristotle, it has not had to take a single step backward—unless we choose to count the removal of a few dispensable subtleties, or the clearer determination of what it teaches, as improvements, though these concern the elegance rather than the security of the science. It is also remarkable that, up to now, logic has been unable to take a single step forward, and thus seems to all appearances to be closed and complete. For when some modern thinkers imagined they were enlarging it by inserting psychological chapters on the various cognitive powers (imagination, wit), metaphysical chapters on the origin of cognition or the different kinds of certainty according to the difference of objects (idealism, skepticism, and so on), or anthropological chapters on prejudices (their causes and remedies), this arose from their ignorance of the distinctive nature of this science. It is not an enlargement but a disfigurement of the sciences when their boundaries are allowed to run into one another. The boundary of logic, however, is determined with complete precision by its being a science.

B ix That science does nothing but set out in full, and rigorously prove, the formal rules of all thinking—whether thinking is a priori or empirical, whatever its origin or object, and whatever contingent or natural obstacles it encounters in our mind.

Logic owes its success solely to its restricted scope, which entitles it, indeed obliges it, to abstract from all objects of cognition and their differences, so that in logic the understanding deals with nothing but itself and its form. Naturally, it must have been far more difficult for reason to enter upon the secure path of science when it has to do not merely with itself but also with objects. Hence logic, as a propaedeutic, constitutes, so to speak, only the forecourt of the sciences; and where items of knowledge are at issue, although a logic is presupposed for judging them, their acquisition must be sought in the sciences properly and objectively so called.

Now, insofar as reason is to be present in these sciences, something in them must be cognized a priori. Reason’s cognition can be related to its object in one of two ways.

B x Either it merely determines the object and its concept (which must be given from elsewhere), or it also makes the object actual. The first is theoretical, the second practical cognition of reason. In both, the pure part, however much or little it may contain—namely, the part in which reason determines its object wholly a priori—must first be presented on its own, without mixing into it what comes from other sources. For it is bad management to spend receipts blindly, without being able afterward, when the business runs into difficulties, to distinguish which part of the income can bear the expenditure and from which part it must be cut.

Mathematics and physics are the two theoretical cognitions of reason that are to determine their objects a priori: the former wholly purely, the latter at least in part purely, but also in accordance with sources of cognition other than reason.

From the earliest times to which the history of human reason extends, mathematics has followed the secure path of a science among that admirable people, the Greeks. Yet we must not suppose that it was as easy for mathematics as for logic, in which reason has to do only with itself, to find that royal road, or rather to open it for itself.

B xi I believe instead that mathematics long remained a mere groping about, especially among the Egyptians, and that this transformation must be attributed to a revolution brought about by the fortunate insight of a single person in an experiment. From that point on, the path to be taken could no longer be missed, and the secure course of a science was entered upon and marked out for all time and to infinite distances. The history of this revolution in the way of thinking, which was far more important than the discovery of the route around the famous cape, and of the fortunate person who brought it about, has not been preserved for us. Yet the story handed down to us by Diogenes Laertius, who names the supposed inventor of even the smallest elements of geometrical demonstration—elements that common judgment does not consider to need any proof—shows that the memory of the change brought about by the first trace of this new path’s discovery must have seemed exceedingly important to mathematicians and thus became unforgettable. A light dawned on the first person who demonstrated the equilateral triangle, whether his name was Thales or whatever else it may have been.

B xii For he found that he must not trace what he saw in the figure, or even its mere concept, and as it were learn its properties from that; rather, he must produce them through what he himself thought into it a priori according to concepts and presented through construction. He found that, to know anything securely a priori, he must attribute to the thing nothing but what followed necessarily from what he himself had put into it in accordance with his concept.

Natural science took much longer to find the highway of science, for it is only about a century and a half since the proposal of the ingenious Bacon of Verulam partly brought about this discovery and partly, since its trail had already been found, gave it fresh impetus. This discovery, too, can be explained by a sudden revolution in the way of thinking. Here I will consider natural science only insofar as it is founded on empirical principles.

When Galileo had his balls roll down an inclined plane with a weight he had himself chosen, or Torricelli had the air sustain a weight he had thought in advance to be equal to that of a column of water known to him, a light dawned on all investigators of nature.

B xiii The same happened when, still later, Stahl transformed metals into calx and this back into metal by taking something away from them and giving it back*. They understood that reason has insight only into what it itself produces according to its own plan; that it must lead the way with principles of its judgments according to constant laws and compel nature to answer its questions, rather than let itself be led by nature alone, as if on a leash. For otherwise accidental observations, made according to no previously devised plan, do not connect at all in a necessary law, which is nevertheless what reason seeks and needs. Reason must approach nature with its principles in one hand, according to which alone agreeing appearances can count as laws, and in the other the experiment it has devised in accordance with those principles. It must do so to be instructed by nature, certainly, but not as a pupil who lets the teacher dictate whatever the teacher wishes; rather, as an appointed judge who compels witnesses to answer the questions he puts to them. Thus even physics owes the very advantageous revolution in its way of thinking solely to a single idea.

B xiv That idea was to seek in nature, in accordance with what reason itself puts into it, what reason must learn from nature and could not know on its own—not to invent it and ascribe it to nature. Only through this was natural science first brought onto the secure course of a science, after having been nothing more than a mere groping about for so many centuries.

* Here I am not following precisely the historical course of the experimental method, whose first beginnings are not well known either.

Metaphysics, an entirely isolated speculative cognition of reason that rises wholly above instruction from experience, and does so through mere concepts—not, like mathematics, by applying them to intuition—has not yet enjoyed a fate so favorable that it could enter upon the secure course of a science. Here, then, reason is to be its own pupil. Yet metaphysics is older than all the other sciences and would remain even if all the rest were swallowed up entirely in the abyss of an all-destroying barbarism. For in metaphysics reason continually comes to a standstill, even when it wishes to gain a priori insight, as it claims to do, into laws confirmed by the most ordinary experience. In metaphysics we must retrace our path countless times because we find that it does not lead where we wish to go.

B xv As for agreement among its adherents in their assertions, metaphysics is still so far from this that it is instead a battlefield apparently designed expressly for exercising one’s powers in mock combat, where no fighter has ever been able to win even the smallest piece of ground and establish lasting possession on the strength of his victory. There is therefore no doubt that its procedure has so far been a mere groping about, and, worst of all, among mere concepts.

What is it, then, that has kept a secure path of science from being found here? Is it perhaps impossible? Why, then, has nature afflicted our reason with the restless striving to seek it out as one of its most important concerns? More than that, how little cause we have to place confidence in our reason if, in one of the most important objects of our curiosity, it not only abandons us but holds us off with false pretenses and finally deceives us! Or has the path merely been missed until now? What sign can we use to hope that, in a renewed search, we will be more fortunate than others before us?

Mathematics and natural science became what they now are through a revolution accomplished all at once.

B xvi I should think their example remarkable enough to prompt reflection on the essential feature of the change in their way of thinking that proved so advantageous to them, and to imitate them in this, at least as an experiment, so far as their analogy with metaphysics, as cognitions of reason, permits. Until now it has been assumed that all our cognition must conform to the objects; but all attempts to establish something about them a priori through concepts, by which our cognition would be enlarged, have come to nothing on this assumption. Let us therefore try for once whether we make better progress with the problems of metaphysics by assuming that the objects must conform to our cognition. This already agrees better with the desired possibility of a cognition of objects a priori, a cognition that is to establish something about objects before they are given to us. The situation here is like that of Copernicus’s first thoughts. When he could make no good progress in explaining the movements of the heavens on the assumption that the entire host of stars revolved around the spectator, he tried whether he might succeed better by having the spectator revolve while leaving the stars at rest.

B xvii In metaphysics we can make a similar experiment concerning the intuition of objects. If intuition had to conform to the constitution of the objects, I do not see how we could know anything about it a priori. But if the object, as an object of the senses, conforms to the constitution of our faculty of intuition, I can quite well represent this possibility to myself. Yet I cannot stop at these intuitions if they are to become cognitions; I must refer them, as representations, to something as their object and determine that object through them. I can therefore either assume that the concepts through which I bring about this determination also conform to the object, and then I am once again in the same difficulty as to how I could know anything about it a priori; or I assume that the objects—or, what amounts to the same thing, the experience in which alone they are cognized as given objects—conform to these concepts. I then see at once an easier solution. For experience is itself a kind of cognition that requires understanding, whose rule I must presuppose in myself before objects are given to me, hence a priori. This rule is expressed in a priori concepts. All objects of experience must therefore necessarily conform to these concepts and agree with them.

