A Commentary to Kant's 'Critique of Pure Reason'

by Norman Kemp Smith

Reason is “nothing but a wonderful and unintelligible instinct in our souls.”[1777] It justifies itself by its practical uses, but can afford no standard to which objective reality must conform.

It is from this point of view that Hume states his answer to the problem of perception. Our natural belief in the permanence and identity of objects, as expressed through the principle of substance and attribute, leads us to interpret the objects of sense-perception as independent realities. We interpret our subjective sensations as being qualities of independent substances. Our other natural belief, in the dynamical interdependence of events, as expressed through the principle of causality, leads, however, to the opposite conclusion, that the known objects are merely mental. For by it we are constrained to interpret sensations, not as objective qualities, but only as subjective effects, expressive of the reactions of our psycho-physical organism. The Cartesian problems owe their origin to the mistaken attempt to harmonise, in a theoretical fashion, these two conflicting principles. The conflict is inevitable and the antinomy is insoluble, so long as the two principles are regarded as objectively valid. The only satisfactory solution comes through recognition that reason is unable to account, save in reference to practical ends, even for its own inevitable demands. The principle of substance and attribute and the principle of causality co-operate in rendering possible such organisation of our sense-experience as is required for practical life. But when we carry this organisation further than practical life itself demands, the two principles at once conflict.

Kant shows no interest in this constructive part of Hume’s philosophy; and must, indeed, have been almost entirely ignorant of it, since it finds only very imperfect expression in the Enquiry, and is ignored in Beattie’s Nature of Truth. Accordingly, Kant does not regard Hume as offering a positive explanation of knowledge, but rather as representing the point of view of thoroughgoing scepticism. But even had he been acquainted at first hand with Hume’s Treatise, he would undoubtedly have felt little sympathy with Hume’s naturalistic view of the function of reason. His training in the mathematical sciences would have enabled him to detect the inadequacy of Hume’s treatment of mathematical knowledge, and his strong moral convictions would have led him to rebel against the naturalistic assumptions which underlie Hume’s entire position. The Berkeley-Hume comedy is thus repeated with reversed rôles. Just as Berkeley’s anti-materialistic philosophy was mainly influential as a step towards the naturalism of Hume, and as such still survives in the philosophies of John Stuart Mill, Herbert Spencer, Huxley, Mach and Karl Pearson, so in turn Hume’s anti-metaphysical theory of knowledge was destined to be one of the chief contributory sources of the German speculative movement.

We may now turn to Hume’s treatment of the narrower problem—that of justifying our particular causal judgments. Hume’s attitude towards this question is predetermined by the more fundamental argument, above stated, which precedes it in the Treatise, but which is entirely omitted from the corresponding chapters of the Enquiry. As the general principle of causality is of an irrational character, the same must be true of those particular judgments which are based upon it. Much of Hume’s argument on this question is, indeed, merely a restatement of what had already been pointed out by his predecessors. There is no necessary connection discoverable between any cause and its effect. This is especially evident as regards the connection between brain states and mental experiences. No explanation can be given why a motion in the brain should produce sensations in the mind, or why a mental resolution should produce movements in the body. Such sequences may be empirically verified; they cannot be rationally understood. That this likewise holds, though in less obvious fashion, of the causal interrelations of material bodies, had been emphasised by Geulincx, Malebranche, Locke, and Berkeley. The fact that one billiard ball should communicate motion to another by impact is, when examined, found to be no less incomprehensible than the interaction of mind and body. Hume, in the following passage, is only reinforcing this admitted fact, in terms of his own philosophy.

“We fancy that were we brought on a sudden into this world we could at first have inferred that one billiard ball would communicate motion to another upon impulse; and that we needed not to have waited for the event, in order to pronounce with certainty upon it. Such is the influence of custom, that, where it is strongest, it not only covers our natural ignorance, but even conceals itself, and seems not to take place merely because it is found in the highest degree.”[1778]

Nor are we conscious of any causal power within the self. When Berkeley claims that mind has the faculty of producing images at will, he is really ascribing to it creative agency. And such creation, as Malebranche had already pointed out, is not even conceivable.

“I deny that my will produces in me my ideas, for I cannot even conceive how it could produce them, since my will, not being able to act or will without knowledge, presupposes my ideas and does not make them.”[1779] “Is there not here,” Hume asks, “either in a spiritual or material substance, or both, some secret mechanism or structure of parts, upon which the effect depends, and which, being entirely unknown to us, renders the power or energy of the will equally unknown and incomprehensible?”[1780]

But the fact that Hume thus restates conclusions already emphasised by his predecessors will not justify us in contending (as certain historians of philosophy seem inclined to do) that in his treatment of the causal problem he failed to make any important advance upon the teaching of the Occasionalists. Hume was the first to perceive the essential falsity of the Cartesian, rationalistic view of the causal nexus. For Descartes, an effect is that which can be deduced with logical necessity from the concept of its cause. The Occasionalists similarly argued that because natural events can never be deduced from one another they must in all cases be due to supernatural agency; like Descartes, they one and all failed to comprehend that since by an effect we mean that which follows in time upon its cause, and since, therefore, the principle of causality is the law of change, the nature of causality cannot be expressed in logical terms. Hume was the first to appreciate the significance of this fundamental fact; and an entirely new set of problems at once came into view. If causal connection is not, as previous thinkers had believed, logical in character, if it does not signify logical dependence of the so-called effect upon its cause, its true connotation must lie elsewhere; and until this has been traced to its hidden source, any attempted solution of metaphysical problems is certain to involve many false assumptions. The answer that is given to the problem of the origin and content of the causal concept must determine our interpretation alike of sense-experience and of pure thought.

The problem presents on examination, however, a most paradoxical aspect. As Hume has already shown, every effect is an event distinct from its cause, and there is never any connection, beyond that of mere sequence, discoverable between them. We observe only sequence; we assert necessary connection. What, then, is in our minds when this latter assertion is made? And how, if the notion of necessitated connection cannot be gained through observation of the external events, is it acquired by us? Hume again propounds a naturalistic solution. Causation, i.e. necessitated sequence in time, is not in any sense a conception; it is not a comprehended relation between events, but a misunderstood feeling in our minds. We cannot form any, even the most remote, conception of how one event can produce another. Neither imagination nor pure thought, however freely they may act, are capable of inventing any such notion. But nature, by the manner in which it has constituted our minds, deludes us into the belief that we are in actual possession of this idea. The repeated sequence of events, in fixed order, generates in us the feeling of a tendency to pass from the perception or idea of the one to the idea of the other. This feeling, thus generated by custom, and often in somewhat confused fashion combined with the feeling of ‘animal nisus,’ which is experienced in bodily effort, is mistaken by the mind for a definite concept of force, causality, necessary connection. As mere feeling it can afford no insight into the relation holding between events, and as merely subjective can justify no inference in regard to that relation. The terms force, causality, necessitated sequence in time, have a practical value, as names for our instinctive, natural expectations; but when employed as instruments for the theoretical interpretation of experience, they lead us off on a false trail.

This is one of the fundamental points upon which Hume reveals a deeper speculative insight than either Malebranche, Geulincx, or Locke. Though these latter insist upon our ignorance of the relation holding between events, they still assume that causation and natural necessity are concepts which have a quite intelligible meaning; and in consequence they fail to draw the all-important conclusion, that the general principle of causality has neither intuitive nor demonstrative validity. For that is the revolutionary outcome of Hume’s analysis of the notion of necessitated connection. The principle of causality is a synthetic judgment in which no connection is discoverable between its subject and its predicate. That is the reason why it is neither self-evident nor capable of being established upon more ultimate grounds.