Critique of Pure Reason

by Immanuel Kant

  Under the sway of reason our knowledge must not remain a rhapsody, but must become a system, because thus alone can the essential objects of reason be supported and advanced. By system I mean the unity of various kinds of knowledge under one idea. This is the concept given by reason of the form of the whole, in which concept both the extent of its manifold contents and the place belonging to each part are determined a priori. This scientific concept of reason contains, therefore, the end and also the form of the whole which is congruent with it. The unity of the end to which all parts relate and through the idea of which they are related to each other, enables us to miss any part, if we possess a knowledge of the rest, and prevents any arbitrary addition or vagueness of perfection of which the limits could not be determined a priori. Thus the whole is articulated (articulatio), not aggregated (coacervatio). It may grow internally (per intussusceptionem), but not externally (per appositionem), like an animal body, the growth of which does not add any new member, but, without changing their proportion, renders each stronger and more efficient for its purposes.

  The idea requires for its realisation a schema, that is an essential variety, and an order of its parts, which are determined a priori, according to the principles inherent in its aim. A schema, which is not designed according to an idea, that is, according to the principal aim of reason, but empirically only, in accordance with accidental aims (the number of which cannot be determined beforehand) gives technical unity; but the schema which originates from an idea only (where reason dictates the aims a priori and does not wait for them in experience) supplies architectonical unity. Now what we call a science, the schema of which must have its outline (monogramma) and the division of the whole into parts devised according to the idea, that is, a priori, and keep it perfectly distinct from everything else according to principles, cannot be produced technically according to the similarity of its various parts or the accidental use of knowledge in concreto for this or that external purpose, but architectonically only, as based on the affinity of its parts and their dependence on one supreme and internal aim through which alone the whole becomes possible.

  No one attempts to construct a science unless he can base it on some idea; but in the elaboration of it the schema, nay, even the definition, which he gives in the beginning of his science, corresponds very seldom to his idea which, like a germ, lies hidden in reason, and all the parts of which are still enveloped and hardly distinguishable even under microscopical observation. It is necessary, therefore, to explain and determine all sciences, considering that they are contrived from the point of view of a certain general interest, not according to the description given by their author, but according to the idea which, from the natural unity of its constituent parts, we may discover as founded in reason itself. We shall often find that the originator of a science, and even his latest successors are moving vaguely round an idea which they have not been able to perceive clearly, failing in consequence to determine rightly the proper contents, the articulation (systematical unity), and the limits of their science.

  It is a misfortune that only after having collected for a long time at haphazard, under the influence of an idea that lies hidden in us, materials belonging to a science, nay, after having for a long time fitted them together technically, a time arrives when we are able to see its idea in a clearer light, and to devise architectonically a whole system according to the aims of reason. Systems seem to develop like worms through a kind of generatio aequivoca, by the mere aggregration of numerous concepts, at first imperfect, and gradually attaining to perfection, though in reality they all had their schema, as their original germ, in reason which was itself being developed. Hence, not only is each of them articulated according to an idea, but all may be properly combined with each other in a system of human knowledge, as members of one whole, admitting of an architectonic of all human knowledge which in our time, when so much material has been collected or may be taken over from the ruins of old systems, is not only possible, but not even very difficult. We shall confine ourselves here to the completion of our proper business, namely, to sketch the architectonic of all knowledge arising from pure reason, beginning only at the point where the common root of our knowledge divides into two stems, one of which is reason. By reason, however, I understand here the whole higher faculty of knowledge, and I distinguish therein rational from empirical knowledge.

  If I take no account of the contents of knowledge, objectively considered, all knowledge is, from a subjective point of view, either historical or rational. Historical knowledge is cognitio ex datis, rational knowledge cognitio ex principiis. Whatever may be the first origin of some branch of knowledge, it is always historical, if he who possesses it knows only so much of it as has been given to him from outside, whether through immediate experience, or through narration, or by instruction also (in general knowledge). Hence a person who, in the usual sense, has learnt a system of philosophy, for instance the Wolfian, though he may carry in his head all the principles, definitions, and proofs, as well as the division of the whole system, and have it all at his fingers' ends, possesses yet none but a complete historical knowledge of the Wolfian philosophy. His knowledge and judgments are no more than what has been given him. If you dispute any definition, he does not know whence to take another, because he formed his own on the reason of another. But the imitative is not the productive faculty, that is, knowledge in his case did not come from reason, and though objectively it is rational knowledge, subjectively it is historical only. He has taken and kept, that is, he has well learned and has become a plaster cast of a living man. Knowledge, which is rational objectively (that is, which can arise originally from a man's own reason only), can then only be so called subjectively also; when they have been drawn from the general resources of reason, that is, from principles from which also criticism, nay, even the rejection of what has been learnt, may arise.