B xviii As for objects insofar as they are thought merely through reason, and indeed necessarily, but cannot be given in experience at all—at least not as reason thinks them—the attempts to think them, for they must surely allow themselves to be thought, will afterward provide a splendid touchstone for what we are adopting as the changed method in our way of thinking: namely, that we cognize a priori of things only what we ourselves put into them.*

* This method, modeled on that of the investigator of nature, thus consists in seeking the elements of pure reason in what can be confirmed or refuted by an experiment. Now, to test propositions of pure reason, especially when they venture beyond every boundary of possible experience, no experiment can be made with their objects, as it can in natural science. An experiment will therefore be practicable only with concepts and principles that we assume a priori: we arrange them so that the same objects can be considered from two different sides—on the one hand as objects of the senses and the understanding for experience, and on the other as objects merely thought, if need be for reason isolated and striving beyond the boundary of experience. If it now turns out that, when things are considered from this twofold standpoint, agreement with the principle of pure reason is found, whereas from a single standpoint an unavoidable conflict of reason with itself arises, the experiment decides in favor of the correctness of that distinction.

This experiment succeeds as desired and promises metaphysics the secure course of a science in its first part, where it deals with a priori concepts for which the corresponding objects can be given in experience in conformity with them.

B xix For after this change in our way of thinking, we can quite well explain the possibility of a priori cognition and, what is more, supply satisfactory proofs of the laws that lie a priori at the foundation of nature as the sum total of the objects of experience. Both were impossible under the previous procedure. But from this deduction of our capacity to cognize a priori there emerges, in the first part of metaphysics, a strange result, apparently very detrimental to its entire purpose, with which the second part is concerned: namely, that with this capacity we can never go beyond the boundary of possible experience, though precisely this is the most essential concern of this science.

B xx Yet here lies the experiment that provides a countercheck on the truth of the result of that first assessment of our a priori rational cognition: that it extends only to appearances, leaving the thing in itself as indeed actual in itself but uncognized by us. For what necessarily drives us beyond the boundary of experience and of all appearances is the unconditioned, which reason necessarily and with every right demands in things in themselves for everything conditioned, thereby demanding the series of conditions as complete. Now, suppose we find that, on the assumption that our cognition through experience conforms to objects as things in themselves, the unconditioned cannot be thought at all without contradiction; but that, on the assumption that our representation of things as they are given to us does not conform to them as things in themselves, and that these objects as appearances instead conform to our way of representing, the contradiction disappears; and that consequently the unconditioned must be encountered not in things insofar as we know them, as they are given to us, but in them insofar as we do not know them, as things in themselves.

B xxi Then it becomes clear that what we initially assumed only as an experiment is well grounded.* Now, after speculative reason has been denied all progress in this field of the supersensible, we still have to try whether data for determining that transcendent concept of reason, the concept of the unconditioned, may not be found in its practical cognition. In this way we may, in accordance with the wish of metaphysics, reach beyond the boundary of all possible experience with our a priori cognition, though such cognition is possible only for practical purposes. And by proceeding in this way, speculative reason has at least made room for such an enlargement, even if it had to leave that room empty. We therefore remain free—indeed, speculative reason itself calls on us—to fill that room.

B xxii We are to do so, if we can, with practical data of reason.∗∗

* This experiment of pure reason has much in common with the chemists’ experiment, which they sometimes call the experiment of reduction, but generally the synthetic procedure. The metaphysician’s analysis separated pure a priori cognition into two very dissimilar elements: cognition of things as appearances and cognition of things in themselves. Dialectic reunites the two in agreement with the necessary rational idea of the unconditioned, and finds that this agreement can never be achieved except through that distinction, which is therefore the true one.

∗∗ In the same way, the central laws of the motion of heavenly bodies gave established certainty to what Copernicus had at first assumed only as a hypothesis. At the same time they proved the invisible force binding the structure of the universe together—Newtonian attraction—which would have remained forever undiscovered had Copernicus not ventured, in a manner contrary to the senses yet true, to seek the observed movements not in the objects of the heavens but in their spectator. In this preface I likewise present the change in the way of thinking set out in the Critique, analogous to that hypothesis, only as a hypothesis. In the treatise itself, however, it is proved not hypothetically but apodictically from the constitution of our representations of space and time and from the elementary concepts of the understanding. My purpose here is only to draw attention to the first attempts at such a change, which are always hypothetical.

The business of this critique of pure speculative reason consists in that attempt to change the procedure hitherto followed by metaphysics, by carrying out a complete revolution in it after the example of geometers and investigators of nature. It is a treatise on method, not a system of the science itself; yet it traces the science’s entire outline, both as regards its boundaries and its whole internal structure.

B xxiii For pure speculative reason has this peculiarity: it can and should measure its own capacity according to the different ways in which it selects objects for thought, and itself enumerate completely the various ways of setting itself problems, thus sketching the entire plan for a system of metaphysics. As regards the first point, this is because in a priori cognition nothing can be attributed to objects except what the thinking subject draws from itself. As regards the second, it is because reason, with respect to its principles of cognition, is an entirely separate, self-subsisting unity in which, as in an organized body, every member exists for the sake of all the others and all for the sake of each. No principle can be taken with assurance in one relation without having been investigated at the same time in its thoroughgoing relation to the entire pure use of reason. In return, metaphysics also enjoys a rare good fortune that can belong to no other science of reason concerned with objects—for logic deals only with the form of thinking in general. The good fortune is this: once this critique has brought metaphysics onto the secure course of a science, it can embrace the whole field of cognitions belonging to it. It can thus complete its work and leave it for posterity’s use as a capital fund that can never be increased.

B xxiv For it deals only with principles and with the limitations of their use, which are determined by those principles themselves. As a fundamental science, it is therefore also bound to this completeness, and it must be possible to say of it: nil actum reputans, si quid superesset agendum (“he counts nothing done while anything remains to be done”).

But what, someone will ask, is the treasure we intend to leave to posterity in a metaphysics purified in this way by critique and thereby also brought into a lasting condition? A cursory survey of this work may seem to show that its benefit is merely negative: that we must never venture with speculative reason beyond the boundary of experience. And this is indeed its first benefit. But this benefit at once becomes positive when we recognize that the principles with which speculative reason ventures beyond its boundary in fact lead inevitably not to an enlargement but, on closer examination, to a restriction of our use of reason. For they actually threaten to extend the boundaries of sensibility, to which they properly belong, over everything.

B xxv They thus threaten to displace the pure (practical) use of reason altogether. Hence a critique that limits speculative reason is indeed negative in that respect; but by at the same time removing an obstacle that restricts the latter use, or even threatens to destroy it, it has in fact a positive and very important benefit. This becomes clear as soon as we are convinced that there is an absolutely necessary practical use of pure reason—the moral use—in which reason inevitably extends beyond the boundaries of sensibility. For this it needs no assistance from speculative reason, but must nevertheless be secured against its opposition, so as not to fall into contradiction with itself. To deny this service of critique a positive benefit would be like saying that the police confer no positive benefit because their principal business is merely to put a stop to the violence citizens may fear from other citizens, so that each can pursue his affairs in peace and security. The analytic part of the Critique proves that space and time are only forms of sensible intuition, hence only conditions of the existence of things as appearances; further, that we have no concepts of the understanding, and thus no elements for cognizing things at all.

B xxvi It proves that we have them only insofar as an intuition corresponding to these concepts can be given, and consequently that we can have cognition of no object as a thing in itself, but only insofar as it is an object of sensible intuition, that is, as an appearance. From this, of course, follows the restriction of all possible speculative cognition of reason to mere objects of experience. Yet—and this must be carefully noted—it is always reserved that, although we cannot cognize these same objects as things in themselves, we must at least be able to think them as such*. Otherwise the absurd proposition would follow that there is an appearance without anything that appears.

B xxvii Now let us assume that the distinction made necessary by our critique between things as objects of experience and those same things as things in themselves had not been made at all. Then the principle of causality, and hence the mechanism of nature in determining them, would have to hold without exception for all things in general as efficient causes. Of one and the same being, for example the human soul, I could therefore not say that its will is free and yet at the same time subject to natural necessity, that is, not free, without falling into an obvious contradiction. For in both propositions I would have taken the soul in precisely the same sense, namely as a thing in general (as a thing in itself), and without a prior critique could not have taken it otherwise. But suppose the critique has not erred in teaching us to take the object in two senses, namely as appearance or as thing in itself; suppose its deduction of the concepts of the understanding is correct, and hence the principle of causality applies only to things taken in the first sense, insofar as they are objects of experience, while those very same things in the second sense are not subject to it.

