Critique of Pure Reason

by Immanuel Kant

  The real reason why apagogical proofs are so much employed in different sciences, seems to be this. If the grounds from which some knowledge is to be derived are too numerous or too deeply hidden, one tries whether they may not be reached through their consequences. Now it is quite true that this modus ponens, that is, this inferring of the truth of some knowledge from the truth of its consequences, is only permitted, if all possible consequences flowing from it are true. In that case they have only one possible ground, which therefore is also the true one. This procedure, however, is impracticable, because to discover all possible consequences of any given proposition exceeds our powers. Nevertheless, this mode of arguing is employed, though under a certain indulgence, whenever something is to be established as a hypothesis only, in which case a conclusion, according to analogy, is admitted, namely, that if as many consequences as one has tested agree with an assumed ground, all others will also agree with it. To change in this way a hypothesis into a demonstrated truth, is clearly impossible. The modus tollens of reasoning, from consequences to their grounds, is not only perfectly strict, but also extremely easy. For if one single false consequence only can be drawn from a proposition, that proposition is wrong. Instead, therefore, of examining, for the sake of an ostensive proof, the whole series of grounds that may lead us to the truth of a cognition by means of a perfect insight into its possibility, we have only to prove that one single consequence, resulting from the opposite, is false, in order to show that the opposite itself is false, and therefore the cognition, which we had to prove, true.

  This apagogical method of proof, however, is admissible in those sciences only where it is impossible to foist the subjective elements of our representations into the place of what is objective, namely, the knowledge of that which exists in the object. When this is not impossible, it must often happen that the opposite of any proposition contradicts the subjective conditions of thought only, but not the object itself, or, that both propositions contradict each other under a subjective condition, which is mistaken as objective, so that, as the condition is false, both may be false, without our being justified in inferring the truth of the one from the falseness of the other.

  In mathematics such subreptions are impossible; and it is true, therefore, that the apagogical proof has its true place there. In natural science, in which everything is based on empirical intuitions, that kind of subreption can generally be guarded against by a repeated comparison of observations; but even thus, this mode of proof is of little value there. The transcendental endeavours of pure reason, however, are all made within the very sphere of dialectical illusion, where what is subjective presents itself, nay, forces itself upon reason in its premisses as objective: Here, therefore, it can never be allowed, with reference to synthetical propositions, to justify one's assertions by refuting their opposite. For, either this refutation may be nothing but the mere representation of the conflict of the opposite opinion with the subjective conditions under which our reason could alone comprehend it, and this would be of no avail for rejecting the proposition itself,—(thus we see, for instance, that the unconditioned necessity of the existence of a Being cannot possibly be comprehended by us, which subjectively bars every speculative proof of a necessary Supreme Being but by no means, the possibility of such a Being by itself),—or, on the other hand, it may be that both the affirmative and the negative party have been deceived by the transcendental illusion, and base their arguments on an impossible concept of an object. In that case the rule applies, non entis nulla sunt praedicata, that is, everything that has been asserted with regard to an object, whether affirmatively or negatively, is wrong, and we cannot therefore arrive apagogically at the knowledge of truth by the refutation of its opposite. If, for example, we assume that the world of sense is given by itself in its totality, it is wrong to conclude that it must be either infinite in space, or finite and limited; for either is wrong, because phenomena (as mere representations) which nevertheless are to be things by themselves (as objects) are something impossible, and the infinitude of this imaginary whole, though it might be unconditioned, would (because everything in phenomena is conditioned) contradict that very unconditioned quantity which is presupposed in its concept.

  The apagogical mode of proof is also the blind by which the admirers of our dogmatical philosophy have always been deceived. It may be compared to a prizefighter who is willing to prove the honour and the incontestable rights of his adopted party by offering battle to all and every one who should dare to doubt them. Such brawling, however, settles nothing, but only shows the respective strength of the two parties, and even this on the part of those only who take the offensive. The spectators, seeing that each party is alternately conqueror and con- quered, are often led to regard the very object of the dispute with a certain amount of scepticism. In this, however, they are wrong, and it is sufficient to remind them of non defensoribus istis tempus eget. It is absolutely necessary that every one should plead his cause directly by means of a legitimate proof based on a transcendental deduction of the grounds of proof. Thus only can we see what he may have to say himself in favour of his own claims of reason. If his opponent relies on subjective grounds only, it is easy, no doubt, to refute him; but this does not benefit the dogmatist, who generally depends quite as much on the subjective grounds of his judgment, and can be quite as easily driven into a corner by his opponent. If, on the contrary, both parties employ only the direct mode of proof, they will either themselves perceive the difficulty, nay, the impossibility of finding any title for their assertions, and appeal in the end to prescription only, or, our criticism will easily discover the dogmatical illusion, and compel pure reason to surrender its exaggerated pretensions in the sphere of speculative thought, and to retreat within the limits of its own domain,—that of practical principles.

