A Treatise of Human Nature / Being an Attempt to Introduce the Experimental Method Into Moral Subjects; and Dialogues Concerning Natural Religion

by David Hume

319. The fallacy of Hume’s doctrine of causation is merely an aggravated form of that which has generally passed muster in his doctrine of time. If time, because a relation between feelings, can be supposed to survive the exclusion of a thinking self and the reduction of the world and mind to a succession of feelings, the relation of cause and effect has only to be assimilated to that of time in order that its incompatibility with the desired reduction may disappear, The great obstacle to such assimilation lies in that opposition to the mere sequence of feelings which causation as ‘matter of fact’—as that in discovering which we ‘discover the real existence and relations of objects’—purports to carry with it. Why do we set aside our usual experience as delusive in contrast with the exceptional experience of the laboratory—why do we decide that an event which has seemed to happen cannot really have happened, because under the given conditions no adequate cause of it could have been operative—if the relation of cause and effect is itself merely a succession of seemings, repeated so often as to leave behind it a lively expectation of its recurrence? This question, once fairly put, cannot be answered: it can only be evaded. It is Hume’s method of evasion that we have now more particularly to notice.

Still, he is a long way off the Inductive Logic, which supposes an objective sequence.

320. In its detailed statement it is very different from the method adopted in those modern treatises of Logic which, beginning with the doctrine that facts are merely feelings in the constitution of which thought has no share, still contrive to make free use in their logical canon of the antithesis between the real and apparent. The key to this modern method is to be found in its ambiguous use of the term ‘phenomenon,’ alike for the feeling as it is felt, ‘perishing’ when it ceases to be felt, and for the feeling as it is for a thinking subject—a qualifying and qualified element in a permanent world. Only if facts were ‘phenomena’ in the former sense would the antithesis between facts and conceptions be valid; only if ‘phenomena’ are understood in the latter sense can causation be said to be a law of phenomena. So strong, however, is the charm which this ambiguous term has exercised, that to the ordinary modern logician the question above put may probably seem unmeaning. ‘The appearance,’ he will say, ‘which we set aside as delusive does not consist in any of the reports of the senses—these are always true—but in some false supposition in regard to them due to an insufficient analysis of experience, in some reference of an actual sensation to a group of supposed possibilities of sensation, called a “thing,” which are either unreal or with which it is not really connected. The correction of the false appearance by a discovery of causation is the replacement of a false supposition, as to the possibility of the antecedence or sequence of one feeling to another, by the discovery, through analysis of experience, of what feelings do actually precede and follow each other. It implies no transition from feelings to things, but only from a supposed sequence of feelings to the actual one. Science in its farthest range leaves us among appearances still. It only teaches us what really appears.’

Can the principle of uniformity of nature be derived from sequence of feelings?

321. Now the presupposition of this answer is the existence of just that necessary connexion as between appearances, just that objective order, for which, because it is not a possible ‘impression or idea,’ Hume has to substitute a blind propensity produced by habit. Those who make it, indeed, would repel the imputation of believing in any ‘necessary connexion,’ which to them represents that ‘mysterious tie’ in which they vaguely suppose ‘metaphysicians’ to believe. They would say that necessary connexion is no more than uniformity of sequence. But sequence of what? Not of feelings as the individual feels them, for then there would be no perfect uniformities, but only various degrees of approximation to uniformity, and the measure of approximation in each case would be the amount of the individual’s experience in that particular direction. The procedure of the inductive logician shows that his belief in the uniformity of a sequence is irrespective of the number of instances in which it has been experienced. A single instance in which one feeling is felt after another, if it satisfy the requirements of the ‘method of difference,’ i.e. if it show exactly what it is that precedes and what it is that follows in that instance, suffices to establish a uniformity of sequence, on the principle that what is fact once is fact always. Now a uniformity that can be thus established is in the proper sense necessary. Its existence is not contingent on its being felt by anyone or everyone. It does not come into being with the experiment that shows it. It is felt because it is real, not real because it is felt. It may be objected indeed that the principle of the ‘uniformity of nature,’ the principle that what is fact once is fact always, itself gradually results from the observation of facts which are feelings, and that thus the principle which enables us to dispense with the repetition of a sensible experience is itself due to such repetition. The answer is, that feelings which are conceived as facts are already conceived as constituents of a nature. The same presence of the thinking subject to, and distinction of itself from, the feelings, which renders them knowable facts, renders them members of a world which is one throughout its changes. In other words, the presence of facts from which the uniformity of nature, as an abstract rule, is to be inferred, is already the consciousness of that uniformity in concreto.

