Our reason is not to be considered as an indefinitely extended plain, the limits of which are known in a general way only, but ought rather to be compared to a sphere the radius of which may be determined from the curvature of the arc of its surface (corresponding to the nature of synthetical propositions a priori), which enables us likewise to fix the extent and periphery of it with perfect certainty. Outside that sphere (the field of experience) nothing can become an object to our reason, nay, questions even on such imaginary objects relate to the subjective principles only for a complete determination of all the relations which may exist between the concepts of the understanding within that sphere.
It is a fact that we are in possession of different kinds of synthetical knowledge a priori, as shown by the principles of the understanding which anticipate experience. If anybody finds it quite impossible to understand the possibility of such principles, he may at first have some doubts as to whether they really dwell within us a priori; but he cannot thus, by the mere powers of the understanding, prove their impossibility, and declare all the steps which reason takes under their guidance as null and void. All he can say is that, if we could understand their origin and genuineness, we should be able to determine the extent and limits of our reason, and that, until that is done, all the assertions of reason are made at random. And in this way a complete scepticism with regard to all dogmatical philosophy, which is not guided by a criticism of reason, is well grounded, though we could not therefore deny to reason such further advance, after the way has once been prepared and secured on firmer ground. For all these concepts, nay, all the questions which pure reason places before us, have their origin, not in experience, but in reason itself, and must therefore be capable of being solved and tested as to their validity or invalidity. Nor are we justified, while pretending that the solution of these problems is really to be found in the nature of things, to decline their consideration and further investigation, under the pretext of our weakness, for reason alone begets all these ideas by itself, and is bound therefore to give an account of their validity or their dialectical vanity.
All sceptical polemic should properly be directed against the dogmatist only who, without any misgivings about his own fundamental objective principles, that is, without criticism, continues his course with undisturbed gravity, and should be intended only to unsettle his brief and to bring him thus to a proper self-knowledge. With regard to what we know or what we cannot know, that polemic is of no consequence whatever. All the unsuccessful dogmatical attempts of reason are facta, and it is always useful to submit them to the censura of the sceptic. But this can decide nothing as to the expectations of reason in her hopes and claims of a better success in future attempts; and no mere censura can put an end to the disputes regarding the rights of human reason.
Hume is, perhaps, the most ingenious of all sceptics, and without doubt the most important with regard to the influence which the sceptical method may exercise in awakening reason to a thorough examination of its rights. It will therefore be worth our while to make clear to ourselves the course of his reasoning and the errors of an intelligent and estimable man, who at the outset of his enquiries was certainly on the right track of truth.
Hume was probably aware, though he never made it quite clear to himself, that in judgments of a certain kind we pass beyond our concept of the object. I have called this class of judgments synthetical. There is no difficulty as to how I may, by means of experience, pass beyond the concept which I have hitherto had. Experience is itself such a synthesis of perceptions through which a concept, which I have by means of one perception, is increased by means of other perceptions. But we imagine that we are able also a priori to pass beyond our concept and thus to enlarge our knowledge. This we attempt to do either by the pure understanding, in relation to that which can at least be an object of experience, or even by means of pure reason, in relation to such qualities of things, or even the existence of such things, as can never occur in experience. Hume in his scepticism did not distinguish between these two kinds of judgments as he ought to have done, but regarded this augmentation of concepts by themselves, and, so to say, the spontaneous generation of our understanding (and of our reason), without being impregnated by experience, as perfectly impossible. Considering all principles a priori as imaginary, he arrived at the conclusion that they were nothing but a habit arising from experience and its laws; that they were therefore merely empirical, that is, in themselves, contingent rules to which we wrongly ascribe necessity and universality. In order to establish this strange proposition, he appealed to the generally admitted principle of the relation between cause and effect. For as no faculty of the understanding could lead us from the concept of a thing to the existence of something else that should follow from it universally and necessarily, he thought himself justified in concluding that, without experience, we have nothing that could augment our concept and give us a right to form a judgment that extends itself a priori. That the light of the sun which shines on the wax should melt the wax and at the same time harden the clay, no understanding, he maintained, could guess from the concepts which we had before of these things, much less infer, according to a law, experience only being able to teach us such a law. We have seen, on the contrary, in the transcendental logic that, though we can never pass immediately beyond the content of a concept that is given us, we are nevertheless able, entirely a priori, but yet in reference to something else, namely, possible experience, to know the law of its connection with other things. If, therefore, wax, which was formerly hard, melts, I can know a priori that something else must have preceded (for instance the heat of the sun) upon which this melting has followed according to a permanent law, although without experience I could never know a priori definitely either from the effect the cause, or from the cause the effect. Hume was therefore wrong in inferring from the mere contingency of our being determined according to the law of causality, the contingency of that law itself, and he mistook our passing beyond the concept of a thing to some possible experience (which is entirely a priori and constitutes the objective reality of it) for the synthesis of the objects of real experience which, no doubt, is always empirical. He thus changed a principle of affinity which resides in the understanding and predicates necessary connection, into a rule of association residing in the imitative faculty of imagination, which can only represent contingent, but never objective connections.