  1 I am well aware that in the language of the schools, discipline is used as synonymous with instruction. But there are so many cases in which the former term, in the sense of restraint, is carefully distinguished from the latter in the sense of teaching, and the nature of things makes it so desirable to preserve the only suitable expressions for that distinction, that I hope that the former term may never be allowed to be used in any but a negative meaning.

  2 In the concept of cause I really pass beyond the empirical concept of an event, but not to the intuition which represents the concept of cause in concreto, but to the conditions of time in general, which in experience might be found in accordance with the concept of cause. I therefore proceed here, according to concepts only, but cannot proceed by means of the construction of concepts, because the concept is only a rule for the synthesis of perceptions, which are not pure intuitions, and therefore cannot be given a priori.

  3 Completeness means clearness and sufficiency of predicates; limits mean precision, no more predicates being given than belong to the complete concept; in its primary character means that the determination of these limits is not derived from anything else, and therefore in need of any proof, because this would render the so-called definition incapable of standing at the head of all the judgments regarding its object.

  4 Philosophy swarms with faulty definitions, particularly such as contain some true elements of a definition, but not all. If, therefore, it were impossible to use a concept until it had been completely defined, philosophy would fare very ill. As, however, we may use a definition with perfect safety, so far at least as the elements of the analysis will carry us, imperfect definitions also, that is, propositions which are not yet properly definitions, but are yet true, and, therefore, approximations to a definition, may be used with great advantage. In mathematics definitions belong ad esse, in philosophy ad melius esse. It is desirable, but it is extremely difficult to construct a proper definition. Jurists are without a definition of right to the present day.

  5 Read reine instead of keine.

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  Method of Transcendentalism

  Chapter II

&n
bsp; The Canon of Pure Reason

  It is humiliating, no doubt, for human reason that it can achieve nothing by itself, nay, that it stands in need of a discipline to check its vagaries, and to guard against the illusions arising from them. But, on the other hand, it elevates reason and gives it self-confidence, that it can and must exercise that discipline itself, and allows no censorship to any one else. The bounds, moreover, which it is obliged to set to its own speculative use check at the same time the sophistical pretensions of all its opponents, and thus secure everything that remains of its formed exaggerated pretensions against every possible attack. The greatest and perhaps the only advantage of all philosophy of pure reason seems therefore to be negative only; because it serves, not as an organon for the extension, but as a discipline for the limitation of its domain, and instead of discovering truth, it only claims the modest merit of preventing error.

  Nevertheless, there must be somewhere a source of positive cognitions which belong to the domain of pure reason, and which perhaps, owing to some misunderstanding only, may lead to error, while they form in reality the true goal of all the efforts of reason. How else could we account for that inextinguishable desire to gain a footing by any means somewhere beyond the limits of experience? Reason has a presentiment of objects which possess a great interest for it. It enters upon the path of pure speculation in order to approach them, but they fly before it. May we not suppose that on the only path which is still open to it, namely, that of its practical employments, reason may hope to meet with better success?

  I understand by a canon a system of principles a priori for the proper employment of certain faculties of knowledge in general. Thus general logic, in its analytical portion, is a canon for the understanding and reason in general, but only so far as the form is concerned, for it takes no account of any contents. Thus we saw that the transcendental analytic is the canon of the pure understanding, and that it alone is capable of true synthetical knowledge a priori. When no correct use of a faculty of knowledge is possible, there is no canon, and as all synthetical knowledge of pure reason in its speculative employment is, according to all that has been hitherto said, totally impossible, there exists no canon of the speculative employment of reason (for that employment is entirely dialectical), but all transcendental logic is, in this respect, disciplinary only. Consequently, if there exists any correct use of pure reason at all, and, therefore, a canon relating to it, that canon will refer not to the speculative, but to the practical use of reason, which we shall now proceed to investigate.

  The Canon of Pure Reason

  First Section

  Of the Ultimate Aim of the Pure Use of our Reason

  Reason is impelled by a tendency of its nature to go beyond the field of experience, and to venture in its pure employment and by means of mere ideas to the utmost limits of all knowledge; nay, it finds no rest until it has fulfilled its course and established an independent and systematic whole of all knowledge. The question is, whether this endeavour rests on the speculative, or rather, exclusively on the practical interests of reason?

  I shall say nothing at present of the success which has attended pure reason in its speculative endeavours, and only ask which are the problems, the solution of which forms its ultimate aim (whether that object be really reached or not), and in relation to which all other problems are only means to an end. These highest aims must again, according to the nature of reason, possess a certain unity in order to advance by their union that interest of humanity which is second to no other.

  The highest aim to which the speculation of reason in its transcendental employment is directed comprehends three objects: the freedom of the will, the immortality of the soul, and the existence of God. The purely speculative interest of reason in every one of these three questions is very small, and, for its sake alone, this fatiguing and ceaseless labour of transcendental investigation would hardly have been undertaken, because whatever discoveries may be made, they could never be used in a way that would be advantageous in concreto, that is, in the investigation of nature.

  Our will may be free, but this would only refer to the intelligible cause of our volition. With regard to the phenomena in which that will manifests itself, that is, our actions, we have to account for them (according to an inviolable maxim without which reason could not be employed for empirical purposes at all), in no other way than for all other phenomena of nature, that is, according to her unchangeable laws.

