The Critique of Pure Reason

Preface to the Second Edition (continuación)

Now these sciences, if they can be termed rational at all, must contain elements of _à priori_ cognition, and this cognition may stand in a twofold relation to its object. Either it may have to _determine_ the conception of the object—which must be supplied extraneously, or it may have to _establish its reality_. The former is _theoretical_, the latter _practical_, rational cognition. In both, the _pure_ or _à priori_ element must be treated first, and must be carefully distinguished from that which is supplied from other sources. Any other method can only lead to irremediable confusion.

_Mathematics_ and _physics_ are the two theoretical sciences which have to determine their objects _à priori_. The former is purely _à priori_, the latter is partially so, but is also dependent on other sources of cognition.

In the earliest times of which history affords us any record, _mathematics_ had already entered on the sure course of science, among that wonderful nation, the Greeks. Still it is not to be supposed that it was as easy for this science to strike into, or rather to construct for itself, that royal road, as it was for logic, in which reason has only to deal with itself. On the contrary, I believe that it must have remained long—chiefly among the Egyptians—in the stage of blind groping after its true aims and destination, and that it was revolutionized by the happy idea of one man, who struck out and determined for all time the path which this science must follow, and which admits of an indefinite advancement. The history of this intellectual revolution—much more important in its results than the discovery of the passage round the celebrated Cape of Good Hope—and of its author, has not been preserved. But Diogenes Laertius, in naming the supposed discoverer of some of the simplest elements of geometrical demonstration—elements which, according to the ordinary opinion, do not even require to be proved—makes it apparent that the change introduced by the first indication of this new path, must have seemed of the utmost importance to the mathematicians of that age, and it has thus been secured against the chance of oblivion. A new light must have flashed on the mind of the first man (_Thales_, or whatever may have been his name) who demonstrated the properties of the _isosceles_ triangle. For he found that it was not sufficient to meditate on the figure, as it lay before his eyes, or the conception of it, as it existed in his mind, and thus endeavour to get at the knowledge of its properties, but that it was necessary to produce these properties, as it were, by a positive _à priori construction;_ and that, in order to arrive with certainty at _à priori_ cognition, he must not attribute to the object any other properties than those which necessarily followed from that which he had himself, in accordance with his conception, placed in the object.

A much longer period elapsed before _Physics_ entered on the highway of science. For it is only about a century and a half since the wise BACON gave a new direction to physical studies, or rather—as others were already on the right track—imparted fresh vigour to the pursuit of this new direction. Here, too, as in the case of mathematics, we find evidence of a rapid intellectual revolution. In the remarks which follow I shall confine myself to the _empirical_ side of natural science.

When GALILEI experimented with balls of a definite weight on the inclined plane, when TORRICELLI caused the air to sustain a weight which he had calculated beforehand to be equal to that of a definite column of water, or when STAHL, at a later period, converted metals into lime, and reconverted lime into metal, by the addition and subtraction of certain elements;[3] a light broke upon all natural philosophers. They learned that reason only perceives that which it produces after its own design; that it must not be content to follow, as it were, in the leading-strings of nature, but must proceed in advance with principles of judgement according to unvarying laws, and compel nature to reply its questions. For accidental observations, made according to no preconceived plan, cannot be united under a necessary law. But it is this that reason seeks for and requires. It is only the principles of reason which can give to concordant phenomena the validity of laws, and it is only when experiment is directed by these rational principles that it can have any real utility. Reason must approach nature with the view, indeed, of receiving information from it, not, however, in the character of a pupil, who listens to all that his master chooses to tell him, but in that of a judge, who compels the witnesses to reply to those questions which he himself thinks fit to propose. To this single idea must the revolution be ascribed, by which, after groping in the dark for so many centuries, natural science was at length conducted into the path of certain progress.

[3] I do not here follow with exactness the history of the experimental method, of which, indeed, the first steps are involved in some obscurity.

We come now to _metaphysics_, a purely speculative science, which occupies a completely isolated position and is entirely independent of the teachings of experience. It deals with mere conceptions—not, like mathematics, with conceptions applied to intuition—and in it, reason is the pupil of itself alone. It is the oldest of the sciences, and would still survive, even if all the rest were swallowed up in the abyss of an all-destroying barbarism. But it has not yet had the good fortune to attain to the sure scientific method. This will be apparent; if we apply the tests which we proposed at the outset. We find that reason perpetually comes to a stand, when it attempts to gain _à priori_ the perception even of those laws which the most common experience confirms. We find it compelled to retrace its steps in innumerable instances, and to abandon the path on which it had entered, because this does not lead to the desired result. We find, too, that those who are engaged in metaphysical pursuits are far from being able to agree among themselves, but that, on the contrary, this science appears to furnish an arena specially adapted for the display of skill or the exercise of strength in mock-contests—a field in which no combatant ever yet succeeded in gaining an inch of ground, in which, at least, no victory was ever yet crowned with permanent possession.

