Our knowledge springs from two fundamental sources of our mind; the first is to receive representations (receptivity of impressions), the second is the faculty of knowing an object through these representations (spontaneity of concepts). Through the first an object is *given* to us, through the second the object is *thought* in relation to that representation (which is a mere determination of the mind). Intuition and concepts constitute, therefore, the elements of all our knowledge, so that neither concepts without an intuition in some way corresponding to them, nor intuition without concepts can yield knowledge. Both are either pure or empirical. They are empirical when they contain sensation (sensation presupposes the actual presence of the object). They are *pure* when no sensation is mixed in with the representation. Sensation may be called the matter of sensible knowledge. Pure intuition, therefore, contains only the form under which something is intuited, and the pure concepts contains only the form of thinking an object in general. Pure intuitions and pure concepts alone are possible *a priori*, empirical intuitions and empirical concepts only *a posteriori*. We call *sensibility* the *receptivity* of our mind to receive representations insofar as it is in some wise affected, while the *understanding*, on the other hand, is our faculty of producing representations by ourselves, or the *spontaneity* of knowledge. We are so constituted that our intuition can never be other than *sensible*; that is, it contains only the mode in which we are affected by objects. The faculty, on the contrary, which enables us to *think* the object of sensible intuition is the *understanding*. Neither of these properties is to be preferred to the other. Without sensibility no object would be given to us, without understanding no object would be thought. Thoughts without content are empty, intuitions without concepts are blind. It is, therefore, just as necessary to make our concepts sensible (i.e., to add the object to them in intuition) as to make our intuitions understandable (i.e., to bring them under concepts). These two faculties or capacities cannot exchange their functions. The understanding cannot intuit anything, the senses cannot think anything. Only from their union can knowledge arise. But this is no reason for confounding their respective contributions; rather, it gives us a strong reason for carefully separating and distinguishing the one from the other. We therefore distinguish the science of the rules of sensibility in general, i.e., aesthetic, from the science of the rules of the understanding in general, i.e., logic."―Transcendental Doctrine of Elements. Transcendental Logic: The Idea of a Transcendental Logic
It will be seen how there can be the idea of a special science, the *critique of pure reason* as it may be called. For reason is the faculty which supplies the *principles* of *a priori* knowledge. Pure reason therefore is that which contains the principles of knowing something entirely *a priori*. An *organon* of pure reason would be the sum total of the principles by which all pure *a priori* knowledge can be acquired and actually established. Exhaustive application of such an organon would give us a system of pure reason. But as this would be a difficult task, and as at present it is still doubtful whether indeed an expansion of our knowledge is possible here at all, we may regard a science that merely judges pure reason, its sources and limits, as the *propaedeutic* to the system of pure reason. In general, it would have to be called only a *critique*, not a *doctrine* of pure reason. Its utility, in regard to speculation, would only be negative, for it would serve only to purge rather than to expand our reason, and, which after all is a considerable gain, would guard reason against errors. I call all knowledge *transcendental* which deals not so much with objects as with our manner of knowing objects insofar as this manner is to be possible *a priori*. A system of such concepts would be called *transcendental philosophy*. But this is still, as a beginning, too great an undertaking. For since such a science must contain completely both analytic and synthetic *a priori* knowledge, it is, as far as our present purpose is concerned, much too comprehensive. We will be satisfied to carry the analysis only so far as is indispensably necessary in order to understand in their whole range the principles of *a priori* synthesis, with which alone we are concerned. This investigation, which properly speaking should be called only a transcendental critique but not a doctrine, is all we are dealing with at present. It is not meant to expand our knowledge but only to correct it, and to become the touchstone of the value, or lack of value, of all *a priori* knowledge. Such a critique is therefore the preparation, as far as possible, for a new organon, or, if this should turn out not to be possible, for a canon at least, according to which, thereafter, the complete system of a philosophy of pure reason, whether it serve as an expansion or merely as a limitation of its knowledge, may be carried out both analytically and synthetically. That such a system is possible, indeed that it need not be so comprehensive as to cut us off from the hope of completing it, may already be gathered from the fact that it would have to deal not with the nature of things, which is inexhaustible, but with the understanding which makes judgments about the nature of things, and with this understanding again only as far as its *a priori* knowledge is concerned. The supply of this *a priori* knowledge cannot be hidden from us, as we need not look for it outside the understanding, and we may suppose this supply to prove sufficiently small for us to record completely, judge as to its value or lack of value and appraise correctly. Still less ought we to expect here a critique of books and systems of pure reason, but only the critique of the faculty of pure reason itself. Only once we are in possession of this critique do we have a reliable touchstone for estimating the philosophical value of old and new works on this subject. Otherwise, an unqualified historian and judge does nothing but pass judgments upon the groundless assertions of others by means of his own, which are equally groundless.
