Hume makes conceptions of identity and cause each come before the other. Their true correlativity.
313. Against this derivation of the conception of cause and effect, as implying that of identity, may be urged the fact that when we would ascertain the truth of any identification we do so by reference to causes and effects. As Hume himself puts it at the outset of his discussion of causation, an inference of identity ‘beyond the impressions of our senses can be founded only on the connexion of cause and effect.’ … ‘Whenever we discover a perfect resemblance between a new object and one which was formerly present to the senses, we consider whether it be common in that species of objects; whether possibly or probably any cause could operate in producing the change and resemblance; and according as we determine concerning these causes and effects, we form our judgment concerning the identity of the object’. [1] This admission, it may be said, though it tells against Hume’s own subsequent explanation of identity as a fiction of the imagination, is equally inconsistent with any doctrine that would treat identity as the presupposition of inference to cause or effect. Now undoubtedly if the identity of interrupted perceptions is one fiction of the imagination and the relation of cause and effect another, each resulting from ‘custom,’ to say with Hume, that we must have the idea of cause in order to arrive at the supposition of identity, is logically to exclude any derivation of that idea from an experience which involves the supposition of identity. The ‘custom’ which generates the idea of cause must have done its work before that which generates the supposition of identity can begin. Hume therefore, after the admission just quoted, was not entitled to treat the inference to cause or effect as a habit derived from experience of identical things. But it is otherwise if the conceptions of causation and identity are correlative—not results of experience of which one must be formed before the other, but co-ordinate expressions of one and the same synthetic principle, which renders experience possible. And this is the real state of the case. It is true, as Hume points out, that when we want to know whether a certain sensation, precisely resembling one that we have previously experienced, represents the same object, we do so by asking how otherwise it can be accounted for. If no difference appears in its antecedents or sequents, we identify it—refer it to the same thing—as that previously experienced; for its relations (which, since it is an event in time, take the form of antecedence and sequence) are the thing. The conceptions of identity and of relation in the way of cause and effect are thus as strictly correlative and inseparable as those of the thing and of its relations. Without the conception of identity experience would want a centre, without that of cause and effect it would want a circumference. Without the supposition of objects which ‘existing at one time are the same with themselves as existing at other times’—a supposition which at last, when through acquaintance with the endlessness of orderly change we have learnt that there is but one object for which such identity can be claimed without qualification, becomes the conception of nature as a uniform whole—there could be no such comparison of the relations in which an object is now presented with those in which it has been before presented, as determines us to reckon it the cause or effect of another; but it is equally true that it is only by such comparison of relations that the identity of any particular object can be ascertained.
[1] P. 376. [Book I, part III., sec. II.]
Hume quite right in saying that we do not go more beyond sense in reasoning than in perception.
314. Thus, though we may concede to Hume that neither in the inference to the relation of cause and effect nor in the conclusions we draw from it do we go ‘beyond experience,’ [1] this will merely be, if his account of it as a ‘philosophical relation’ be true, because in experience we already go beyond sense. ‘There is nothing,’ says Hume, ‘in any object considered in itself that can afford us a reason for drawing a conclusion beyond it’ [2]—a statement which to him means that, if the mind really passes from it to another, this is only because as a matter of fact another feeling follows on the first. But, in truth, if each feeling were merely ‘considered in itself,’ the fact that one follows on another would be no fact for the subject of the feelings, no starting-point of intelligent experience at all; for the fact is the relation between the feelings—a relation which only exists for a subject that considers neither feeling ‘in itself,’ as a ‘separate and perishing existence,’ but finds a reality in the determination of each by the other which, as it is not either or both of them, so survives, while they pass, as a permanent factor of experience. Thus in order that any definite ‘object’ of experience may exist for us, our feelings must have ceased to be what according to Hume they are in themselves. They cease to be so in virtue of the presence to them of the Ego, in common relation to which they become related to each other as mutually qualified members of a permanent system—a system which at first for the individual consciousness exists only as a forecast or in outline, and is gradually realized and filled up with the accession of experience. It is quite true that nothing more than the reference to such a system, already necessary to constitute the simplest object of experience, is involved in that interpretation of every event as a changed appearance of an unchanging order, and therefore to be accounted for, which we call inference to a cause or the inference of necessary connection; or, again, in the identification of the event, the determination of its particular nature by the discovery of its particular cause.
[1] Above, pars. 285 & 286.
[2] P. 436 and elsewhere. [Book I, part III., sec. XII.]
How his doctrine might have been developed. Its actual outcome.
315. The supposed difference then between immediate and mediate cognition is no absolute difference. It is not a difference between experience and a process that goes beyond experience, or between an experience unregulated by a conception of a permanent system and one that is so regulated. It lies merely in the degree of fullness and articulation which that conception has attained. If this had been what Hume meant to convey in his assimilation of inference to perception, he would have gone far to anticipate the result of the enquiry which Kant started. And this is what he might have come to mean if, instead of playing fast and loose with ‘impression’ and ‘object,’ using each as plausibility required on the principle of accommodation to the ‘vulgar,’ he had faced the consequence of his own implicit admission, that every perception of an object as identical is a ‘fiction’ in which we go beyond present feeling. As it is, his ‘scepticism with regard to the senses’ goes far enough to empty their ‘reports’ of the content which the ‘vulgar’ ascribe to them, and thus to put a breach between sense and the processes of knowledge, but not far enough to replace the ‘sensible thing’ by a function of reason. In default of such replacement, there was no way of filling the breach but to bring back the vulgar theory under the cover of habits and ‘tendencies to feign,’ which all suppose a ready-made knowledge of the sensible thing as their starting-point. Hence the constant contradiction, which it is our thankless task to trace, between his solution of the real world into a succession of feelings and the devices by which he sought to make room in his system for the actual procedure of the physical sciences. Conspicuous among these is his allowance of that view of relation in the way of cause and effect as an objective reality, which is represented by his definition of it as a ‘philosophical relation.’ It is in the sense represented by that definition that his doctrine has been understood and retained by subsequent formulators of inductive logic; but on examining it in the light of his own statements we have found that the relation, as thus defined, is not that which his theory required, and as which to represent it is the whole motive of his disquisition on the subject. It is not a sequence of impression upon impression, distinguished merely by its constancy; nor a sequence of idea upon impression, distinguished merely by that transfer of liveliness to the idea which arises from the constancy of its sequence upon the impression. It is a relation between ‘objects’ of which each is what it is only as ‘an instance of a species’ that exists continuously, and therefore in distinction from our ‘perishing impressions,’ according to a regular order of ‘contiguity and succession.’ As such existence and order are by Hume’s own showing no possible impressions, and by consequence no possible ideas, so neither are the ‘objects’ which derive their whole character from them.
No philosophical relation admissible with Hume that is not derived from a natural one.