B xxviii Then the very same will is thought, in appearance—in its visible actions—as necessarily conforming to the law of nature and to that extent not free, and yet, on the other hand, as belonging to a thing in itself, as not subject to that law and thus as free, without any contradiction arising. Now, although I cannot cognize my soul, considered from the latter side, through any speculative reason, still less through empirical observation, and therefore also cannot cognize freedom as a property of a being to which I ascribe effects in the sensible world—because I would have to cognize such a being as determined in its existence and yet not in time (which is impossible, since I cannot supply my concept with an intuition)—I can nevertheless think freedom. That is, its representation at least contains no contradiction in itself, provided our critical distinction between the two ways of representing, the sensible and the intellectual, is valid, together with the resulting limitation of the pure concepts of the understanding and hence also of the principles flowing from them. Now suppose morality necessarily presupposes freedom, in the strictest sense, as a property of our will, adducing, as its data a priori, original practical principles lying in our reason.

B xxix Without the presupposition of freedom these principles would be absolutely impossible; but suppose speculative reason had proved that freedom cannot be thought at all. Then the former presupposition, the moral one, would necessarily have to yield to the one whose opposite contains an obvious contradiction. Consequently freedom, and with it morality—for morality’s opposite contains no contradiction unless freedom is already presupposed—would have to give way to the mechanism of nature. As matters stand, however, for morality I need nothing more than that freedom does not contradict itself, and can thus at least be thought, without my needing any further insight into it; and that it therefore places no obstacle in the way of the natural mechanism of the very same action, taken in another relation. Thus the doctrine of morality keeps its place, and the doctrine of nature keeps its own. This could not have happened had critique not first instructed us about our unavoidable ignorance concerning things in themselves and restricted everything we can cognize theoretically to mere appearances. The same exposition of the positive benefit of the critical principles of pure reason can be given with regard to the concept of God and the simple nature of our soul, but for brevity I pass over it.

B xxx I cannot, therefore, even assume God, freedom, and immortality for the sake of the necessary practical use of my reason unless I at the same time deprive speculative reason of its pretension to extravagant insights. For, to attain these, it must employ principles that in fact extend only to objects of possible experience; when these are nevertheless applied to what cannot be an object of experience, they always actually transform it into appearance and thus declare every practical enlargement of pure reason impossible. I therefore had to set aside knowledge to make room for belief; and the dogmatism of metaphysics—that is, the prejudice that we can make progress in it without a critique of pure reason—is the true source of all unbelief opposed to morality, which is always highly dogmatic.—If, then, it can be no great difficulty to leave posterity a legacy in a systematic metaphysics composed according to the critique of pure reason, this is no gift to be slighted. We may look merely to the cultivation of reason through the secure course of a science in general.

B xxxi This is to be compared with its groundless groping and reckless wandering without critique. Or we may look to the better use of time by inquisitive young people, who under ordinary dogmatism receive so early and so much encouragement to reason idly about things they do not understand, and into which neither they nor anyone in the world will ever gain insight, or even to set out to invent new thoughts and opinions, and so neglect the learning of well-grounded sciences. Above all, however, we may reckon the priceless advantage of putting an end for all future time to every objection against morality and religion in the Socratic manner: by the clearest proof of the opponents’ ignorance. For some metaphysics has always existed in the world and will presumably continue to exist; and with it a dialectic of pure reason will also be found, since this is natural to reason. It is therefore philosophy’s first and most important concern to deprive this dialectic of all harmful influence once and for all by stopping up the source of its errors.

* To cognize an object, I must be able to prove its possibility, either from its actuality as attested by experience or a priori through reason. But I can think whatever I please, provided I do not contradict myself—that is, provided my concept is a possible thought—even though I cannot guarantee whether an object corresponds to it within the sum total of all possibilities. To ascribe objective validity to such a concept, however—real possibility, since the former was merely logical—something more is required. But this something more need not be sought in theoretical sources of cognition; it may also lie in practical ones.

Despite this important change in the field of the sciences, and the loss speculative reason must suffer in its hitherto imagined possessions, everything remains in the same advantageous condition as ever with regard to the universal human concern and the benefit the world has until now drawn from the teachings of pure reason.

B xxxii The loss affects only the monopoly of the schools, by no means the interest of humanity. I ask the most unbending dogmatist whether the proof of our soul’s continued existence after death from the simplicity of substance; the proof of freedom of the will against universal mechanism through the subtle but powerless distinctions between subjective and objective practical necessity; or the proof of God’s existence from the concept of a most real being, from the contingency of what changes and the necessity of a first mover—whether, after issuing from the schools, these proofs have ever been able to reach the public and exert the slightest influence on its conviction. If this has not happened, and can never be expected, given the ordinary human understanding’s unsuitability for such subtle speculation, then rather, in the first case, the disposition of our nature, evident to everyone, never to be satisfied by temporal things (as inadequate to the capacities for our whole vocation), must alone have produced the hope of a future life.

B xxxiii In the second, the mere clear presentation of duties in opposition to every claim of inclination must alone have produced the consciousness of freedom. And finally, in the third, the magnificent order, beauty, and care that shine forth everywhere in nature must alone have produced belief in a wise and great author of the world. If these alone must have brought about the conviction that spreads among the public, insofar as it rests on rational grounds, then this possession not only remains undisturbed but gains in authority. For the schools are now taught to claim no higher or more extensive insight, on a point of universal human concern, than that which the great multitude, most worthy of our respect, can reach just as easily. They are thus taught to restrict themselves solely to cultivating these grounds of proof, which are universally accessible and sufficient for moral purposes. The change therefore concerns only the arrogant claims of the schools, which would gladly have themselves regarded here—as they rightly are in many other matters—as the sole experts and custodians of truths whose use alone they communicate to the public, keeping the key to themselves (quod mecum nescit, solus vult scire videri).

B xxxiv Nevertheless, provision is also made for a more reasonable claim of the speculative philosopher. He always remains the exclusive trustee of a science useful to the public without its knowing it: the critique of reason. For this can never become popular, nor need it do so. Just as the finely spun arguments for useful truths do not enter the people’s heads, so the equally subtle objections against them never occur to them either. The schools, by contrast, like everyone who rises to speculation, inevitably encounter both. They are therefore bound, by a thorough investigation of the rights of speculative reason, to prevent once and for all the scandal that sooner or later must arise even among the people from the disputes into which metaphysicians—and, as such, eventually even clergymen—inevitably become entangled without critique, and which afterward falsify even their doctrines. Only through critique can the very roots be cut away from materialism, fatalism, atheism, freethinking unbelief, fanaticism, and superstition, which can become harmful to everyone, and finally also from idealism and skepticism, which are more dangerous to the schools and can hardly spread to the public.

B xxxv If governments see fit to concern themselves with the affairs of scholars at all, it would be far more consistent with their wise care for the sciences and for humanity to favor the freedom of such a critique, through which alone the labors of reason can be placed on a firm footing, than to support the ridiculous despotism of the schools. These raise a loud outcry about public danger whenever their cobwebs are torn, though the public has never taken notice of them and can therefore never feel their loss.

Critique is not opposed to reason’s dogmatic procedure in its pure cognition as science—for science must always be dogmatic, that is, prove rigorously from secure a priori principles—but to dogmatism: the presumption of getting on by itself with a pure cognition from concepts (the philosophical), according to principles such as reason has long employed, without inquiring how and by what right it arrived at them. Dogmatism is therefore the dogmatic procedure of pure reason without a preceding critique of its own capacity. This opposition is not meant to speak in favor of a chattering shallowness under the pretended name of popularity.

B xxxvi Still less is it meant to speak for skepticism, which makes short work of all metaphysics. Rather, critique is the necessary preliminary preparation for advancing a well-grounded metaphysics as science. This must necessarily be carried out dogmatically and, by the strictest requirement, systematically, hence in a scholarly, not a popular, manner. For this demand upon it is indispensable, since it undertakes to carry out its business wholly a priori and thus to the full satisfaction of speculative reason. In carrying out the plan prescribed by the Critique, that is, in the future system of metaphysics, we must therefore one day follow the rigorous method of the celebrated Wolf, the greatest of all dogmatic philosophers. He first gave the example—and through this example became the originator of the spirit of thoroughness in Germany, which has not yet died out—of how to enter upon the secure course of a science by establishing principles in accordance with rules, clearly determining concepts, attempting rigorous proofs, and preventing bold leaps in inferences. For that very reason he was especially well suited to place a science such as metaphysics in this condition, had it occurred to him first to prepare the field through a critique of its organ, pure reason itself.