This leads us to inquire why it is that, in metaphysics, the sure path of science has not hitherto been found. Shall we suppose that it is impossible to discover it? Why then should nature have visited our reason with restless aspirations after it, as if it were one of our weightiest concerns? Nay, more, how little cause should we have to place confidence in our reason, if it abandons us in a matter about which, most of all, we desire to know the truth—and not only so, but even allures us to the pursuit of vain phantoms, only to betray us in the end? Or, if the path has only hitherto been missed, what indications do we possess to guide us in a renewed investigation, and to enable us to hope for greater success than has fallen to the lot of our predecessors?

It appears to me that the examples of mathematics and natural philosophy, which, as we have seen, were brought into their present condition by a sudden revolution, are sufficiently remarkable to fix our attention on the essential circumstances of the change which has proved so advantageous to them, and to induce us to make the experiment of imitating them, so far as the analogy which, as rational sciences, they bear to metaphysics may permit. It has hitherto been assumed that our cognition must conform to the objects; but all attempts to ascertain anything about these objects _à priori_, by means of conceptions, and thus to extend the range of our knowledge, have been rendered abortive by this assumption. Let us then make the experiment whether we may not be more successful in metaphysics, if we assume that the objects must conform to our cognition. This appears, at all events, to accord better with the _possibility_ of our gaining the end we have in view, that is to say, of arriving at the cognition of objects _à priori_, of determining something with respect to these objects, before they are given to us. We here propose to do just what COPERNICUS did in attempting to explain the celestial movements. When he found that he could make no progress by assuming that all the heavenly bodies revolved round the spectator, he reversed the process, and tried the experiment of assuming that the spectator revolved, while the stars remained at rest. We may make the same experiment with regard to the intuition of objects. If the intuition must conform to the nature of the objects, I do not see how we can know anything of them _à priori_. If, on the other hand, the object conforms to the nature of our faculty of intuition, I can then easily conceive the possibility of such an _à priori_ knowledge. Now as I cannot rest in the mere intuitions, but—if they are to become cognitions—must refer them, as _representations_, to something, as _object_, and must determine the latter by means of the former, here again there are two courses open to me. _Either_, first, I may assume that the conceptions, by which I effect this determination, conform to the object—and in this case I am reduced to the same perplexity as before; _or_ secondly, I may assume that the objects, or, which is the same thing, that _experience_, in which alone as given objects they are cognized, conform to my conceptions—and then I am at no loss how to proceed. For experience itself is a mode of cognition which requires understanding. Before objects, are given to me, that is, _à priori_, I must presuppose in myself laws of the understanding which are expressed in conceptions _à priori_. To these conceptions, then, all the objects of experience must necessarily conform. Now there are objects which reason _thinks_, and that necessarily, but which cannot be given in experience, or, at least, cannot be given _so_ as reason thinks them. The attempt to think these objects will hereafter furnish an excellent test of the new method of thought which we have adopted, and which is based on the principle that we only cognize in things _à priori_ that which we ourselves place in them.[4]

[4] This method, accordingly, which we have borrowed from the natural philosopher, consists in seeking for the elements of pure reason in that _which admits of confirmation or refutation by experiment_. Now the propositions of pure reason, especially when they transcend the limits of possible experience, do not admit of our making any experiment with their _objects_, as in natural science. Hence, with regard to those _conceptions_ and _principles_ which we assume _à priori_, our only course will be to view them from two different sides. We must regard one and the same conception, _on the one hand_, in relation to experience as an object of the senses and of the understanding, _on the other hand_, in relation to reason, isolated and transcending the limits of experience, as an object of mere thought. Now if we find that, when we regard things from this double point of view, the result is in harmony with the principle of pure reason, but that, when we regard them from a single point of view, reason is involved in self-contradiction, then the experiment will establish the correctness of this distinction.