  All knowledge of reason is again either based on concepts or on the construction of concepts; the former being called philosophical, the latter mathematical. Of their essential difference I have treated in the first chapter. Knowledge, as we saw, may be objectively philosophical, and yet subjectively historical, as is the case with most apprentices, and with all who never look beyond their school and remain in a state of pupilage all their life. But it is strange that mathematical knowledge, as soon as it has been acquired, may be considered, subjectively also, as knowledge of reason, there being no such distinction here as in the case of philosophical knowledge. The reason is that the sources from which alone the mathematical teacher can take his knowledge lie nowhere but in the essential and genuine principles of reason, and cannot be taken by the pupil from anywhere else, nor ever be disputed, for the simple ground that the employment of reason takes place here in concreto only, although a priori, namely, in the pure and therefore faultless intuition, thus excluding all illusion and error. Of all the sciences of reason (a priori), therefore, mathematics alone can be learnt, but philosophy (unless it be historically) never; with regard to reason we can at most learn to philosophise.

  The system of all philosophical knowledge is called philosophy. It must be taken objectively, if we understand by it the type of criticising all philosophical attempts, which is to serve for the criticism of every subjective philosophy, however various and changeable the systems may be. In this manner philosophy is a mere idea of a possible science which exists nowhere in concreto, but which we may try to approach on different paths, until in the end the only true path, though overgrown and hidden by sensibility, has been discovered, and the image, which has so often proved a failure, has become as like the original type as human power can ever make it. Till then we cannot learn philosophy; for where is it, who possesses it, and how shall we know it? We can only learn to philosophise, that is, to exercise the talent of reason, according to its general principles, on certain given attempts always, however, with the reservation of the right of reason of investigating the sources of these principles themselves, and of
either accepting or rejecting them.

  So far the concept of philosophy is only scholastic, as of a system of knowledge which is sought and valued as a science, without aiming at more than a systematical unity of that knowledge, and therefore the logical perfection of it. But there is also a universal, or, if we may say so, a cosmical concept (conceptus cosmicus) of philosophy, which always formed the real foundation of that name, particularly when it had, as it were, to be personified and represented in the ideal of the philosopher, as the original type. In this sense philosophy is the science of the relation of all knowledge to the essential aims of human reason (teleologia rationis humanae), and the philosopher stands before us, not as an artist, but as the lawgiver of human reason. In that sense it would be very boastful to call oneself a philosopher, and to pretend to have equalled the type which exists in the idea only.

  The mathematician, the student of nature, and the logician, however far the two former may have advanced in rational, and the last, particularly, in philosophical knowledge, are merely artists of reason. There is besides, an ideal teacher, who controls them all, and uses them as instruments for the advancement of the essential aims of human reason. Him alone we ought to call philosopher: but as he exists nowhere, while the idea of his legislation exists everywhere in the reason of every human being, we shall keep entirely to that idea, and determine more accurately what kind of systematical unity philosophy, in this cosmical concept,1 demands from the standpoint of its aims.

  Essential ends are not as yet the highest ends; in fact, there can be but one highest end, if the perfect systematical unity of reason has been reached. We must distinguish, therefore, between the ultimate end and subordinate ends, which necessarily belong, as means, to the former. The former is nothing but the whole destination of man, and the philosophy which relates to it is called moral philosophy. On account of this excellence which distinguishes moral philosophy from all other operations of reason, the ancients always understood under the name of philosopher the moralist principally: and even at present the external appearance of self-control by means of reason leads us, through a certain analogy, to call a man a philosopher, however limited his knowledge may be. The legislation of human reason (philosophy) has two objects only, nature and freedom, and contains therefore both the law of nature and the law of morals, at first in two separate systems, but combined, at last, in one great system of philosophy. The philosophy of nature relates to all that is; that of morals to that only that ought to be.

  All philosophy is either knowledge derived from pure reason, or knowledge of reason derived from empirical principles. The former is called pure, the latter empirical philosophy.

  The philosophy of pure reason is either propaedeutic (preparation), enquiring into the faculties of reason, with regard to all pure knowledge a priori, and called critic, or, secondly, the system of pure reason (science), comprehending in systematical connection the whole (both true and illusory) of philosophical knowledge, derived from pure reason, and called metaphysic,—although this name of metaphysic may be given also to the whole of pure philosophy, inclusive of the critic, in order thus to comprehend both the investigation of all that can ever be known a priori and the representation of all that constitutes a system of pure philosophical knowledge of that kind, excluding all that belongs to the empirical and the mathematical employment of reason.

  Metaphysic is divided into that of the speculative and that of the practical use of pure reason, and is, therefore, either metaphysic of nature or metaphysic of morals. The former contains all the pure principles of reason, derived from concepts only (excluding therefore mathematics), of the theoretical knowledge of all things, the latter, the principles which determine a priori and necessitate all doing and not doing. Morality is the only legality of actions that can be derived from principles entirely a priori. Hence the metaphysic of morals is really pure moral philosophy, in which no account is taken of anthropology or any empirical conditions. Metaphysic of speculative reason has commonly been called metaphysic, in the more limited sense; as however pure moral philosophy belongs likewise to this branch of human and philosophical knowledge, derived from pure reason, we shall allow it to retain that name, although we leave it aside for the present as not belonging to our immediate object.

