Front Page Titles (by Subject) INTRODUCTION. - Kant’s Prolegomena and Metaphysical Foundations of Natural Science.
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INTRODUCTION. - Immanuel Kant, Kant’s Prolegomena and Metaphysical Foundations of Natural Science. 
Kant’s Prolegomena and Metaphysical Foundations of Natural Science, trans. with a Biography and Introduction by Ernest Belfort Bax (2nd revised edition) (London: George Bell and Sons, 1891).
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These Prolegomena are not designed for the use of pupils, but of future teachers, and even for the latter should serve not so much to regulate the exposition of an already existing science, as for the discovery of such a science.
There are scholars with whom the history of philosophy (ancient no less than modern) constitutes their own philosophy; for these the present Prolegomena are not written. They must wait till those, who are endeavouring to construct one out of the resources of Reason, have completed their work, and it will then be their turn to give an acount of what has already taken place. Otherwise nothing can be said which, in their opinion, has not been said before, and in fact this may pass as an infallible prophecy for all future time; inasmuch as the human understanding having speculated on countless subjects through so many centuries, in so many ways, it can scarcely fail that for every new idea an old one should be found having some affinity with it.
My purpose is, to convince all those who care to trouble themselves with metaphysics, that it is indispensably necessary for the present to suspend their work, to look upon all that is gone before as non-existent, and, above all things, first to propose the question “Whether such a thing as metaphysics be even possible at all?”
If it be a science, how comes it that it cannot like other sciences win for itself a universal and lasting recognition? If it be not one, how is it that under the semblance of a science it is ceaselessly boasting and holding out to the human understanding hopes that are never extinguished and never fulfilled? Something must be definitely decided respecting the nature of this assumed science, whether it be to demonstrate our knowledge or our ignorance; for it is impossible that it should remain longer on the same footing as heretofore. It seems well-nigh ridiculous, while every other science ceaselessly progresses, that this which is supposed to be wisdom itself, whose oracle every one interrogates, is continually turning round on the same spot, without moving a step in advance. Its votaries have also much decreased, and we do not see those who feel themselves strong enough to shine in other sciences, willing to risk their fame in this, where every one, ignorant though he be in all else, ventures upon a decided opinion, because forsooth in this sphere there is no certain weight and measure at hand by which to distinguish profundity from worthless jargon.
It is, however, nothing unheard of, after lengthened treatment of a science, when wonders are thought as to the progress made in it, that some one lets fall the question: Whether and how such a science is possible at all? For the human Reason is so fond of building, that it has many times reared up a lofty tower and afterwards pulled it down again, to see how its foundation was laid. It is never too late to become reasonable and wise; but it is always more difficult when the knowledge comes late to bring it into working order.
To ask, whether a science is possible, presupposes a doubt as to its reality. But such a doubt must offend all those whose whole fortune, perhaps, consists in this supposed treasure; any one who starts such a doubt may always make up his mind then for resistance on all sides. Some, in the proud consciousness of their old and therefore, as they think, legitimate possession, with their metaphysical compendiums in their hands, will look down upon it with contempt. Others, who never see anything anywhere that does not coincide with what they have elsewhere previously seen, will not understand it, and everything will remain for some time as though nothing at all had happened to prepare or to admit the hope of a near change.
At the same time, I may confidently predict that the self-thinking reader of these Prolegomena will not merely doubt his previous science, but in the end will be quite convinced, that there cannot exist such a science without the demands here made being satisfied, upon which its possibility rests, and that inasmuch as this has never happened, that there is as yet no such thing as metaphysics at all. But as notwithstanding the search after it can never lose its interest,1 because the interests of the universal human Reason are so intimately bound up with it, he will confess that a complete reform, or rather a new birth according to a plan hitherto quite unknown, is inevitable, however much it may be striven against for a time.
Since the attempts of Locke and Leibnitz, or rather since the first rise of metaphysics as far as its history will reach, no event has occurred that in view of the fortunes of the science could be more decisive than the attack made upon it by David Hume. He, indeed, threw no light upon this order of knowledge, but he struck a spark by which a light might have been kindled, had it touched a receptive substance, to have preserved and enlarged its glimmer.