B xxxvii This lack is to be attributed less to him than to the dogmatic way of thinking of his age; on this score, the philosophers of his time and of all preceding times have nothing to reproach one another for. Those who reject both his method of teaching and the procedure of the critique of pure reason can have no other intention than to throw off the bonds of science altogether, to turn labor into play, certainty into opinion, and philosophy into a love of opinion.

As for this second edition, I have, as was only right, not wished to let the opportunity pass without remedying, as far as possible, the difficulties and obscurity that may have given rise to some of the misinterpretations acute thinkers have encountered in judging this book, perhaps not without fault on my part. In the propositions themselves and their grounds of proof, as also in the form and completeness of the plan, I have found nothing to change. This is attributable partly to the long examination to which I subjected them before presenting the book to the public, and partly to the nature of the matter itself: the nature of a pure speculative reason, which contains a genuine articulated structure in which everything is an organ, everything existing for the sake of one and each individual part for the sake of all.

B xxxviii Hence any infirmity, however small, whether a fault (an error) or a deficiency, must inevitably betray itself in use. I hope this system will continue to maintain itself in this unchangeability. It is not conceit that entitles me to this confidence, but merely the evidence produced by the experiment of obtaining the same result both in proceeding from the smallest elements to the whole of pure reason and in returning from the whole—which is also given independently through reason’s ultimate practical purpose—to each part. For the attempt to change even the smallest part immediately produces contradictions, not merely within the system but within universal human reason. Yet much remains to be done in the presentation, and in this edition I have attempted improvements intended to remedy, in part, the misunderstanding of the Aesthetic, especially of the concept of time; in part, the obscurity of the deduction of the concepts of the understanding; in part, the supposed lack of sufficient evidence in the proofs of the principles of the pure understanding; and finally, the misinterpretation of the paralogisms charged against rational psychology.

B xxxix Thus far—that is, only to the end of the first chapter of the Transcendental Dialectic, and no further—do my changes to the manner of presentation* extend.

B xl This is because time was too short.

B xli It is also because, concerning the rest, no misunderstanding on the part of competent and impartial examiners had come to my attention.

B xlii Even without my being permitted to name them with the praise they deserve, they will find for themselves, in the appropriate places, the attention I have paid to their observations. But this improvement entails a small loss for the reader, which could not be avoided without making the book far too voluminous. Various things that are not essential to the completeness of the whole, but that some readers might nevertheless be sorry to miss, since they can be useful for other purposes, have had to be omitted or presented in an abbreviated form to make room for what I hope is now a more intelligible presentation. Fundamentally, this changes absolutely nothing in the propositions or even in their grounds of proof; yet in places its method of exposition departs so far from the earlier one that it could not be accomplished by insertions. I hope the greater intelligibility more than compensates for this small loss, which in any case can be made good by comparing the first edition, as each reader pleases. In various published writings, partly on the occasion of reviews of books and partly in separate treatises, I have observed with grateful pleasure that the spirit of thoroughness has not died out in Germany, but has only been drowned out for a short time by the fashionable tone of a genius-like freedom in thinking.

B xliii I have also observed that the thorny paths of critique, which lead to a scholarly science of pure reason—yet one that is lasting only as such, and therefore supremely necessary—have not prevented courageous and clear minds from mastering it. To these deserving men, who so happily combine thorough insight with a talent for lucid presentation, of which I am not particularly conscious in myself, I leave the completion of my work wherever it may still be deficient in the latter respect. For in this case the danger is not of being refuted, but of not being understood. For my part, I cannot henceforth enter into disputes, though I will carefully attend to every suggestion, whether from friends or opponents, in order to use them in the future elaboration of the system in accordance with this propaedeutic. Since in the course of this work I have already advanced rather far into old age—entering my sixty-fourth year this month—I must be sparing with my time if I am to carry out my plan of providing the metaphysics of nature and of morals as confirmation of the correctness of the critique of both speculative and practical reason.

B xliv The clarification of obscurities scarcely avoidable at first in this work, and the defense of the whole, I must expect from the deserving men who have made it their own. Every philosophical exposition can be pinched at individual points, for it cannot appear in armor as a mathematical one can. Yet the articulated structure of the system, considered as a unity, does not thereby run the slightest risk. When a system is new, few possess the mental agility to survey it, and still fewer the inclination, since every innovation is unwelcome to them. Apparent contradictions, too, can be picked out of any writing, especially one proceeding in the manner of free discourse, if individual passages are torn from their context and compared with one another. In the eyes of those who rely on others’ judgment, these cast an unfavorable light on the work; but for anyone who has grasped the idea as a whole, they are very easily resolved. Meanwhile, if a theory has stability within itself, the action and reaction that at first threatened it with great danger serve over time only to smooth its unevenness and, if men of impartiality, insight, and true popularity devote themselves to it, to give it soon the requisite elegance as well.

Königsberg, April 1787.

* The only addition I could call a genuine enlargement, though only in the manner of proof, is the new refutation of psychological idealism and the rigorous proof—as I believe, the only possible one—of the objective reality of outer intuition that I have given on p. 273. However harmless idealism may be held to be in relation to the essential purposes of metaphysics, which in fact it is not, it always remains a scandal to philosophy and universal human reason that we must accept the existence of things outside us merely on faith, (from which, after all, we have the entire material for cognitions, even for our inner sense), and that, if anyone chooses to doubt it, we cannot oppose him with a satisfactory proof. Since there is some obscurity in the wording of the proof from the third line to the sixth, I ask that the sentence be changed as follows: “But this persistent element cannot be an intuition within me. For all the determining grounds of my existence that can be encountered within me are representations, and as such themselves require a persistent element distinct from them, in relation to which their change, and thus my existence in the time in which they change, can be determined.” Someone will presumably say against this proof: I am, after all, immediately conscious only of what is within me, that is, of my representation of outer things; consequently, it still remains undecided whether anything outside me corresponds to it or not. But I am conscious of my existence in time, and hence also of its determinability in time, through inner experience. This is more than being merely conscious of my representation, yet is identical with the empirical consciousness of my existence, which is determinable only through relation to something that is outside me and bound up with my existence. This consciousness of my existence in time is thus inseparably combined, as one and the same consciousness, with the consciousness of a relation to something outside me. It is therefore experience, not invention, sense, not imagination, that inseparably connects what is outer with my inner sense. For outer sense is already in itself a relation of intuition to something actual outside me, and its reality, as distinct from imagining, rests only on its being inseparably combined with inner experience itself as the condition of the latter’s possibility, which is what happens here. If, along with the intellectual consciousness of my existence in the representation “I am,” which accompanies all my judgments and acts of understanding, I could also combine a determination of my existence through intellectual intuition, then consciousness of a relation to something outside me would not necessarily belong to that determination. But although that intellectual consciousness precedes, the inner intuition in which alone my existence can be determined is sensible and bound to the condition of time. This determination, and hence inner experience itself, depends on something persistent that is not within me, and thus only on something outside me in relation to which I must consider myself. The reality of outer sense is therefore necessarily combined with that of inner sense for the possibility of experience in general. That is, I am just as securely conscious that there are things outside me relating to my sense as I am conscious that I myself exist as determined in time. But which given intuitions actually have objects outside me corresponding to them, and thus belong to outer sense and are to be ascribed to it rather than to imagination, must be decided in each particular case according to the rules by which experience in general, even inner experience, is distinguished from imagining. The proposition that there actually is outer experience always lies at the foundation of this. One may add the following observation: the representation of something persistent in existence is not the same as a persistent representation. For this representation can be very mutable and changing, like all our representations, even those of matter, and yet relate to something persistent. That persistent something must therefore be a thing distinct from all my representations and external to them, whose existence is necessarily included in the determination of my own existence and, together with it, constitutes one single experience, which would not even occur inwardly if it were not at the same time partly outward. The question of how this happens admits of no further explanation here, any more than how we think at all of what stands still in time, whose simultaneity with what changes produces the concept of alteration.

B vii Preface to the Second Edition

You can soon tell from the results whether work on the cognitions that belong to reason’s business is taking the secure path of a science. Suppose a study makes many arrangements and preparations, but gets stuck as soon as it comes to its goal. Or suppose it often has to go back and take another road to reach that goal. Or suppose the people working on it can’t agree among themselves on how to go after their shared aim. In any of these cases you can be sure that the study is still far from the secure path of a science. It is only groping around. Finding that path, if it can be found, already does reason a service. That holds even if some things have to be dropped as futile that were part of the aim adopted earlier without much thought.