The sceptical errors of that otherwise singularly acute thinker arose chiefly from a defect, which he shared, however, in common with all dogmatists, namely, of not having surveyed systematically all kinds of synthesis a priori of the understanding. For in doing this he would, without mentioning others, have discovered, for instance, the principle of permanency as one which, like causality, anticipates experience. He would thus have been able also to fix definite limits to the understanding in its attempts at expansion a priori and to pure reason. He only narrows the sphere of our understanding, without definitely limiting it, and produces a general mistrust, but no definite knowledge of that ignorance which to us is inevitable. He only subjects certain principles of the understanding to his censura, but does not place the understanding, with reference to all its faculties, on the balance of criticism. He is not satisfied with denying to the understanding what in reality it does not possess, but goes on to deny to it all power of expanding a prior, though he has never really tested all its powers. For this reason, what always defeats scepticism has happened to Hume also, namely, that he himself becomes subject to scepticism, because his objections rest on facts only which are contingent, and not on principles which alone can force a surrender of the right of dogmatical assertion.
As, besides this, he does not sufficiently distinguish between the well-grounded claims of the understanding and the dialectical pretensions of reason, against which, however, his attacks are chiefly directed, it so happens that reason, the peculiar tendency of which has not in the least been destroyed, but only checked, does not at all consider
itself shut out from its attempts at expansion, and can never be entirely turned away from them, although it may be punished now and then. Mere attacks only provoke counter attacks, and make us more obstinate in enforcing our own views. But a complete survey of all that is really our own, and the conviction of a certain though a small possession, make us perceive the vanity of higher claims, and induce us, after surrendering all disputes, to live contentedly and peacefully within our own limited, but undisputed domain.
These sceptical attacks are not only dangerous, but even destructive to the uncritical dogmatist who has not measured the sphere of his understanding, and has not, therefore, determined, according to principles, the limits of his own possible knowledge, and does not know beforehand how much he is really able to achieve, but thinks that he is able to find all this out by a purely tentative method. For if he has been found out in one single assertion of his, which he cannot justify, or the fallacy of which he cannot evolve according to principles, suspicion falls on all his assertions, however plausible they may appear.
And thus the sceptic is the true schoolmaster to lead the dogmatic speculator towards a sound criticism of the understanding and of reason. When he has once been brought there, he need fear no further attacks, for he has learnt to distinguish his own possession from that which lies completely beyond it, and on which he can lay no claim, nor become involved in any disputes regarding it. Thus the sceptical method, though it cannot in itself satisfy with regard to the problems of reason, is nevertheless an excellent preparation in order to awaken its circumspection, and to indicate the true means whereby the legitimate possessions of reason may be secured against all attacks.
Discipline of Pure Reason
Section III
The Discipline of Pure Reason with Regard to Hypotheses
As then the criticism of our reason has at last taught us so much at least, that with its pure and speculative use we can arrive at no knowledge at all, would not this seem to open a wide field for hypotheses, as, where we cannot assert with certainty, we are at all events at liberty to form guesses and opinions?
If the faculty of imagination is not simply to indulge in dreams, but to invent and compose under the strict surveillance of reason, it is necessary that there should always be something perfectly certain, and not only invented or resting on opinion, and that is the possibility of the object itself. If that is once given, it is then allowable, so far as its reality is concerned, to have recourse to opinion, which opinion, however, if it is not to be utterly groundless, must be brought in connection with what is really given and therefore certain, as its ground of explanation. In that case, and in that case only, can we speak of an hypothesis.
As we cannot form the least conception of the possibility of a dynamical connection a priori, and as the categories of the pure understanding are not intended to invent any such connection, but only, when it is given in experience, to understand it, we cannot by means of these categories invent one single object as endowed with a new quality not found in experience, or base any permissible hypothesis on such a quality; otherwise we should be supplying our reason with empty chimeras, and not with concepts of things. Thus it is not permissible to invent any new and original powers, as, for instance, an understanding capable of perceiving objects without the aid of the senses; or a force of attraction without any contact; a new kind of substances that should exist, for instance, in space, without being impenetrable, and consequently, also, any connection of substances, different from that which is supplied by experience; no presence, except in space, no duration, except in time. In one word, our reason can only use the conditions of possible experience as the conditions of the possibility of things; it cannot invent them independently, because such concepts, although not self-contradictory, would always be without an object.
