The Critique of Pure Reason

Transcendental Doctrine of Method (continued)

Metaphysic is divided into that of the speculative and that of the practical use of pure reason, and is, accordingly, either the metaphysic of nature, or the metaphysic of ethics. The former contains all the pure rational principles—based upon conceptions alone (and thus excluding mathematics)—of all theoretical cognition; the latter, the principles which determine and necessitate à priori all action. Now moral philosophy alone contains a code of laws—for the regulation of our actions—which are deduced from principles entirely à priori. Hence the metaphysic of ethics is the only pure moral philosophy, as it is not based upon anthropological or other empirical considerations. The metaphysic of speculative reason is what is commonly called metaphysic in the more limited sense. But as pure moral philosophy properly forms a part of this system of cognition, we must allow it to retain the name of metaphysic, although it is not requisite that we should insist on so terming it in our present discussion.

It is of the highest importance to separate those cognitions which differ from others both in kind and in origin, and to take great care that they are not confounded with those with which they are generally found connected. What the chemist does in the analysis of substances, what the mathematician in pure mathematics, is, in a still higher degree, the duty of the philosopher, that the value of each different kind of cognition, and the part it takes in the operations of the mind, may be clearly defined. Human reason has never wanted a metaphysic of some kind, since it attained the power of thought, or rather of reflection; but it has never been able to keep this sphere of thought and cognition pure from all admixture of foreign elements. The idea of a science of this kind is as old as speculation itself; and what mind does not speculate—either in the scholastic or in the popular fashion? At the same time, it must be admitted that even thinkers by profession have been unable clearly to explain the distinction between the two elements of our cognition—the one completely à priori, the other à posteriori; and hence the proper definition of a peculiar kind of cognition, and with it the just idea of a science which has so long and so deeply engaged the attention of the human mind, has never been established. When it was said: “Metaphysic is the science of the first principles of human cognition,” this definition did not signalize a peculiarity in kind, but only a difference in degree; these first principles were thus declared to be more general than others, but no criterion of distinction from empirical principles was given. Of these some are more general, and therefore higher, than others; and—as we cannot distinguish what is completely à priori from that which is known to be à posteriori—where shall we draw the line which is to separate the higher and so-called first principles, from the lower and subordinate principles of cognition? What would be said if we were asked to be satisfied with a division of the epochs of the world into the earlier centuries and those following them? “Does the fifth, or the tenth century belong to the earlier centuries?” it would be asked. In the same way I ask: Does the conception of extension belong to metaphysics? You answer, “Yes.” Well, that of body too? “Yes.” And that of a fluid body? You stop, you are unprepared to admit this; for if you do, everything will belong to metaphysics. From this it is evident that the mere degree of subordination—of the particular to the general—cannot determine the limits of a science; and that, in the present case, we must expect to find a difference in the conceptions of metaphysics both in kind and in origin. The fundamental idea of metaphysics was obscured on another side by the fact that this kind of à priori cognition showed a certain similarity in character with the science of mathematics. Both have the property in common of possessing an à priori origin; but, in the one, our knowledge is based upon conceptions, in the other, on the construction of conceptions. Thus a decided dissimilarity between philosophical and mathematical cognition comes out—a dissimilarity which was always felt, but which could not be made distinct for want of an insight into the criteria of the difference. And thus it happened that, as philosophers themselves failed in the proper development of the idea of their science, the elaboration of the science could not proceed with a definite aim, or under trustworthy guidance. Thus, too, philosophers, ignorant of the path they ought to pursue and always disputing with each other regarding the discoveries which each asserted he had made, brought their science into disrepute with the rest of the world, and finally, even among themselves.

All pure à priori cognition forms, therefore, in view of the peculiar faculty which originates it, a peculiar and distinct unity; and metaphysic is the term applied to the philosophy which attempts to represent that cognition in this systematic unity. The speculative part of metaphysic, which has especially appropriated this appellation—that which we have called the metaphysic of nature—and which considers everything, as it is (not as it ought to be), by means of à priori conceptions, is divided in the following manner.

Metaphysic, in the more limited acceptation of the term, consists of two parts—transcendental philosophy and the physiology of pure reason. The former presents the system of all the conceptions and principles belonging to the understanding and the reason, and which relate to objects in general, but not to any particular given objects (Ontologia); the latter has nature for its subject-matter, that is, the sum of given objects—whether given to the senses, or, if we will, to some other kind of intuition—and is accordingly physiology, although only rationalis. But the use of the faculty of reason in this rational mode of regarding nature is either physical or hyperphysical, or, more properly speaking, immanent or transcendent. The former relates to nature, in so far as our knowledge regarding it may be applied in experience (in concreto); the latter to that connection of the objects of experience, which transcends all experience. Transcendent physiology has, again, an internal and an external connection with its object, both, however, transcending possible experience; the former is the physiology of nature as a whole, or transcendental cognition of the world, the latter of the connection of the whole of nature with a being above nature, or transcendental cognition of God.