With Hume the only uniformity is in expectation, as determined by habit; but strength of such expectation must vary indefinitely.

322. Hume himself makes a much more thorough attempt to avoid that pre-determination of feelings by the conception of a world, of things and relations, which is implied in the view of them as permanent facts. He will not, if he can help it, so openly depart from the original doctrine that thought is merely weaker sense. Such conceptions as those of the uniformity of nature and of reality, being no possible ‘impressions or ideas,’ he only professes to admit in a character wholly different from that in which they actually govern inductive philosophy. Just as by reality he understands not something to which liveliness of feeling may be an index, but simply that liveliness itself, and by an inferred or believed reality a feeling to which this liveliness has been communicated from one that already has it; so he is careful to tell us ‘that the supposition that the future resembles the past is derived entirely from habit, by which we are determined to expect for the future the same train of objects to which we have been accustomed’. [1] The supposition then is this ‘determination,’ this ‘propensity,’ to expect. Any ‘idea’ derived from the propensity can only be the propensity itself at a fainter stage; and between such a propensity and the conception of ‘nature,’ whether as uniform or otherwise, there is a difference which only the most hasty reader can be liable to ignore. But if by any confusion an expectation of future feelings, determined by the remembrance of past feelings, could be made equivalent to any conception of nature, it would not be of nature as uniform. As is the ‘habit’ which determines the expectation, such must be the expectation itself; and as have been the sequences of feeling in each man’s past, such must be the habit which results from them. Now no one’s feelings have always occurred to him in the same relative order. There may be some pairs of feelings of which one has always been felt before the other and never after it, and between which there has never been an intervention of a third—although (to take Hume’s favourite instance) even the feeling of heat may sometimes precede the sight of the flame—and in these cases upon occurrence of one there will be nothing to qualify the expectation of the other. But just so far as there are exceptions in our past experience to the immediate sequence of one feeling upon another, must there be a qualification of our expectation of the future, if it be undetermined by extraneous conceptions, with reference to those particular feelings.

[1] P. 431. [Book I, part III., sec. XII.]

It could not serve the same purpose as the conception of uniformity of nature.

323. Thus the expectation that ‘the future will resemble the past,’ if the past means to each man (and Hume could not allow of its meaning more) merely the succession of his own feelings, must be made up of a multitude of different expectations—some few of these being of that absolute and unqualified sort which alone, it would seem, can regulate the transition that we are pleased to call ‘necessary connexion;’ the rest as various in their strength and liveliness as there are possible differences between cases where the chances are evenly balanced and where they are all on one side. From Hume’s point of view, as he himself says, ‘every past experiment,’ i.e. every instance in which feeling (a) has been found to follow feeling (b), ‘may be considered a kind of chance’. [1] As are the instances of this kind to the instances in which some other feeling has followed (b), such are the chances or ‘probability’ that (a) will follow (b) again, and such upon the occurrence of (b) will be that liveliness in the expectation of (a), which alone with Hume is the reality of the connexion between them. In such an expectation, in an expectation made up of such expectations, there would be nothing to serve the purpose which the conception of the uniformity of nature actually serves in inductive science. It could never make us believe that a feeling felt before another—as when the motion of a bell is seen before the sound of it has been heard—represents the real antecedent. It could never set us upon that analysis of our experience by which we seek to get beyond sequences that are merely usual, and admit of indefinite exceptions, to such as are invariable; upon that ‘interrogation of nature’ by which, on the faith that there is a uniformity if only we could find it out, we wrest from her that confession of a law which she does not spontaneously offer. The fact that some sequences of feeling have been so uniform as to result in unqualified expectations (if it be so) could of itself afford no motive for trying to compass other expectations of a like character which do not naturally present themselves. Nor could there be anything in the appearance of an exception to a sequence, hitherto found uniform, to lead us to change our previous expectation for one which shall not be liable to such modification. The previous expectation would be so far weakened, but there is nothing in the mere weakening of our expectations that should lead to the effort to place them beyond the possibility of being weakened. Much less could the bundle of expectations come to conceive themselves as one system so as that, through the interpretation of each exception to a supposed uniformity of sequence as an instance of a real one, the changes of the parts should prove the unchangeableness of the whole.