Hume took for his starting-point, mainly, a single but important conception of metaphysics, namely, that of the connection of Cause and Effect (together with the derivative conceptions of Force and Action, &c.) and required of the Reason which professes to have given it birth a rigid justification of its right, to think, that something is so constructed that on its being posited something else is therewith necessarily also posited; for so much is contained in the conception of Cause. He proved irrefutably that it is quite impossible for the Reason à priori, out of mere conceptions, to cogitate this connection, since it involves necessity; but the problem nevertheless was not to be overlooked, how that, because something exists, something else must necessarily also exist, and thus how the conception of such a connection can be regarded as à priori. Hence he concluded that the Reason completely deceived itself with this conception, that it falsely claimed it as its own child, while it was nothing more than a bastard of the imagination, which, impregnated by experience, had brought certain presentations under the law of association, and had substituted a subjective necessity arising thence, i.e., from habit, for an objective one founded on insight. From this he concluded that the Reason possessed no faculty of cogitating such connections even in general, because its conceptions would then be mere inventions, and all its pretended à priori cognitions nothing but common experiences mislabelled; which is as much as to say, no such thing as metaphysics exists at all, and there is no possibility of its ever existing.1
However hasty and incorrect his conclusion may have been, it was at least based on investigation, and it would have been well worth while if the good heads of his time had united to solve the problem in the sense in which he had stated it, if as far as possible with happier results; the consequence of which must have been a speedy and complete reform of the science.
But the always unfavourable fate of metaphysics, willed that he should be understood by no one. It cannot be without feeling a certain regret that one sees how completely his opponents, Reid, Oswald, Beattie, and, lastly, Priestley, missed the point of his problem in taking that for granted which was precisely what he doubted, and on the other hand in proving with warmth, and in most cases great immodesty, what it had never entered his head to question, and as a result in so completely mistaking his reforming hint that everything remained in the same state as though nothing had happened. It was not the question whether the conception of Cause was correct and useful, and in view of the whole knowledge of Nature, indispensable, for upon this Hume had never cast a doubt, but whether it could be cogitated à priori by the Reason in such a manner as to constitute an inward truth independent of all experience, and therefore of a more extended use than that of being solely applied to the objects of experience; it was upon this that Hume desired enlightenment. The question was as to the origin of the idea, not as to its practical necessity in use; were the former ascertained, the conditions of its use and the extent in which it is valid would have been sufficiently obvious.
The opponents of this celebrated man, to have done the problem full justice, must have penetrated deeply into the nature of the Reason, in so far as it is occupied solely with pure thought, a thing which was inconvenient for them. They invented therefore a more convenient means, by which, without any insight, they might defy him, namely, the appeal to the common sense of mankind. It is indeed a great natural gift to possess, straightforward (or, as it has been recently called, plain) common sense. But it must be proved by deeds, by the thoughtfulness and rationality of what one thinks and says, and not by appealing to it as an oracle, when one has nothing wise to adduce in one’s justification. When insight and science are at a low ebb, then and not before to appeal to common sense is one of the subtle inventions of modern times, by which the emptiest talker may coolly confront the profoundest thinker and hold out against him. But so long as there is a small remnant of insight left, one will be cautious of clutching at this straw. And seen in its true light, the argument is nothing better than an appeal to the verdict of the multitude; a clamour before which the philosopher blushes, and the popular witling scornfully triumphs. But I should think that Hume can make as good claim to the possession of common sense as Beattie, and in addition, to something the latter certainly did not possess, namely, a critical Reason, to hold common sense within bounds in order not to let it overreach itself in speculations; or if we are merely concerned with the latter, not to require it to decide, seeing that it is incompetent to deal with matters outside its own axioms; for only in this way will it remain a healthy common sense. Chisel and hammer are quite sufficient to shape a piece of deal, but for copper-engraving an etching-needle is necessary. In the same way, common, no less than speculative understanding, is useful in its kind; the former when we have to do with judgments having an immediate bearing on experience, but the latter, where we have to judge, universally, out of mere conceptions, as for instance in metaphysics, where the self-styling (though often per antiphrasin) healthy understanding is capable of no judgment at all.