B viii Logic has gone down this secure path since the earliest times. You can see it from the fact that it hasn’t had to take one step backward since Aristotle. (The exception would be if you counted as improvements the removal of a few needless subtleties or a clearer statement of what it teaches. But those have more to do with the elegance of the science than with its security.) What is also remarkable about logic is that, up to now, it hasn’t been able to take a single step forward either. By all appearances it is closed and complete. Some recent writers did think they could enlarge it. They pushed in some psychology, with chapters on the various powers of cognition (imagination, wit). They pushed in some metaphysics: chapters on where cognition comes from, or on how certainty varies with the kind of object (idealism, skepticism and the like). And they pushed in some anthropology: chapters on prejudices, with their causes and the cures for them. All of this comes from not knowing the special nature of this science. When you let the boundaries of sciences run into each other, you don’t enlarge them. You deform them. The boundary of logic is fixed quite exactly by what kind of science it is.

B ix All it does is lay out in full the formal rules of all thinking, and prove them rigorously. Those rules hold for any thinking at all, whether a priori or empirical, from any source and about anything, and whether it meets accidental or natural obstacles in our mind.

Logic owes its success only to its narrow scope. That scope entitles it, in fact obliges it, to set aside all objects of cognition and the differences between them. So in logic the understanding has nothing to deal with except itself and its form. It was naturally much harder for reason to find the secure path of a science when it has to deal not just with itself but with objects too. That is why logic, as a preliminary discipline, makes up only the forecourt of the sciences, so to speak. When we’re talking about bodies of knowledge, we do presuppose a logic for judging them. But their acquisition has to be sought in those sciences that are properly and objectively so called.

If these sciences are to involve reason, they have to contain something cognized a priori. Reason’s cognition can relate to its object in two ways. One way is simply to fix the object and its concept (which has to be given from somewhere else).

B x The other is to make the object actual as well. The first is theoretical cognition of reason, the second practical. In each of the two, the pure part has to be presented first and on its own. This is the part where reason fixes its object wholly a priori, however much or little there is of it. What comes from other sources must not be mixed in with it. Otherwise the household is badly run. You spend whatever comes in without looking. Then, when the money runs short, you can’t tell which part of the income can cover the spending, and which part of the spending you have to cut.

Reason has two theoretical cognitions whose job is to determine their objects a priori. They are mathematics and physics. Mathematics does so in entirely pure form. Physics does so at least partly in pure form, and beyond that by way of sources of cognition other than reason.

Mathematics took the secure path of a science from the earliest times that the history of human reason reaches, among the admirable people of the Greeks. But don’t think that mathematics had it as easy as logic, where reason deals only with itself. Hitting on that royal road was harder for mathematics.

B xi Or rather, it had to build that road for itself. I believe it kept groping around for a long time, especially among the Egyptians. And I think this change should be credited to a revolution. One lucky idea of a single man, in a single experiment, brought it about. After that nobody could miss the road that had to be taken, and a science’s secure course was set out and mapped for all time, reaching into endless distances. That revolution in the way of thinking mattered much more than finding the way around the famous cape. But the history of that revolution hasn’t been preserved for us, and neither has the story of the lucky man who brought it about. Still, there is the story told by Diogenes Laertius. He names the supposed discoverer of even the smallest elements of geometrical demonstrations, elements that ordinary judgment thinks need no proof at all. The story shows that mathematicians must have found the memory of the change extremely important, the change set off by the first glimpse of this new road. That is what made it unforgettable. A light dawned on the first man to demonstrate the equilateral triangle (call him Thales, or whatever name you like).

B xii That was because he found that he must not go looking in the figure as he saw it, or in the bare concept of the figure, and so to speak learn its properties from there. He had to bring them out by what he himself had thought into the figure a priori, according to concepts, and presented in it (by construction). And to know something a priori for certain, he could credit the thing with nothing beyond what must follow from whatever he had himself put into it through his concept.

Natural science took far longer to reach the main highway of science. That is because it was only about a century and a half ago that the proposal of that clever man, Bacon of Verulam, helped bring on this discovery. It also gave the discovery more life, because people were already on its track. This too can be explained by a quick revolution in the way of thinking. Here I’ll look only at natural science so far as it is founded on empirical principles.

Galileo let balls of a weight he had picked himself roll down a slope. Torricelli made the air carry a weight that he had thought beforehand to be equal to a column of water he knew. Later still, Stahl turned metals into calx.

B xiii He changed the calx into metal again by removing something from the metals and returning it*. Then a light dawned on all investigators of nature. They understood this: reason can see into only those things that it brings forth itself on a plan of its own. It must go ahead with the principles of its judgments, which follow constant laws, and force nature to answer its questions. It must not just let nature lead it around on a string, so to speak. Otherwise accidental observations, made on no plan drawn up beforehand, don’t connect up in any necessary law, and that is exactly what reason is looking for and needs. Reason must go up to nature holding its principles in one hand (these are the only thing that lets agreeing appearances pass as laws). In its other hand it must hold the experiment it has devised on their basis. It goes to learn from nature, certainly. But it doesn’t go like a pupil who just repeats whatever the teacher wants said. It goes like an appointed judge who makes the witnesses answer the questions put to them. So even physics owes its fortunate revolution in thinking to one idea alone.

B xiv The idea is to be guided by what reason itself puts into nature, and in that light to look in nature (not to invent it and hand it to nature) for what reason has to learn from nature and could never know by itself. Only this brought natural science onto the secure path of a science, after it had been nothing more than groping around for so many centuries.

* I’m not following the thread of the history of the experimental method exactly here. Its first beginnings aren’t well known either.

Metaphysics is a wholly isolated kind of speculative cognition of reason. It rises completely above what experience can teach, and it does this through concepts alone. Unlike mathematics, it doesn’t apply concepts to intuition. Here reason is supposed to be its own pupil. So far, fate hasn’t been kind enough to let metaphysics take the secure path of a science. And yet it is older than all the other sciences. It would remain even if all the others were swallowed up together in the abyss of an all-destroying barbarism. That is because reason constantly gets stuck in metaphysics, even when it wants to see a priori (as it presumes it can) the laws that the most ordinary experience confirms. In metaphysics you have to go back over the road countless times, because you find it doesn’t lead where you want to go.

B xv As for agreement among its followers in what they assert, metaphysics is so far from it that it is rather a battlefield. It seems to have been designed for exercising one’s strength in mock combat. On it no fighter has ever won even the smallest piece of ground, or built a lasting possession on that victory. So there is no doubt that its procedure has been nothing but groping around so far, and what is worst, groping among mere concepts.

So why hasn’t a secure scientific path been found here yet? Is it perhaps impossible? Then why did nature plague our reason with a restless drive to hunt for this path as one of its most important concerns? And there’s more. How little cause we have to put our trust in reason, when it fails us in one of the weightiest matters we’re curious about! It doesn’t just fail us. It strings us along with false promises and finally cheats us. Or has the path only been missed so far? Then what sign is there that we could use to hope for better luck than others had before us, if we search again?

I’d say the examples of mathematics and natural science, which became what they are now through a revolution brought about all at once, are remarkable enough.

B xvi That should make us think about the essential part of the change in thinking that did them so much good. And we should try imitating them in this respect, at least as an experiment, as far as their likeness to metaphysics, as cognitions of reason, allows. People have so far assumed that our cognition, all of it, has to conform to objects. But on that assumption, every attempt to establish something about objects a priori through concepts, something that would extend our cognition, came to nothing. So let’s try, for once, whether we get on better with the tasks of metaphysics if we assume that objects have to conform to our cognition. That agrees better with the demanded possibility of a priori cognition of objects, which is supposed to settle something about objects before they are given to us. It’s the same as with the first thoughts of Copernicus. He wasn’t getting far in explaining the motions of the heavens, so long as he assumed that the whole host of stars revolved around the spectator. So he tried whether he would do better by making the spectator revolve and leaving the stars at rest.

B xvii In metaphysics we can try something similar with the intuition of objects. If intuition had to conform to the nature of objects, I don’t see how anyone could know anything of it a priori. But if it’s the object (considered as an object of the senses) that fits itself to how our faculty of intuition is built, then I can picture that possibility very well. Still, if these intuitions are to become cognitions, I can’t leave it at that. I have to relate them, as representations, to something that serves as their object, and use them to determine that object. So there are two options. First, I could assume that the concepts by which I carry out this determination also conform to the object. Then I’m in the same difficulty again about how I could know anything about the object a priori. Second, I could assume that objects conform to these concepts—or, to say the same thing, that experience does, since experience is the only place where objects are cognized as given. Then I see an easier way out at once, because experience itself is a kind of cognition that requires understanding. I have to presuppose the understanding’s rule in myself before any objects are given to me, and so a priori. That rule is expressed in a priori concepts.