Immanent physiology, on the contrary, considers nature as the sum of all sensuous objects, consequently, as it is presented to us—but still according to à priori conditions, for it is under these alone that nature can be presented to our minds at all. The objects of immanent physiology are of two kinds: 1. Those of the external senses, or corporeal nature; 2. The object of the internal sense, the soul, or, in accordance with our fundamental conceptions of it, thinking nature. The metaphysics of corporeal nature is called physics; but, as it must contain only the principles of an à priori cognition of nature, we must term it rational physics. The metaphysics of thinking nature is called psychology, and for the same reason is to be regarded as merely the rational cognition of the soul.

Thus the whole system of metaphysics consists of four principal parts: 1. Ontology; 2. Rational Physiology; 3. Rational cosmology; and 4. Rational theology. The second part—that of the rational doctrine of nature—may be subdivided into two, physica rationalis[81] and psychologia rationalis.

[81] It must not be supposed that I mean by this appellation what is generally called physica general is, and which is rather mathematics than a philosophy of nature. For the metaphysic of nature is completely different from mathematics, nor is it so rich in results, although it is of great importance as a critical test of the application of pure understanding—cognition to nature. For want of its guidance, even mathematicians, adopting certain common notions—which are, in fact, metaphysical—have unconsciously crowded their theories of nature with hypotheses, the fallacy of which becomes evident upon the application of the principles of this metaphysic, without detriment, however, to the employment of mathematics in this sphere of cognition.

The fundamental idea of a philosophy of pure reason of necessity dictates this division; it is, therefore, architectonical—in accordance with the highest aims of reason, and not merely technical, or according to certain accidentally-observed similarities existing between the different parts of the whole science. For this reason, also, is the division immutable and of legislative authority. But the reader may observe in it a few points to which he ought to demur, and which may weaken his conviction of its truth and legitimacy.

In the first place, how can I desire an à priori cognition or metaphysic of objects, in so far as they are given à posteriori? and how is it possible to cognize the nature of things according to à priori principles, and to attain to a rational physiology? The answer is this. We take from experience nothing more than is requisite to present us with an object (in general) of the external or of the internal sense; in the former case, by the mere conception of matter (impenetrable and inanimate extension), in the latter, by the conception of a thinking being—given in the internal empirical representation, I think. As to the rest, we must not employ in our metaphysic of these objects any empirical principles (which add to the content of our conceptions by means of experience), for the purpose of forming by their help any judgements respecting these objects.

Secondly, what place shall we assign to empirical psychology, which has always been considered a part of metaphysics, and from which in our time such important philosophical results have been expected, after the hope of constructing an à priori system of knowledge had been abandoned? I answer: It must be placed by the side of empirical physics or physics proper; that is, must be regarded as forming a part of applied philosophy, the à priori principles of which are contained in pure philosophy, which is therefore connected, although it must not be confounded, with psychology. Empirical psychology must therefore be banished from the sphere of metaphysics, and is indeed excluded by the very idea of that science. In conformity, however, with scholastic usage, we must permit it to occupy a place in metaphysics—but only as an appendix to it. We adopt this course from motives of economy; as psychology is not as yet full enough to occupy our attention as an independent study, while it is, at the same time, of too great importance to be entirely excluded or placed where it has still less affinity than it has with the subject of metaphysics. It is a stranger who has been long a guest; and we make it welcome to stay, until it can take up a more suitable abode in a complete system of anthropology—the pendant to empirical physics.

The above is the general idea of metaphysics, which, as more was expected from it than could be looked for with justice, and as these pleasant expectations were unfortunately never realized, fell into general disrepute. Our Critique must have fully convinced the reader that, although metaphysics cannot form the foundation of religion, it must always be one of its most important bulwarks, and that human reason, which naturally pursues a dialectical course, cannot do without this science, which checks its tendencies towards dialectic and, by elevating reason to a scientific and clear self-knowledge, prevents the ravages which a lawless speculative reason would infallibly commit in the sphere of morals as well as in that of religion. We may be sure, therefore, whatever contempt may be thrown upon metaphysics by those who judge a science not by its own nature, but according to the accidental effects it may have produced, that it can never be completely abandoned, that we must always return to it as to a beloved one who has been for a time estranged, because the questions with which it is engaged relate to the highest aims of humanity, and reason must always labour either to attain to settled views in regard to these, or to destroy those which others have already established.

Metaphysic, therefore—that of nature, as well as that of ethics, but in an especial manner the criticism which forms the propædeutic to all the operations of reason—forms properly that department of knowledge which may be termed, in the truest sense of the word, philosophy. The path which it pursues is that of science, which, when it has once been discovered, is never lost, and never misleads. Mathematics, natural science, the common experience of men, have a high value as means, for the most part, to accidental ends—but at last also, to those which are necessary and essential to the existence of humanity. But to guide them to this high goal, they require the aid of rational cognition on the basis of pure conceptions, which, be it termed as it may, is properly nothing but metaphysics.