I readily confess, the reminder of David Hume was what many years ago first broke my dogmatic slumber, and gave my researches in the field of speculative philosophy quite a different direction. I was far enough removed from giving him an ear so far as his consequences were concerned, the latter resulting merely from his not having placed his problem fully before him, but only attacking a part of it, which, without taking the whole into consideration, could not possibly afford a solution. When one starts from a well-founded, though undeveloped, idea that a predecessor has left, one may well hope, by increased reflection, to bring it further than was possible for the acute man one has to thank for the original sparks of its light.
First of all, I tried whether Hume’s observation could not be made general, and soon found that the conception of the connection of cause and effect was not by a long way the only one by which the understanding cogitates à priori the connections of things, but that metaphysics consists entirely of such. I endeavoured to ascertain their number, and as I succeeded in doing this to my satisfaction, namely, out of a single principle, I proceeded to the deduction of these conceptions, which I was now assured could not, as Hume had pretended, be derived from experience but must have originated in the pure understanding. This deduction, that seemed impossible to my acute predecessor, that had not even occurred to any one except him, although every one unconcernedly used the conception (without asking on what its objective validity rested); this, I say, was the most difficult problem that could ever be undertaken in the interests of metaphysics, and the worst of it was, that metaphysics, so far as it anywhere exists at present, could not afford me the least help, because the above deduction had in the first place to make metaphysics possible. Having now succeeded in the solution of Hume’s problem, not in one particular case only, but in respect of the whole capacity of the pure Reason, I could at least more surely, though still only by slow steps, determine the whole range of the pure Reason, in its limits as well as in its content, completely according to universal principles, which was what metaphysics required, in order to construct its system on an assured plan.
I am afraid, however, lest the carrying out of the problem of Hume in its greatest possible development (namely, in the Critique of the Pure Reason) should fare as the problem itself fared when it was first stated. It will be falsely judged, because it is misunderstood; it will be misunderstood, because people, though they may care to turn over the leaves of the book, will not care to think it out; and they will be unwilling to expend this trouble upon it because the work is dry, obscure, and opposed to all accustomed conceptions, besides being diffuse. But I must confess, it was quite unexpected for me to hear from a philosopher complaints as to its want of popularity, entertainingness, and agreeable arrangement, when the question was of a branch of knowledge highly prized and indispensable to humanity, and which cannot be treated otherwise than according to the most strict rules of scholastic precision; whereby popularity may indeed follow in time, but can never be expected at the commencement. As regards a certain obscurity, however, arising partly from the diffuseness of the plan, in consequence of which the main points of the investigation are not so readily grasped, the grievance must be admitted, and this it is the task of the present Prolegomena to remove.
The above work, which presents the capacity of the pure Reason in its whole range and boundaries, always remains the foundation to which the Prolegomena are only preparatory; for the Critique must, as science, stand complete and systematic even down to the smallest detail, before we can so much as think of the rise of metaphysics, or even allow ourselves the most distant hope in this direction.
We have been long accustomed to see old and worn-out branches of knowledge receive a new support, by being taken out of their former coverings, and suited with a systematic garment according to our own approved style, but under new titles; and the great majority of readers will expect nothing different from our Critique. But these Prolegomena will convince him that it is quite a new science, of which no one previously had had the smallest conception, of which even the idea was unknown, and with reference to which all hitherto received knowledge was unavailable, with the exception of the hint afforded by Hume’s doubt. But Hume never dreamt of a possible formal science of this nature, and in order to land his ship in safety, ran it aground on the shore of scepticism, where it might lie and rot; instead of which, it is my purpose to furnish a pilot, who, according to certain principles of seamanship, derived from a knowledge of the globe, and supplied with a complete map and compass, may steer the ship with safety wherever it seems good to him.