B xviii So all objects of experience must necessarily conform to these concepts and agree with them. As for objects that reason alone thinks, and thinks as necessary, though experience can’t supply them at all (not, at any rate, in the way reason thinks them): our attempts to think them—and think them we must—will afterward provide an excellent touchstone for what we adopt as the changed method of thinking. The method is this: the only thing we cognize a priori about things is what we ourselves put into them.*

* The method copied from the investigator of nature is to look for the elements of pure reason within whatever an experiment can confirm or refute. Now, no experiment can be run on the objects of pure reason’s propositions (as can be done in natural science) when those propositions are being tested, particularly when they dare to go past every boundary of possible experience. So an experiment will be workable only with concepts and principles that we adopt a priori. We have to set them up so that one and the same set of objects can be looked at from two sides. On one side they are objects of the senses and understanding for experience. On the other side they are objects that are merely thought—objects, at most, for reason in isolation, striving beyond the boundaries of experience. Suppose we find that, when we look at things from that double point of view, they agree with the principle of pure reason, while from a single point of view reason falls into an unavoidable conflict with itself. Then the experiment settles the matter: the distinction is correct.

This attempt works out as we hoped. The first part of metaphysics deals with a priori concepts, and the matching objects for these can be given in experience, to fit them. For that part, the attempt promises the secure path of a science.

B xix Once we change our way of thinking like this, we can explain the possibility of a priori cognition quite well. What is more, the laws that underlie nature a priori—nature understood as the sum of the objects of experience—can now be given proofs that satisfy. Both were impossible with the old procedure. But our deduction of the power to cognize a priori gives a strange result in the first part of metaphysics. The result seems to do great harm to the whole purpose of metaphysics, which is the business of its second part. It is that, with this power, we can never get beyond the boundary of possible experience. Yet getting beyond that boundary is exactly the most essential concern of this science.

B xx But right here lies an experiment that counter-checks the truth of the result of that first appraisal of our a priori cognition of reason. The result was that this cognition applies only to appearances, and leaves the thing in itself aside, as real on its own account but unknown to us. For something drives us necessarily past the boundary of experience and of every appearance: the unconditioned. Reason demands the unconditioned in things in themselves, necessarily and with every right, for everything conditioned. In that way it demands that the series of conditions be complete. Suppose we find the following. First case: we assume that objects, taken as things in themselves, are what our cognition of experience has to conform to. Then we find we cannot think the unconditioned without contradiction. Second case: we assume that our representation of things, as they are given to us, doesn’t conform to them as things in themselves; instead these objects, as appearances, conform to our manner of representing. Then the contradiction goes away. And we find that, as a consequence, the unconditioned has to turn up, not in things in so far as we know them (the things given to us), but in the same things in so far as we don’t know them, as things in themselves.

B xxi Then it turns out that what we first adopted merely as an experiment is well founded.* Speculative reason is denied any way forward in this field of the supersensible. What remains for us is to try whether practical cognition of reason contains data that can determine that transcendent concept of reason, the unconditioned. In that way, as metaphysics wishes, we would get past the boundary of all possible experience, using our a priori cognition—though one that is possible only for a practical purpose. In doing so, speculative reason has at the very least cleared a space for such an extension, even though the space had to be left empty.

B xxii We are still free to fill it, and reason itself urges us to, with its practical data, if we can.∗∗

* This experiment of pure reason is much like the chemists’ experiment. They sometimes call it the trial of reduction, and in general the synthetic procedure. The metaphysician’s analysis split pure a priori cognition into two very different elements: things as appearances, and things in themselves. Dialectic then combines the two again so that they agree with the necessary idea of reason, the unconditioned. It finds that the agreement can be had only by drawing that distinction, so that the distinction is the true one.

∗∗ Likewise, the central laws governing the motion of the heavenly bodies gave proven certainty to what Copernicus at first assumed only as a hypothesis. They also proved the existence of the invisible force that binds the structure of the world together (Newtonian attraction). That force would have stayed undiscovered forever if Copernicus hadn’t dared, in a way that went against the senses but was still true, to look for the observed motions not in the objects of the sky but in their spectator. In this preface I too put forward only as a hypothesis the change in the way of thinking that is set out in the Critique, which is analogous to that hypothesis. In the treatise itself, though, the proof isn’t hypothetical at all but apodictic, drawn from what space and time, as we represent them, are like, and from the basic concepts of the understanding. I do this just to make the first attempts at such a change noticeable. Such attempts are always hypothetical.

That attempt to change the old procedure of metaphysics is what this critique of pure speculative reason is all about. We carry out a complete revolution in metaphysics, following the example of the geometers and the investigators of nature. The critique is a treatise about method, not a system of the science as such. Even so, it sketches the whole outline of that science, including its boundaries. It also sketches the whole inner structure of its parts.

B xxiii That is because pure speculative reason has a peculiar feature. It can and should measure out its own power according to the different ways it chooses objects for thought. It can and should also list in full the many ways of setting itself problems. And so it can and should draw up the whole preliminary sketch for a system of metaphysics. This is so for the following reasons. On the first point: in a priori cognition, objects can be given only what the thinking subject draws out of itself. On the second point, as regards principles of cognition, pure reason is a wholly separate unit that stands on its own. In it each member is there for all the others, and all are there for each, as in an organized body. No principle can be taken with certainty in one relation unless it has also been examined in its thorough relation to the whole pure use of reason. In return, metaphysics has a rare good fortune, one that no other science of reason dealing with objects can share (for logic is concerned only with the form of thinking as such). Once this critique has put metaphysics on the secure path of a science, it can take in the whole field of cognitions that belong to it. It can then finish its work and lay it down for later generations to use, as capital that can never be increased.

B xxiv That is because the only things it deals with are principles and the restrictions on their use, and these are determined by the principles themselves. As a foundational science, then, it is also obliged to reach this completeness. And it has to be possible to say of metaphysics: nil actum reputans, si quid superesset agendum (“he counts nothing done while anything remains to be done”).

But what kind of treasure is it, someone will ask, that we mean to leave to later generations in a metaphysics that has been purified by critique, and so brought into a lasting state? A quick look at this work will make people think its usefulness is only negative. It teaches us never to venture beyond the boundary of experience with speculative reason. And that is in fact its first use. But the use becomes positive straight away, once we see what follows. Speculative reason ventures beyond its boundary by means of certain principles. Those principles don’t really widen our use of reason. Looked at closely, they inevitably narrow it. They actually threaten to stretch the boundaries of sensibility, where they properly belong, over everything.

B xxv In that way they threaten to push out the pure (practical) use of reason altogether. So a critique that restricts the speculative use of reason is negative, so far as that goes. But it also clears away an obstacle that restricts, or even threatens to wipe out, the practical use. In that way it is in fact of positive and very great value, once we are persuaded that pure reason has a practical use that is absolutely necessary—the moral use. In this use reason inevitably extends itself beyond the boundaries of sensibility. For that it needs no help from speculative reason. But it must be secured against speculative reason’s counteraction, so that it doesn’t fall into contradiction with itself. Denying that this service of the critique is of any positive use is just like saying the police do no good. After all, their chief job is only to bolt the door against the violence that citizens have to fear from one another, so that everybody can go about their affairs calmly and safely. The analytic part of the critique proves the following. Space and time are nothing but forms of sensible intuition, and so nothing but conditions under which things exist as appearances. Next, we have no concepts of the understanding, and so no elements for cognizing things, except under one condition.

B xxvi The condition is that an intuition matching those concepts can be given. So of no object can we have cognition as a thing in itself. We can cognize an object only as appearance, that is, only so far as it is something that sensible intuition can take as its object. From this it follows, of course, that all possible speculative cognition of reason is limited to mere objects of experience. Even so—and this must be well noted—it is always held in reserve that we have to be able at least to think these same objects as things in themselves, though we can’t cognize them that way*. Otherwise we’d get an absurd result.