This attempt succeeds as well as we could desire, and promises to metaphysics, in its first part—that is, where it is occupied with conceptions _à priori_, of which the corresponding objects may be given in experience—the certain course of science. For by this new method we are enabled perfectly to explain the possibility of _à priori_ cognition, and, what is more, to demonstrate satisfactorily the laws which lie _à priori_ at the foundation of nature, as the sum of the objects of experience—neither of which was possible according to the procedure hitherto followed. But from this deduction of the faculty of _à priori_ cognition in the first part of metaphysics, we derive a surprising result, and one which, to all appearance, militates against the great end of metaphysics, as treated in the second part. For we come to the conclusion that our faculty of cognition is unable to transcend the limits of possible experience; and yet this is precisely the most essential object of this science. The estimate of our rational cognition _à priori_ at which we arrive is that it has only to do with phenomena, and that things in themselves, while possessing a real existence, lie beyond its sphere. Here we are enabled to put the justice of this estimate to the test. For that which of necessity impels us to transcend the limits of experience and of all phenomena is the _unconditioned_, which reason absolutely requires in things as they are in themselves, in order to complete the series of conditions. Now, if it appears that when, on the one hand, we assume that our cognition conforms to its objects as things in themselves, _the unconditioned cannot be thought without contradiction_, and that when, on the other hand, we assume that our representation of things as they are given to us, does not conform to these things as they are in themselves, but that these objects, as phenomena, conform to our mode of representation, _the contradiction disappears:_ we shall then be convinced of the truth of that which we began by assuming for the sake of experiment; we may look upon it as established that the unconditioned does not lie in things as we know them, or as they are given to us, but in things as they are in themselves, beyond the range of our cognition.[5]

[5] This experiment of pure reason has a great similarity to that of the _Chemists_, which they term the experiment of _reduction_, or, more usually, the _synthetic_ process. The _analysis_ of the metaphysician separates pure cognition _à priori_ into two heterogeneous elements, viz., the cognition of things as phenomena, and of things in themselves. _Dialectic_ combines these again into harmony with the necessary rational idea of the unconditioned, and finds that this harmony never results except through the above distinction, which is, therefore, concluded to be just.

But, after we have thus denied the power of speculative reason to make any progress in the sphere of the supersensible, it still remains for our consideration whether data do not exist in _practical_ cognition which may enable us to determine the transcendent conception of the unconditioned, to rise beyond the limits of all possible experience from a _practical_ point of view, and thus to satisfy the great ends of metaphysics. Speculative reason has thus, at least, made room for such an extension of our knowledge: and, if it must leave this space vacant, still it does not rob us of the liberty to fill it up, if we can, by means of practical data—nay, it even challenges us to make the attempt.[6]

[6] So the central laws of the movements of the heavenly bodies established the truth of that which Copernicus, first, assumed only as a hypothesis, and, at the same time, brought to light that invisible force (Newtonian attraction) which holds the universe together. The latter would have remained forever undiscovered, if Copernicus had not ventured on the experiment—contrary to the senses but still just—of looking for the observed movements not in the heavenly bodies, but in the spectator. In this Preface I treat the new metaphysical method as a hypothesis with the view of rendering apparent the first attempts at such a change of method, which are always hypothetical. But in the Critique itself it will be demonstrated, not hypothetically, but apodeictically, from the nature of our representations of space and time, and from the elementary conceptions of the understanding.

This attempt to introduce a complete revolution in the procedure of metaphysics, after the _example_ of the geometricians and natural philosophers, constitutes the aim of the Critique of Pure Speculative Reason. It is a treatise on the method to be followed, not a system of the science itself. But, at the same time, it marks out and defines both the external boundaries and the internal structure of this science. For pure speculative reason has this peculiarity, that, in choosing the various objects of thought, it is able to define the limits of its own faculties, and even to give a complete enumeration of the possible modes of proposing problems to itself, and thus to sketch out the entire system of metaphysics. For, on the one hand, in cognition _à priori_, nothing must be attributed to the objects but what the thinking subject derives from itself; and, on the other hand, reason is, in regard to the principles of cognition, a perfectly distinct, independent unity, in which, as in an organized body, every member exists for the sake of the others, and all for the sake of each, so that no principle can be viewed, with safety, in one relationship, unless it is, at the same time, viewed in relation to the total use of pure reason. Hence, too, metaphysics has this singular advantage—an advantage which falls to the lot of no other science which has to do with _objects_—that, if once it is conducted into the sure path of science, by means of this criticism, it can then take in the whole sphere of its cognitions, and can thus complete its work, and leave it for the use of posterity, as a capital which can never receive fresh accessions. For metaphysics has to deal only with principles and with the limitations of its own employment as determined by these principles. To this perfection it is, therefore, bound, as the fundamental science, to attain, and to it the maxim may justly be applied:

Nil actum reputans, si quid superesset agendum.