In a new science, which is wholly isolated and single of its kind, we should achieve nothing were we to start with the prejudice that we could judge of things by means of our previously acquired knowledge, which is precisely what has first to be called in question. For were we to do this, we should only fancy we saw everywhere what we had already known, the expressions, having a similar sound, only that all would appear utterly metamorphosed, senseless and unintelligible, because we should have as a foundation our own notions, made by long habit a second nature, instead of the author’s. But the diffuseness of the work, founded as it is on science (of which an unavoidable dryness and scholastic precision are characteristics) rather than on style, however advantageous it may be to the subject, is undoubtedly disadvantageous to the book.
It is indeed not given to every one to write as subtly and at the same time as fascinatingly as David Hume, or as profoundly and as elegantly as Moses Mendelssohn; but I flatter myself I might have rendered my style popular, if I had only had to sketch a plan, and to leave its completion to others, and not had the well-being of the science, with which I had been so long occupied, so much at heart; for it requires considerable endurance and not a little self-denial to choose a late but enduring fame, in preference to the allurement of a speedy and favourable reception.
Plan-making is often a luxurious and pretentious mental occupation, whereby the reputation of a creative genius is acquired by demanding what one cannot achieve oneself, censuring what one cannot improve, and proposing what one does not know where to find. But to a thorough plan of the general Critique of the Reason something more is necessary, as may be well supposed, if it is not to be, as usual, a mere declamation of pious wishes. For pure Reason is so isolated, and in itself so intimately connected a sphere, that no part of it can be touched upon without affecting the rest. We can accomplish nothing, therefore, without determining the position and influence of each part with regard to the others, because there is nothing external to it by which our judgment can be corrected as to its inner character. The validity and use of every part depends upon the relations in which it stands toward the rest witin the Reason, and as in the construction of an organised body, the purpose of each member can only be deduced from a complete conception of the whole. It may therefore be said of such a critique that it is never reliable, unless it be quite complete, down to the least of the elements of pure Reason; and that in the sphere of this faculty, one must determine and expound either everything or nothing.
Yet although a mere plan, if it preceded the critique, would be incomprehensible, unreliable and useless, it is so much the more useful when it follows it. For one is then in a position to view the whole, to test the main points upon which the science rests piecemeal, and to render the style better than was possible on the first execution of the work.
The following is such a plan, which as the work is complete may be presented in an analytical manner, whereas the work itself was obliged to be constructed throughout on a synthetic method, in order that the science might exhibit all its articulations in there natural connection as the organisation of a special faculty of knowledge. Should, on the other hand, any one find this plan, put forward by me as Prolegomena to any future system of metaphysics, itself obscure, he must bear in mind that it is not necessary for every one to study metaphysics; that there is much talent, perfectly adequate to the investigation of thorough and even deep sciences, lying more in the region of intuition, which is unsuccessful in a species of research based solely on abstract conceptions, and that, in such a case, mental abilities should be turned in another direction. But he who undertakes to judge a system of metaphysics or to construct one, must in every way satisfy the demands that will here be made. It may so happen, either that he accepts my solution, or that he utterly refutes it and offers another in its stead—evade it, he cannot; and that, finally, the so-much decried obscurity (though a frequent covering for indolence and stupidity) may have its uses, since those who in respect of other sciences maintain a judicious silence, in questions of metaphysics speak and decide in a dictatorial tone, because here their ignorance does not distinctly clash with the knowledge of other people, though not the less with the axioms of a sound criticism; of which one may say, ignavum fucos, pecus a prœsepibus arcent. Virg.’ (they keep off, from the hives, the lazy swarm of drones).
[1 ]“Rusticus expectat, dum defluat amnis, at ille Labitur et labetur in omne volubilis ævum.” (Horat.) “The peasant waits till the river has flowed past, but it flows, and will continue to flow, to all eternity.”
[1 ]At the same time, Hume called this destructive philosophy itself metaphysics, and attached a high value to it. “Metaphysics and morals,” he says (Essays, Part IV.), “are the most important branches of science; mathematics and natural philosophy have not half the same value.” But the acute man considered here only the negative uses, that the moderation of the exaggerated claims of the speculative reason would have, in putting an end to the many endless and vexatious disputes that perplex mankind; but at the same time he lost sight of the positive evils that would ensue from the removal of the most important expectations of the Reason, which it can alone place before the will as the highest goal of all its strivings.