The concepts of reason, as was said before, are mere ideas, and it is true that they have no object corresponding to them in experience; but they do not, for all that, refer to purely imaginary objects, which are supposed to be possible. They are purely problematical, in order to supply (as heuristic fictions) regulative principles for the systematical employment of the understanding in the sphere of experience. If they are not that, they would become mere fictions the possibility of which is quite indemonstrable, and which, therefore, can never be employed as hypotheses for the explanation of real phenomena. It is quite permissible to represent the soul to ourselves as simple, in order, according to this idea, to use the complete and necessary unity of all the faculties of the soul, although we cannot understand it in concreto, as the principle of all our enquiries into its internal phenomena. But to assume the soul as a simple substance (which is a transcendent concept) would be a proposition, not only indemonstrable (this is the case with several physical hypotheses), but purely arbitrary and rash: because the simple can never occur in any experience, and if by substance we understand the permanent object of sensuous intuition, the very possibility of a simple phenomenon is perfectly inconceivable. Reason has no right whatever to assume, as an opinion, purely intelligible beings, or purely intelligible qualities of the objects of the senses; although, on the other side, as we have no concepts whatever, either of their possibility or impossibility, we cannot claim any truer insight enabling us to deny dogmatically their possibility.
In order to explain given phenomena, no other things or reasons can be adduced but those which, according to the already known laws of phenomena, have been put in connection with them. A transcendental hypothesis, adducing a mere idea of reason for the explanation of natural things, would therefore be no explanation at all, because it would really be an attempt at explaining what, according to known empirical principles, we do not understand sufficiently by something which we do not understand at all. Nor would the principle of such an hypothesis serve to help the understanding with regard to its objects, but only to satisfy our reason. Order and design in nature must themselves be explained on natural grounds and according to natural laws; and for this purpose even the wildest hypotheses, if only they are physical, are more tolerable than a hyperphysical one,—that is, the appeal to the Divine Author, who is called in for that very purpose. This would be a principle of ratio ignava, to pass by all causes the objective reality of which, in their possibility at least, may be known by continued experience, in order to rest on a mere idea, which no doubt is very agreeable to our reason. With regard to the absolute totality of the ground of explanation in the series of causes, there can be no difficulty, considering that all mundane objects are nothing but phenomena, in which we can never hope to find absolute completeness in the synthesis of the series of conditions.
It is impossible to allow transcendental hypotheses in the speculative use of reason, or the use of hyperphysical instead of physical explanations; partly, because reason is not in the least advanced in that way, but, on the contrary, cut off from its own proper employment, partly because such a licence would in the end deprive reason of all the fruits that spring from the cultivation of its own proper soil, namely, experience. It is true, no doubt, that whenever the explanation of nature seems difficult to us, we should thus always have a transcendent explanation ready to hand, which relieves us of all investigation; but in that case we are led in the end, not to an understanding, but to a complete incomprehensibility of the principle which, from the very beginning, was so designed that it must contain the concept of something which is the absolutely First.
What is, secondly, required in order to render an hypothesis acceptable, is its adequacy for determining a priori, by means of it, all the consequences that are given. If, for that purpose, we have to call in the aid of supplementary hypotheses, they rouse the suspicion of a mere fiction, because each of them requires for itself the same justification as the fundamental idea, and cannot serve therefore as a sufficient witness. No doubt, if we once admit an absolutely perfect cause, there is no difficulty in accounting for all the order, magnitude, and design which are seen in the world. But if we consider
what seem to us at least deviations and evils in nature, new hypotheses will be required in order to save the first hypothesis from the objections which it has to encounter. In the same manner, whenever the simple independence of the human soul, which has been admitted in order to account for all its phenomena, is called into question on account of the difficulties arising from phenomena similar to the changes of matter (growth and decay), new hypotheses have to be called in, which may seem plausible, but possess no authority, except what they derive from the opinion which was to yield the chief explanation, and which they themselves were called upon to defend.
If the two hypotheses which we have just mentioned as examples of the assertions of reason (the incorporeal unity of the soul, and the existence of a Supreme Being) are to be accepted, not as hypotheses, but as dogmas proved a priori, we have nothing to say to them. Great care, however, should be taken in that case that they should be proved with the apodictic certainty of a demonstration. It would be as absurd to try to make the reality of such ideas plausible only, as to try to make a geometrical proposition plausible. Reason, independent of all experience, knows everything either a priori, and as necessary, or not at all. Its judgment, therefore, is never opinion, but either an abstaining from all judgments, or apodictic certainty. Opinions and guesses as to what belongs to things can be admitted in explanation only of what is really given, or as resulting, according to empirical laws, from something that is really given. They belong, therefore, to the series of the objects of experience only. Outside that field to opine is the same as to play with thoughts, unless we suppose that even a doubtful and uncertain way of judging might lead us perhaps on to the truth.
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