  Secondly, the spiritual nature of the soul, and with it its immortality, may be understood by us, yet we could not base upon this any explanation, either with regard to the phenomena of this life, or the peculiar nature of a future state, because our concept of an incorporeal nature is purely negative and does not expand our knowledge in the least, nor does it offer any fit material for drawing consequences, except such as are purely fictitious, and could never be countenanced by philosophy.

  Thirdly, even admitting that the existence of a highest intelligence had been proved, we might, no doubt, use it in order to make the design in the constitution of the world and its order in general intelligible, but we should never be justified in deriving from it any particular arrangement, or disposition, or in boldly inferring it where it cannot be perceived. For it is a necessary rule for the speculative employment of reason, never to pass by natural causes, and, abandoning what we may learn from experience, to derive something which we know, from something which entirely transcends all our knowledge.

  In one word, these three propositions remain always transcendent for speculative reason, and admit of no immanent employment, that is, an employment admissible for objects of experience, and therefore of some real utility to ourselves, but are by themselves entirely valueless and yet extremely difficult exertions of our reason.

  If, therefore, these three cardinal propositions are of no use to us, so far as knowledge is concerned, and are yet so strongly recommended to us by our reason, their true value will probably be connected with our practical interests only.

  I call practical whatever is possible through freedom. When the conditions of the exercise of our free-will are empirical, reason can have no other but a regulative use, serving only to bring about the unity of empirical laws. Thus, for instance, in the teaching of prudence, the whole business of reason consists in concentrating all the objects of our desires in one, namely, happiness, and in co-ordinating the means for obtaining it. Reason, therefore, can give us none but pragmatic laws of free action for the attainment of the objects recommended to us by the senses, and never pure laws, determined entirely a priori. Pure practical laws, on the contrary, the object of which is given by reason entirely a priori, and which convey commands, not under empirical conditions, but absolutely, would be products of pure reason. Such are the moral laws, and these alone, therefore, belong to the sphere of the practical use of reason, and admit of a canon.

  All the preparations of reason, therefore, in what may be called pure philosophy, are in reality directed to those three problems only. These themselves, however, have a still further object, namely, to know what ought to be done, if the will is free, if there is a God, and if there is a future world. As this concerns our actions with reference to the highest aim of life, we see that the last intention of nature in her wise provision was really, in the constitution of our reason, directed to moral interests only.

  We must be careful, however, lest, as we are now considering a subject which is foreign to transcendental philosophy,1 we should lose ourselves in episodes, and injure the unity of the system, while on the other side, if we say too little of this new matter, there might be a lack of clearness and persuasion. I hope to avoid both dangers by keeping as close as possible to what is transcendental, and by leaving entirely aside what may be psychological, that is, empirical in it.

  I have, therefore, first to remark that for the present I shall use the concept of freedom in its practical meaning only, taking no account of the other concept of freedom in its transcendental meanin
g, which cannot be presupposed empirically as an explanation of phenomena, but is itself a problem of reason and has been disposed of before. A will is purely animal (arbitrium brutum) when it is determined by nothing but sensuous impulses, that is, pathologically. A will, on the contrary, which is independent of sensuous impulses, and can be determined therefore by motives presented by reason alone, is called Free-will (arbitrium liberum), and everything connected with this, whether as cause or effect, is called practical. Practical freedom can be proved by experience. For human will is not determined by that only which excites, that is, immediately affects the senses; but we possess the power to overcome the impressions made on the faculty of our sensuous desires, by representing to ourselves what, in a more distant way, may be useful or hurtful. These considerations of what is desirable with regard to our whole state, that is, of what is good and useful, are based entirely on reason. Reason, therefore, gives laws which are imperatives, that is, objective laws of freedom, and tell us what ought to take place, though perhaps it never does take place, differing therein from the laws of nature, which relate only to what does take place. These laws of freedom, therefore, are called practical laws.

  Whether reason in prescribing these laws is not itself determined by other influences, and whether what, in relation to sensuous impulses, is called freedom, may not, with regard to higher and more remote causes, be nature again, does not concern us while engaged in these practical questions, and while demanding from reason nothing but the rule of our conduct. It is a purely speculative question which, while we are only concerned with what we ought or ought not to do, may well be left aside. We know practical freedom by experience as one of the natural causes, namely, as a causality of reason in determining the will, while transcendental freedom demands the independence of reason itself (with reference to its causality in beginning a series of phenomena) from all determining causes in the world of sense, thus running counter, as it would seem, to the law of nature and therefore to all possible experience, and remaining a problem. Reason, however, in its practical employment has nothing to do with this problem, so that there remain but two questions in a canon of pure reason which concern the practical interest of pure reason, and with regard to which a canon of their employment must be possible, namely: Is there a God? Is there a future life? The question of transcendental freedom refers to speculative knowledge only, and may be safely left aside as quite indifferent when we are concerned with practical interests. A sufficient discussion of it may be found in the antinomy of pure reason.