  It is of the highest importance to isolate various sorts of knowledge, which in kind and origin are different from others, and to take great care lest they be mixed up with those others with which, for practical purposes, they are generally united. What is done by the chemist in the analysis of substances, and by the mathematician in pure mathematics, is far more incumbent on the philosopher, in order to enable him to define clearly the part which, in the promiscuous employment of the understanding, belongs to a special kind of knowledge, as well as its peculiar value and influence. Human reason, therefore, since it first began to think, or rather to reflect, has never been able to do without a metaphysic, but it has never kept it sufficiently free from all foreign admixture. The idea of a science of this kind is as old as speculation itself, and what human reason does not speculate, whether in a scholastic or a popular manner? It must be admitted, however, that even thinkers by profession did not clearly distinguish between the two elements of our knowledge, the one being in our possession completely a priori, the other deducible a posteriori only from experience, and did not succeed therefore in fixing the limits of a special kind of knowledge, nor in realising the true idea of a science which had so long and so deeply engaged the interest of human reason. When it was said that metaphysic is the science of the first principles of human knowledge, this did not mark out any special kind of knowledge, but only a certain rank or degree, with regard to its character of generality, which was not sufficient to distinguish it clearly from empirical knowledge. For among empirical principles also, some are more general, and therefore higher than others; and in such a series of subordinated principles (where that which is entirely a priori is not distinguished from that which is known a posteriori only), where should one draw the line to separate the first part from the last, and the higher members from the lower? What should we say if chronology should distinguish the epochs of history no better than by dividing it into the first centuries and the subsequent centuries? We should ask, no doubt, whether the fifth or the tenth belongs to the first centuries? and I ask in the same way whether the concept of what is extended belongs to metaphysic? If you say, yes! I ask, what about the concept of a body? and of a liquid body? You then hesitate, for you begin to see, that if I continue in this strain, everything would belong to metaphysic. It thus becomes clear that the mere degree of subordination of the special under the general cannot determine the limits of a science; but, in our case, only the complete difference in kind and origin. The fundamental idea of metaphysic was obscured on another side because, as knowledge a priori, it showed a certain similarity in kind with mathematics. The two are, no doubt, related with regard to their origin a priori, but, if we consider how, in metaphysic, knowledge is derived from concepts, while in mathematics we can only form judgments through the construction of concepts a priori, we discover, in comparing philosophical with mathematical knowledge, the most decided difference in kind, which was no doubt always felt, but never determined by clear criteria. Thus it has happened that, as philosophers themselves blundered in developing the idea of their science, its elaboration could have no definite aim, and no certain guidance; and we may well understand how metaphysical science was brought into contempt in the outside world, and at last among philosophers themselves, considering how arbitrarily it had been designed, and how constantly those very philosophers, ignorant as to the path which they ought to take, were disputing among themselves about the discoveries which each asserted he had made on his own peculiar path.

  All pure knowledge a priori constitutes, therefore, according to the special faculty of knowledge in which alone it can originate, a definite unity; and metaphysic is that philosophy which is meant to represent that knowledge in its sy
stematical unity. Its speculative part, which has especially appropriated that name, namely, what we call metaphysic of nature, in which everything is considered from concepts a priori, so far as it is (not so far as it ought to be), will have to be divided in the following manner.

  Metaphysic, in the more limited sense of the word, consists of transcendental philosophy and the physiology of pure reason. The former treats only of understanding and reason themselves, in a system of all concepts and principles which have reference to objects in general, without taking account of objects that may be given (ontologia): the latter treats of nature, that is, the sum of given objects (whether given to the senses, or, if you like, to some other kind of intuition) and is therefore physiology, although rationalis only. The employment of reason in this rational study of nature is either physical or hyperphysical, or, more accurately speaking, immanent or transcendent. The former refers to nature, in so far as its knowledge can take place in experience (in concreto); the latter to that connection of objects of experience which transcends all experience. This transcendent physiology has for its object either an internal or an external connection, both transcending every possible experience; the former is the physiology of nature as a whole, or transcendental knowledge of the world, the latter refers to the connection of the whole of nature with a Being above nature, and is therefore transcendental knowledge of God.

  Immanent physiology, on the contrary, considers nature as the sum total of all objects of the senses, such, therefore, as it is given us, but only according to conditions a priori, under which alone it can be given us. It has two kinds of objects only; first, those of the external senses, which constitute together corporeal nature; secondly, the object of the internal sense, the soul, and what, according to its fundamental principles in general, may be called thinking nature. The metaphysic of corporeal nature is called physic, or, because it must contain the principles of an a priori knowledge of nature only, rational physic. Metaphysic of the thinking nature is called psychology, and for the same reason, is here to be understood as the rational knowledge only of that nature. Thus the whole system of metaphysic consists of four principal parts. 1. Ontology, 2. Rational Physiology, 3. Rational Cosmology, 4. Rational Theology. The second part, the physiology of pure reason, contains two divisions, namely, physica rationalis,2 and phychologia rationalis.