The question, how the singular proposition is possible, the vital one.
224. A great advance in simplification has been made when the false sort of ‘conceptualism’ has thus been got rid of—that conceptualism which opposes knowing and being under the notion that things, though merely individual in reality, may be known as general. This riddance having been achieved, as it was by Hume, the import of the proposition becomes the central question of philosophy, the answer to which must determine our theory of real existence just as much as of the mind. The issue may be taken on the proposition in its singular no less than in its general form. The weakness of Hume’s opponents, indeed, has lain primarily in their allowing that his doctrine would account for any significant predication whatever, as distinct from exclamations prompted by feelings as they occur. This has been the inch, which once yielded, the full ell of his nominalism has been easily won; just as Locke’s empiricism becomes invincible as soon as it is admitted that qualified things are ‘found in nature’ without any constitutive action of the mind. As the only effective way of dealing with Locke is to ask,—After abstraction of all that he himself admitted to be the creation of thought, what remains to be merely found?—so Hume must be met in limine by the question whether, apart from such ideas of relation as according to his own showing are not simple impressions, so much as the singular proposition is possible. If not, then the singularity of such proposition does not consist in any singleness of presentation to sense; it is not the ‘particularity in time’ of a present feeling; and the exclusion of generality, whether in thoughts or in things, as following from the supposed necessity of such singleness or particularity, is quite groundless.
Not relations of resemblance only, but those of quantity also, treated by Hume as feelings.
225. Hitherto the idea of relation which we have had specially in view has been that of relation in the way of resemblance, and the propositions have been such as represent the most obvious ‘facts of observation’—facts about this or that ‘body,’ man or horse or ball. We have seen that these already suppose the thought of an object qualified, not transitory as are feelings, but one to which feelings are referred on their occurrence as resemblances or differences between it and other objects; but that by an equivocation, which unexamined phraseology covers, between the thought of such an object and feeling proper—as if because we talk of seeing a man, therefore a man were a feeling of colour—Hume is able to represent them as mere data of sense, and thus to ignore the difference between related feelings and ideas of relation. Thus the first step has been taken towards transferring to the sensitive subject, as merely sensitive, the power of thought and significant speech. The next is to transfer to it ideas of those other relations [1] which Hume classifies as ‘relations of time and place, proportion in quantity or number, degrees in any quality’. [2] This done, it is sufficiently equipped for achieving its deliverance from metaphysics. An animal, capable of experiments concerning matter of fact, and of reasoning concerning quantity and number, would certainly have some excuse for throwing into the fire all books which sought to make it ashamed of its animality. [3]
[1] The course which our examination of Hume should take was marked out, it will be remembered, by his enumeration of the ‘natural’ relations that regulate the association of ideas. It might seem a departure from this course to proceed, as in the text, from the relation of resemblance to ‘relations of time and place, proportion in quantity or number, and degrees of any quality,’ since these appear in Hume’s enumeration, not of ‘natural’ but of ‘philosophical’ relations. Such departure, however, is the consequence of Hume’s own procedure. Whether he considered these relations merely equivalent to the ‘natural ones’ of resemblance and contiguity, he does not expressly say; but his reduction of the principles of mathematics to data of sense implies that he did so. The treatment of degrees in quality and proportions in quantity as sensible implies that the difference between resemblance and measured resemblance, between contiguity and measured contiguity, is ignored.
[2] p. 368 [Book I, part II., sec. V.]
[3] If we take in our hand any volume of divinity or school-metaphysics, for instance, let us ask, Does it contain any abstract reasoning for quantity or number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Commit it then to the flames, for it can contain nothing but sophistry and illusion.’—‘Inquiry concerning the Human Understanding,’ at the end.
He draws the line between certainty and probability at the same point as Locke; but is more definite as to probability,
226. In thus leaving mathematics and a limited sort of experimental physics (limited by the exclusion of all general inference from the experiment) out of the reach of his scepticism, and in making them his basis of attack upon what he conceived to be the more pretentious claims of knowledge, Hume was again following the course marked out for him by Locke. It will be remembered that Locke, even when his ‘suspicion’ of knowledge is at its strongest, still finds solid ground (a) in ‘particular experiments’ upon nature, expressed in singular propositions as opposed to assertions of universal or necessary connexion, and (b) in mathematical truths which are at once general, certain, and instructive, because ‘barely ideal.’ All speculative propositions that do not fall under one or other of these heads are either ‘trifling’ or merely ‘probable.’ Hume draws the line between certainty and probability at the same point, nor in regard to the ground of certainty as to ‘matter of fact or existence’ is there any essential difference between him and his master. As this ground is the ‘actual present sensation’ with the one, so it is the ‘impression’ with the other; and it is only when the proposition becomes universal or asserts a necessary connection, that the certainty, thus given, is by either supposed to fail. It is true that with Locke this authority of the sensation is a derived authority, depending on its reference to a ‘body now operating upon us,’ while with Hume, so far as he is faithful to his profession of discarding such reference, it is original. But with each alike the fundamental notion is that a feeling must be ‘true while it lasts,’ and that in regard to real existence or matter of fact no other truth can be known but this. Neither perceives that a truth thus restricted is no truth at all—nothing that can be stated even in a singular proposition; that the ‘particularity in time,’ on which is supposed to depend the real certainty of the simple feeling, is just that which deprives it of significance [1]—because neither is really faithful to the restriction. Each allows himself to substitute for the momentary feeling an object qualified by relations, which are the exact opposite of momentary feelings. ‘If I myself see a man walk on the ice,’ says Locke (IV, xv. 5), ‘it is past probability, it is knowledge:’ nor would Hume, though ready enough on occasion to point out that what is seen must be a colour, have any scruple in assuming that such a complex judgment as the above so-called ‘sight’ has the certainty of a simple impression. It is only in bringing to bear upon the characteristic admission of Locke’s Fourth Book, that no general knowledge of nature can be more than probable, a more definite notion of what probability is, and in exhibiting the latent inconsistency of this admission with Locke’s own doctrine of ideas as effects of a causative substance, that he modifies the theory of physical certainty which he inherited. In their treatment of mathematical truths on the other hand, of propositions involving relations of distance, quantity and degree, a fundamental discrepancy appears between the two writers. The ground of certainty, which Hume admits in regard to propositions of this order, must be examined before we can appreciate his theory of probability as it affects the relations of cause and substance.
[1] See above, paragraphs 45 and 97.