B xxvii There would be an appearance with nothing there that appears. Suppose we had never drawn the distinction that our critique forces on us. One side of it is things as objects of experience. The other side is those very same things as things in themselves. Then the principle of causality, and with it the mechanism of nature, would have to govern the determination of all things whatever, since all would count as efficient causes. I couldn’t say of one and the same being, for instance the human soul, that its will is free and also that it is subject to natural necessity (which means not free), because I’d be contradicting myself plainly. In both statements I would have taken the soul in exactly the same meaning, as a thing in general (a thing in itself). And without a critique first, I couldn’t have taken it any other way. But the critique teaches us to take the object in two meanings, as appearance or as thing in itself. Suppose it hasn’t erred. Suppose the deduction of its concepts of the understanding is correct, so that the principle of causality holds only for things in the first sense, as objects of experience, while those same things in the second sense are exempt from it.

B xxviii Then the same will, in appearance (in its visible actions), necessarily conforms to the law of nature and so is not free. From the other side, as something that belongs to a thing in itself, that will isn’t subject to the law, and so it is thought of as free. No contradiction arises. Now, looked at from that second side, I can’t cognize my soul by any speculative reason, and still less by empirical observation. Nor can I have cognition of freedom, understood as a property of a being I credit with effects in the world of sense. For that I would have to cognize such a being as determined in its existence, yet not in time. This is impossible, because I can’t put any intuition under my concept. Even so, I can think freedom. That is, thinking of it at least involves no contradiction, as long as our critical distinction stands. That is the distinction between the two kinds of representation (sensible and intellectual), together with the limitation it brings on the pure concepts of the understanding, and so on the principles that flow from them. Suppose now that morality has to presuppose freedom, in its strictest sense, as something belonging to our will, and cites original practical principles in our reason as its a priori data.

B xxix Without freedom as a presupposition, those principles would be flatly impossible. And suppose speculative reason had proved that freedom can’t be thought at all. Then the moral presupposition would have to yield to the other one, the opposite of which contains a plain contradiction. So freedom, and with it morality (whose opposite contains no contradiction unless freedom has already been presupposed), would have to make room for the mechanism of nature. As things stand, though, I need nothing more for morality than this: freedom must only not contradict itself, and so must at least be thinkable, without my needing to see into it any further. It must also not stand in the way of the natural mechanism that governs this same action when it is viewed in a different respect. So the doctrine of morals holds its place, and the doctrine of nature holds its own. That would not have happened if the critique had not first taught us our unavoidable ignorance about things in themselves, and cut back whatever we can know in theory to appearances alone. The same account of the positive use of critical principles of pure reason applies equally to the concept of God and to the simple nature of our soul, though I pass over it to keep this short.

B xxx Unless I take away from speculative reason its pretension to excessive insights at the same time, I couldn’t even accept God, freedom and immortality to serve my reason’s necessary practical use. That is because, to reach those insights, speculative reason has to rely on principles that in truth reach no further than objects of possible experience. When these are applied to something that can’t be an object of experience, they always turn it into an appearance. That is how speculative reason ends up declaring every practical extension of pure reason impossible. So I had to set knowledge aside to make room for faith. The dogmatism of metaphysics—the prejudice that headway in metaphysics can be made with no critique of pure reason—is the real source of all the unbelief that clashes with morality, and that unbelief is, every time, highly dogmatic.—So if it won’t be hard for someone to leave later generations a legacy of systematic metaphysics, written in keeping with the critique of pure reason, that is a gift not to be thought small. It is so whether we look merely at the cultivation of reason through the secure path of a science in general, compared with reason’s baseless groping and careless roaming without a critique.

B xxxi Or we may look at the better use of time by inquisitive young people. Under ordinary dogmatism they get so much encouragement, and so early, to reason comfortably about things they don’t understand, and in which, like everyone in the world, they will never see anything. They are encouraged, too, to go in for inventing new thoughts and opinions, and so to neglect learning solid sciences. It is so most of all when we count the invaluable advantage of ending every objection to morality and religion for all future time, in the Socratic way: by proving beyond doubt that the objectors are ignorant. That matters because some metaphysics or other has been in the world all along, and probably always will be. And with it there will also be a dialectic of pure reason, since that is natural to reason. So the first and most important concern of philosophy is to rid it, once and for all, of every harmful influence by plugging the source of the errors.

* To cognize an object, I have to be able to prove that it is possible. The proof may come from experience, which attests to its actuality, or it may come a priori through reason. But I can think whatever I like, as long as I don’t contradict myself. That is, my concept just has to be a possible thought. I can’t vouch, though, for whether an object corresponding to it exists within the sum of all possibilities. To give such a concept objective validity (real possibility; the first kind was merely logical), something more is required. This something more doesn’t have to be looked for in theoretical sources of cognition. It can lie in practical ones as well.

This change in the field of the sciences is an important one. Speculative reason must lose what it has so far imagined it possessed.

B xxxii Even so, everything stays as it was with the common human concern, and with the benefit the world has so far drawn from the teachings of pure reason. It remains in just as good a state as it ever was. The loss hits only the monopoly of the schools. It doesn’t touch the interest of human beings at all. I ask the most unbending dogmatist: have any of these proofs, once they came out of the schools, ever reached the public and had the slightest influence on its conviction? There is the proof that our soul lasts after death, from the simplicity of substance. There is the proof that the will is free against the general mechanism, built on fine yet feeble distinctions between subjective and objective practical necessity. And there is the proof of God’s existence that starts out from the concept of a being that is the most real of all (or from how contingent anything changeable is, and how necessary a first mover is). That hasn’t happened. And since common human understanding is unfit for such subtle speculation, it can never be expected to happen. Instead, as for the first proof, there is a disposition of human nature that everyone notices: it can never be satisfied by what is temporal, which is inadequate to the dispositions of its whole vocation; that has produced the hope of a future life.

B xxxiii In the case of the second, the plain and clear statement of duties, set against every claim of the inclinations, has produced the consciousness of freedom. And in the third case, nature’s wonderful order, beauty and care, visible everywhere, have by themselves produced faith in a wise and great originator of the world. These alone must produce the conviction that spreads to the public, so far as it rests on grounds of reason. If so, this possession isn’t just left undisturbed. It gains even more standing from the fact that the schools are now taught not to claim any higher or wider insight, on a point that concerns the common human interest, than the insight that the large crowd (the one we have most reason to respect) can reach just as easily. The schools are taught, then, to limit themselves to cultivating only those grounds of proof that everyone can understand and that are enough for moral purposes. So the change affects only the arrogant claims of the schools. In this matter (as rightly in many others) they would like to be taken for the only experts and keepers of such truths. They share with the public only the use of these truths, and hold on to the key (quod mecum nescit, solus vult scire videri).

B xxxiv Even so, provision is also made for a fairer claim of the speculative philosopher. The philosopher remains the exclusive keeper of a science that benefits the public without its being aware of it, namely the critique of reason. For this science can never become popular, and doesn’t need to be. The people have no more taste for finely spun arguments in favor of useful truths than they ever think of equally subtle objections to them. The school, on the other hand, like every person who rises to speculation, inevitably gets caught up in both. So the school is obliged to examine the rights of speculative reason thoroughly, once and for all. That heads off a scandal that must sooner or later reach even the people from the disputes in which metaphysicians (and eventually clergymen too, as metaphysicians) are inevitably entangled without a critique, and which in the end distort their own teachings. Only this critique can cut off at the root materialism, fatalism, atheism, free-thinking unbelief, fanaticism and superstition, all of which can do damage to everyone. In the end it can also cut off idealism and skepticism, which threaten the schools more and are hardly likely to pass into the public.

B xxxv If governments choose to take an interest in the affairs of scholars, it would be much more in keeping with their wise concern for both sciences and people to give such a critique the freedom it needs. Only a critique can put the work of reason on a firm footing. Doing so would suit them far better than backing the schools in their absurd despotism. The schools raise a loud outcry over public danger when someone tears their cobwebs. The public has never taken notice of those cobwebs, and so can never feel their loss.

The critique is not opposed to the dogmatic procedure of reason in its pure cognition, as a science. (That procedure must always be dogmatic, that is, strictly proving from secure a priori principles.) What the critique opposes is dogmatism. Dogmatism is the presumption that one can get on with pure cognition from concepts (philosophical cognition), using principles reason has long been using, without finding out in what way and by what right reason came to them. So dogmatism means reason’s dogmatic procedure in pure cognition, with no critique of its own power beforehand. This opposition isn’t meant to defend talkative shallowness. That shallowness goes under the assumed name of popularity.