For the same reason, metaphysics forms likewise the completion of the culture of human reason. In this respect, it is indispensable, setting aside altogether the influence which it exerts as a science. For its subject-matter is the elements and highest maxims of reason, which form the basis of the possibility of some sciences and of the use of all. That, as a purely speculative science, it is more useful in preventing error than in the extension of knowledge, does not detract from its value; on the contrary, the supreme office of censor which it occupies assures to it the highest authority and importance. This office it administers for the purpose of securing order, harmony, and well-being to science, and of directing its noble and fruitful labours to the highest possible aim—the happiness of all mankind.

Chapter IV. The History of Pure Reason

This title is placed here merely for the purpose of designating a division of the system of pure reason of which I do not intend to treat at present. I shall content myself with casting a cursory glance, from a purely transcendental point of view—that of the nature of pure reason—on the labours of philosophers up to the present time. They have aimed at erecting an edifice of philosophy; but to my eye this edifice appears to be in a very ruinous condition.

It is very remarkable, although naturally it could not have been otherwise, that, in the infancy of philosophy, the study of the nature of God and the constitution of a future world formed the commencement, rather than the conclusion, as we should have it, of the speculative efforts of the human mind. However rude the religious conceptions generated by the remains of the old manners and customs of a less cultivated time, the intelligent classes were not thereby prevented from devoting themselves to free inquiry into the existence and nature of God; and they easily saw that there could be no surer way of pleasing the invisible ruler of the world, and of attaining to happiness in another world at least, than a good and honest course of life in this. Thus theology and morals formed the two chief motives, or rather the points of attraction in all abstract inquiries. But it was the former that especially occupied the attention of speculative reason, and which afterwards became so celebrated under the name of metaphysics.

I shall not at present indicate the periods of time at which the greatest changes in metaphysics took place, but shall merely give a hasty sketch of the different ideas which occasioned the most important revolutions in this sphere of thought. There are three different ends in relation to which these revolutions have taken place.

1. In relation to the object of the cognition of reason, philosophers may be divided into sensualists and intellectualists. Epicurus may be regarded as the head of the former, Plato of the latter. The distinction here signalized, subtle as it is, dates from the earliest times, and was long maintained. The former asserted that reality resides in sensuous objects alone, and that everything else is merely imaginary; the latter, that the senses are the parents of illusion and that truth is to be found in the understanding alone. The former did not deny to the conceptions of the understanding a certain kind of reality; but with them it was merely logical, with the others it was mystical. The former admitted intellectual conceptions, but declared that sensuous objects alone possessed real existence. The latter maintained that all real objects were intelligible, and believed that the pure understanding possessed a faculty of intuition apart from sense, which, in their opinion, served only to confuse the ideas of the understanding.

2. In relation to the origin of the pure cognitions of reason, we find one school maintaining that they are derived entirely from experience, and another that they have their origin in reason alone. Aristotle may be regarded as the head of the empiricists, and Plato of the noologists. Locke, the follower of Aristotle in modern times, and Leibnitz of Plato (although he cannot be said to have imitated him in his mysticism), have not been able to bring this question to a settled conclusion. The procedure of Epicurus in his sensual system, in which he always restricted his conclusions to the sphere of experience, was much more consequent than that of Aristotle and Locke. The latter especially, after having derived all the conceptions and principles of the mind from experience, goes so far, in the employment of these conceptions and principles, as to maintain that we can prove the existence of God and the immortality of the soul—both of them objects lying beyond the limits of possible experience—with the same force of demonstration, as any mathematical proposition.

3. In relation to method. Method is procedure according to principles. We may divide the methods at present employed in the field of inquiry into the naturalistic and the scientific. The naturalist of pure reason lays it down as his principle that common reason, without the aid of science—which he calls sound reason, or common sense—can give a more satisfactory answer to the most important questions of metaphysics than speculation is able to do. He must maintain, therefore, that we can determine the content and circumference of the moon more certainly by the naked eye, than by the aid of mathematical reasoning. But this system is mere misology reduced to principles; and, what is the most absurd thing in this doctrine, the neglect of all scientific means is paraded as a peculiar method of extending our cognition. As regards those who are naturalists because they know no better, they are certainly not to be blamed. They follow common sense, without parading their ignorance as a method which is to teach us the wonderful secret, how we are to find the truth which lies at the bottom of the well of Democritus.

Quod sapio satis est mihi, non ego curo Esse quod Arcesilas aerumnosique Solones. PERSIUS —Satirae, iii. 78-79.

is their motto, under which they may lead a pleasant and praiseworthy life, without troubling themselves with science or troubling science with them.

As regards those who wish to pursue a scientific method, they have now the choice of following either the dogmatical or the sceptical, while they are bound never to desert the systematic mode of procedure. When I mention, in relation to the former, the celebrated Wolf, and as regards the latter, David Hume, I may leave, in accordance with my present intention, all others unnamed. The critical path alone is still open. If my reader has been kind and patient enough to accompany me on this hitherto untravelled route, he can now judge whether, if he and others will contribute their exertions towards making this narrow footpath a high road of thought, that which many centuries have failed to accomplish may not be executed before the close of the present—namely, to bring Reason to perfect contentment in regard to that which has always, but without permanent results, occupied her powers and engaged her ardent desire for knowledge.