Metaphysics, a completely isolated and speculative branch of rational knowledge which is raised above all teachings of experience and rests on concepts only (not, like mathematics, on their application to intuition), in which reason therefore is meant to be its own pupil, has hitherto not had the good fortune to enter upon the secure path of a science, although it is older than all other sciences, and would survive even if all the rest were swallowed up in the abyss of an all-destroying barbarism. Reason in metaphysics, even if it tries, as it professes, only to gain *a priori* insight into those laws which are confirmed by our most common experience, is constantly being brought to a standstill, and we are obliged again and again to retrace our steps, as they do not lead us where we want to go. As to unanimity among its participants, there is so little of it in metaphysics that it has rather become an arena that would seem especially suited for those who wish to exercise themselves in mock fights, where no combatant has as yet succeeded in gaining even an inch of ground that he could call his permanent possession. There cannot be any doubt, therefore, that the method of metaphysics has hitherto consisted in a mere random groping, and, what is worst of all, in groping among mere concepts.What, then, is the reason that this secure scientific course has not yet been found? Is this, perhaps, impossible? Why, in that case, should nature have afflicted our reason with the restless aspiration to look for it, and have made it one of its most important concerns? What is more, how little should we be justified in trusting our reason, with regard to one of the most important objects of which we desire knowledge, it not only abandons us, but lures us on by delusions, and in the end betrays us! Or, if hitherto we have only failed to meet with the right path, what indications are there to make us hope that, should we renew our search, we shall be more successful than others before us?"―from_Critique of Pure Reason_. Preface to the Second Edition. Translated, edited, and with an Introduction by Marcus Weigelt, based on the translation by Max Müller, p. 17
A similar experiment may be tried in metaphysics as regards the *intuition* of objects. If the intuition had to conform to the constitution of objects, I would not understand how we could know anything of them *a priori*; but if the object (as object of the senses) conformed to the constitution of our faculty of intuition, I could very well conceive such a possibility. As, however, I cannot rest in these intuitions if they are to become knowledge, but have to refer them as representations, to something as their object, and must determine this object through them, I can assume either that the *concepts* through which I arrive at this determination also conform to the object, and I would again be as perplexed about how I can know anything about it *a priori*; or else that the objects, or what is the same thing, the *experience* in which alone they are known (as objects that are given to us), conform to those concepts. In the latter case, I recognize an easier solution because experience itself is a kind of knowledge that requires understanding; and this understanding has its rules which I must presuppose as existing within me even before objects are given to me, and hence *a priori*. These rules are expressed in *a priori* concepts to which all objects of experience must necessarily conform, and with which they must agree. With regard to objects, insofar as they are thought merely through reason and thought indeed as necessary, and which can never, at least not in the way in which reason thinks them, be given in experience, the attempts at thinking them (for they must admit of being thought) will subsequently furnish an excellent touchstone of what we are adopting as our new method of thought, namely, that we know of things *a priori* only that which we ourselves put into them."―from_Critique of Pure Reason_. Preface to the Second Edition. Translated, edited, and with an Introduction by Marcus Weigelt, based on the translation by Max Müller, pp. 18-19