B xxxvi Nor is it meant to defend skepticism, which makes short work of all of metaphysics. On the contrary, the critique is the necessary preliminary arrangement for advancing a thorough metaphysics as a science. That science must necessarily be dogmatic, and carried out systematically by the strictest standard, and so in proper scholarly form (not popularly). This demand on metaphysics is not to be waived, since metaphysics undertakes to do its work entirely a priori, and so to the full satisfaction of speculative reason. When the plan that the critique prescribes is put into practice, in the system of metaphysics still to come, we will one day have to follow the strict method of the famous Wolf, the greatest of all dogmatic philosophers. He was the first to show how the secure path of a science is to be taken: by settling principles in a lawful way, defining concepts clearly, trying for strictness of proof, and avoiding bold leaps in drawing conclusions. With this example he also became the founder of Germany’s spirit of thoroughness, which hasn’t gone out yet. For that very reason he was especially able to bring a science like metaphysics into that state, if it had occurred to him to prepare the field first by a critique of the organ, that is, of pure reason itself.

B xxxvii That is a shortcoming to be charged not so much to him as to the dogmatic mindset of his time. Where this is concerned, the philosophers of his day and of every earlier day have no right to blame one another. Those who reject his method of teaching and, at the same time, the critique’s procedure can be after only one thing: shaking off the shackles of science altogether, so that what they get is play in place of work, opinion in place of certainty, and philodoxy in place of philosophy.

As for this second edition, I naturally didn’t want to let its occasion go by without remedying, as far as I could, the difficulties and obscurity. They may have led to some of the misreadings that sharp-minded men have run into when judging this book, perhaps not without fault of mine. I found nothing to change in the propositions as such, or in the arguments that support them, or in the form or completeness of the plan. This is due partly to the long examination I put them through before I laid the work before the public. It is due partly to the nature of the subject itself, namely a pure speculative reason. That reason has a genuine articulated structure, where everything works as an organ. In it everything exists for the sake of one thing.

B xxxviii And each single part exists for the sake of all. So every weakness, however slight, whether a fault (an error) or a lack, must inevitably show itself when the system is used. I hope this system will keep its ground, unchanged. My confidence comes not from conceit but from the evidence of one experiment, getting the same result both ways. One starts from the smallest elements and goes up to the whole of pure reason. The other goes back from the whole to every part (the whole too is given of itself, by reason’s final aim in the practical sphere). This is because any attempt to change even the smallest part brings on contradictions at once, not just in the system but in human reason in general. But the presentation still needs work. In this edition I have tried to improve it, to remedy several things. One is the misunderstanding of the Aesthetic, mainly of the concept of time. Another is the way the deduction of the understanding’s concepts is obscure. A third is the alleged shortage of convincing evidence in the proofs for the principles of the pure understanding. The last is the misreading of the paralogisms that are charged against rational psychology.

B xxxix My changes in the manner of presentation* extend this far and no farther. That is, they go only as far as the point where the first chapter of the transcendental dialectic ends.

B xl The reason is that the time was too short.

B xli And in the rest of the book no expert and impartial examiner had come across any misunderstanding.

B xlii Even though I may not name them and give them the praise they have earned, they will find, in the right places, the notice I took of their remarks. This improvement comes with a small loss for the reader, which couldn’t be prevented unless I let the book grow too bulky. Several things had to be left out or presented in shortened form. They don’t belong essentially to the completeness of the whole. But some readers would be sorry to lose them, because they may serve other purposes. They had to go to make room for my presentation, which I hope is now easier to follow. At bottom it alters not a thing in the propositions, or even in the arguments for them. But here and there it departs so far from the earlier one in its method of presenting that it couldn’t be done by inserting additions. Anyone who likes can make up this small loss by comparing the first edition. And I hope the greater clarity more than makes up for it. In various public writings (partly in reviews of books, partly in separate treatises) I’ve noticed, with grateful pleasure, two things. First, the German spirit of thoroughness is not dead. It was only shouted down, for a short time, by the fashionable tone of a genius-style freedom in thinking.

B xliii Second, the thorny paths of the critique lead to a science of pure reason that is scholarly in form, and as such alone lasting and therefore most necessary. Those paths haven’t kept courageous and bright minds from mastering that science. These deserving men combine so happily the thoroughness of insight with the talent for a clear presentation (which I’m not conscious of having). I leave it to them to finish my treatment where it may still be defective in the latter respect here and there. What an author risks in this situation isn’t refutation. It’s failing to be understood. For my part, I can’t get into disputes from now on. I will, though, pay careful attention to every hint, whether from friends or opponents, so that I can use them in the future working out of the system, in keeping with this preliminary study. In the course of this work I’ve grown fairly far into old age. This month I enter my sixty-fourth year. If I want to carry out my plan to deliver a metaphysics of nature and a metaphysics of morals, as confirmation that the critique of speculative and of practical reason is correct, I have to be sparing with my time. I expect two things from the deserving men who have adopted this work as their own.

B xliv One is the clearing up of the obscurities that were hardly avoidable in this work at first. The other is the defense of the whole. Any philosophical exposition can be picked at in individual passages (it can’t come armored the way a mathematical one does). Meanwhile the articulated structure of the system, viewed as a unity, isn’t in the slightest danger. When a system is new, few people have the nimbleness of mind to take it in at a glance, and fewer still the wish, since every novelty is inconvenient to them. Apparent contradictions can be dug out of any book, especially one written as free discourse, by tearing individual passages out of context and comparing them with each other. In the eyes of someone who relies on other people’s judgment, such contradictions cast an unfavorable light on the book. But someone who has got hold of the idea as a whole will find them easy to dissolve. Still, when a theory stands firm in itself, action and reaction, which at first threatened it with great danger, only serve over time to wear down its rough spots. And if men of impartiality, insight and true popularity take it up, they can also give it the necessary elegance in a short time.

Königsberg, April 1787.

* The only real addition I could name, and even that only in the way of proof, is the one I made through a new refutation of psychological idealism, and a strict proof (the only possible one, I believe) that outer intuition has objective reality, on page 273. Idealism may be taken to be as harmless as you like, so far as the essential aims of metaphysics go (it actually is not harmless). Even so, it remains a scandal to philosophy and to human reason in general that we have to accept the existence of things outside us on faith alone. (From these things we draw the whole material of cognitions, even for our inner sense.) And if someone happens to doubt that existence, we have no satisfying proof to set against them. Because the proof is somewhat obscure in its third through sixth lines, I ask that this sentence be altered to read: “This permanent thing, however, cannot be an intuition in me. For all the grounds that determine my existence and that can be found in me are representations. As representations they themselves require something permanent that is different from them. Only in relation to that permanent thing can their change—and therefore my existence in the time where they change—be determined.” People will probably object to this proof: I am immediately aware only of what is in me, namely my representation of outer things. So it remains undecided whether anything corresponding to it exists outside me or not. Yet I am aware of my existence in time (and thereby of its being determinable in time) through inner experience. That is more than being conscious merely of my representation. But it is the same as the empirical consciousness of my existence, which can be determined only by relation to something that is connected with my existence and is outside me. So my consciousness of existing in time is bound up, as one and the same thing, with consciousness of standing in a relation to something outside me. And what connects the outer inseparably with my inner sense is experience and not invention, sense and not imagination. Outer sense is, after all, in itself a relating of intuition to something real outside me. Its reality, as distinct from imagination, rests only on its being inseparably tied to inner experience itself, as the condition that makes inner experience possible. That is what happens here. Suppose I could join to my intellectual consciousness of existing—the representation I am, which goes along with all my judgments and acts of understanding—a determination of my existence by intellectual intuition. Then awareness of a relation to something outside me wouldn’t have to be part of that determination. As things are, that intellectual consciousness does come first. But my existence can be determined only in inner intuition, and that intuition is sensible and tied to the condition of time. This determination, and with it inner experience itself, depends on something permanent that is not in me. It can therefore depend only on something outside me, something I have to see myself as related to. So the reality of outer sense is tied by necessity to that of inner sense, if experience at all is to be possible. That is, I’m exactly as sure that there are things outside me which stand in relation to my sense as I am sure that I myself exist, determined in time. As for which given intuitions really have objects outside me answering to them, so that they belong to outer sense (to which, and not to imagination, they must be credited), this has to be settled case by case. It is settled using the rules that tell experience in general (inner experience included) from imagination. The proposition that there really is outer experience always underlies this. One more remark can be added. Having a representation of something permanent in existence is not the same as having a permanent representation. A permanent representation can be very changeable and shifting, like all our representations, even the representations of matter. Yet it relates to something permanent. That must therefore be an outer thing, distinct from all my representations. The existence of that thing is necessarily bound up with determining my own existence, and the two together make up a single experience. That experience wouldn’t even take place inwardly if it were not (in part) outward at the same time. The How? can’t be explained any further here, any more than we can explain how we think the abiding in time at all. Its existing together with what changes produces the concept of change.