This experiment succeeds as hoped and promises to metaphysics, in its first part, which deals with those *a priori* concepts to which the corresponding objects may be given in experience, the secure course of a science. For by thus changing our point of view, the possibility of *a priori* knowledge can well be explained, and, what is still more, the laws which *a priori* lie at the foundation of nature, as the sum total of the objects of experience, may be supplied with satisfactory proofs, neither of which was possible within the procedure hitherto adopted. But there arises from this deduction of our faculty of knowing *a priori*, as given in the first part of metaphysics, a somewhat startling result, apparently most detrimental to that purpose of metaphysics which has to be treated in its second part, namely the impossibly of using this faculty to transcend the limits of possible experience, which is precisely the most essential concern of the science of metaphysics. But here we have exactly the experiment which, by disproving the opposite, establishes the truth of the first estimate of our *a priori* rational knowledge, namely, that it is directed only at appearances and must leave the thing in itself as real for itself but unknown to us. For that which necessarily impels us to to go beyond the limits of experience and of all appearances is the *unconditioned*, which reason rightfully and necessarily demands, aside from everything conditioned, in all things in themselves, so that the series of conditions be completed. If, then, we find that, under the supposition that our empirical knowledge conforms to objects as things in themselves, the unconditioned *cannot be thought without contradiction*, while under the supposition that our representation of things as they are given to us does not conform to them as things in themselves, but, on the contrary, that these objects as appearance conform to our mode of representation, then *the contradiction vanishes*; and if we find, therefore, that the unconditioned cannot be encountered in things insofar as we are acquainted with them (insofar as they are given to us), but only in things insofar as we are not acquainted with them, that is, insofar as they are things in themselves; then it becomes apparent that what we at first assumed only for the sake of experiment is well founded. However, with speculative reason unable to make progress in the field of the supersensible, it is still open to us to investigate whether in reason's practical knowledge data may not be found which would enable us to determine that transcendent rational concept of the unconditioned, so as to allow us, in accordance with the wish of metaphysics, to get beyond the limits of all possible experience with our *a priori* knowledge, which is possible in practical matters only. Within such a procedure, speculative reason has always at least created a space for such an expansion, even if it has to leave it empty; none the less we are at liberty, indeed we are summoned, to fill it, if we are able to do so, with practical *data* of reason."―from_Critique of Pure Reason_. Preface to the Second Edition. Translated, edited, and with an Introduction by Marcus Weigelt, based on the translation by Max Müller, pp. 19-21
The purpose of this critique of pure speculative reason consists in the attempt to change the old procedure of metaphysics, and to bring about a complete revolution after the example set by geometers and investigators of nature. This critique is a treatise on the method, not a system of the science itself; but nevertheless it marks out the whole plan of this science, both with regard to its limits and with regard to its inner organization. For it is peculiar to pure speculative reason that it is able, indeed bound, to measure its own powers according to the different ways in which it chooses its objects for thought, and to enumerate exhaustively the different ways of choosing its problems, thus tracing a complete outline of a system of metaphysics. This is due to the fact that, with regard to the first point, nothing can be attributed to objects in *a priori* knowledge, except what the thinking subject takes from within itself; while, with regard to the second point, pure reason, as far as its principles of knowledge are concerned, forms a separate and independent unity, in which, as in an organized body, every member exists for the sake of all the others, and all the others exist for the sake of the one, so that no principle can be safely applied in *one* relation unless it has been carefully examined in *all* its relations to the whole use of pure reason. Hence, too, metaphysics has this singular advantage, an advantage which cannot be shared by any other rational science which has to deal with objects (for *logic* deals only with the form of thought in general), that if by means of this critique it has been set upon the secure course of a science, it can exhaustively grasp the entire field of knowledge pertaining to it, and can thus finish its work and leave it to posterity as a capital that can never be added to, because it has to deal only with principles and with the limitations of their use, as determined by these principles themselves. And this completeness becomes indeed an obligation if metaphysics is to be a fundamental science, of which we must be able to say, *nil actum reputants, si quid superesset agendum* [to think that nothing was done for as long as something remained to be done]." ―from_Critique of Pure Reason_. Preface to the Second Edition. Translated, edited, and with an Introduction by Marcus Weigelt, based on the translation by Max Müller, pp. 21-22
On the other hand, the moral law, although it gives no such prospect, does provide a fact absolutely inexplicable from any data of the world of sense or from the whole compass of the theoretical use of reason, and this fact points to a pure intelligible world―indeed, it defines it positively and enable us to know something of it, namely a law.This law gives to the sensible world, as sensuous nature (as this concerns rational beings), the form of an intelligible world, i.e., the form of supersensuous nature, without interfering with the mechanism of the former. Nature, in the widest sense of the word, is the existence of things under laws. The sensuous nature of rational beings in general is their existence under empirically conditioned laws, and therefore it is, from the point of view of reason, heteronomy. The supersensuous nature of the same beings, on the other hand, is their existence according to laws which are independent of all empirical conditions and which therefore belong to the autonomy of pure reason. And since the laws, according to which the existence of things depends on cognition, are practical, supersensuous nature, so far as we can form a concept of it, is nothing else than nature under the autonomy of the pure practical reason. The law of this autonomy is the moral law, and it, therefore, is the fundamental law of supersensuous nature and of a pure world of the understanding, whose counterpart must exist in the world of sense without interfering with the laws of the latter. The former could be called the archetypal world (*natura archetypa*) which we know only by reason; the latter, on the other hand, could be called the ectypal world (*natura ectypa*), because it contains the possible effect of the idea of the former as the determining ground of the will."―from_Critique of Practical Reason_. Translated, with an Introduction by Lewis White Beck, p. 44.
Our critique is not opposed to the *dogmatic procedure* of reason in its pure knowledge as science (for science must always be dogmatic, that is, derive its proof from secure *a priori* principles), but only to *dogmatism*, that is, to the presumption that it is possible to make any progress with pure (philosophical) knowledge from concepts according to principles, such as reason has long been in the habit of using, without first inquiring in what way, and by what right, it has come to posses them. Dogmatism is therefore the dogmatic procedure of pure reason, *without a preceding critique of its own powers*; and our opposition to this is not intended to defend that loquacious shallowness which arrogates to itself the name of popularity, much less that skepticism which makes short work of the whole of metaphysics. On the contrary, our critique is meant to form a necessary preparation in support of metaphysics as a thorough science, which must necessarily be carried out dogmatically and strictly systematically, so as to satisfy all the demands, no so much of the public at large, as of the Schools. This is an indispensable demand for it has undertaken to carry out its work entirely *a priori*, and thus to carry it out to the complete satisfaction of speculative reason. In the execution of this plan, as traced out by the critique, that is, in a future system of metaphysics, we shall have to follow the strict method of the celebrated Wolff, the greatest of all dogmatic philosophers. He was the first to give an example (and by his example initiated, in Germany, that spirit of thoroughness which is not yet extinct) of how the secure course of a science could be attained only through the lawful establishment of principles, the clear determination of concepts, the attempt at strictness of proof and avoidance of taking bold leaps in our inferences. He was therefore most eminently qualified to give metaphysics the dignity of a science, if it had only occurred to him to prepare his field in advance by criticism of the organ, that is, of pure reason itself―an omission due not so much to himself as to the dogmatic mentality of his age, about which the philosophers of his own, as well as of all previous times, have no right to reproach one another. Those who reject both the method of Wolff and the procedure of the critique of pure reason can have no other aim but to shake off the fetters of *science* altogether, and thus to change work into play, certainty into opinion and philosophy into philodoxy." ―from_Critique of Pure Reason_. Preface to the Second Edition. Translated, edited, and with an Introduction by Marcus Weigelt, based on the translation by Max Müller, pp. 28-29