A Treatise of Human Nature · David Hume
GENERAL INTRODUCTION TO VOL. I.
The admission that no relations of quantity are data of sense removes difficulty as to general propositions about them. 276. Here, as elsewhere, what we have to lament is not that Hume ‘pushed his doctrine too far,’ so far as to exclude ideas of those exact proportions in space with which geometry purports to deal, but that he did not carry it far enough to see that it excluded all ideas of quantitative relations whatever. He thus pays the penalty for his equivocation between a feeling of colour and a disposition of coloured points. Even alongside of his admission that ‘relations of space and time’ are independent of the nature of the ideas so related, which amounts to the admission that of space and time there are no ideas at all in his sense of the word, he allows himself to treat ‘proportions between spaces’ as depending entirely on our ideas of the spaces--depending on ideas which in the context he by implication admits that we have not.
Hume does virtually admit this in regard to numbers. 277. To have arrived at this conclusion Hume had only to extend to proportions in space the principle upon which the impossibility of sensualizing arithmetic compels him to deal with proportions in number. ‘We are possessed,’ he says, ‘of a precise standard by which we can judge of the equality and proportion of numbers; and according as they correspond or not to that standard we determine their relations without any possibility of error. When two numbers are so combined, as that the one has always an unite answering to every unite of the other, we pronounce them equal’. [1] Now what are the unites here spoken of? If they were those single impressions which he elsewhere [2] seems to regard as alone properly unites, the point of the passage would be gone, for combinations of such unites could at any rate only yield those ‘general appearances’ of whose proportions we have been previously told there can be no precise standard. They can be no other than those unites which, not being impressions, he has to call ‘fictitious denominations’--unites which are nothing except in relation to each other and of which each, being in turn divisible, is itself a true number.
We can easily retort upon Hume, then, when he argues that the supposition of infinite divisibility is incompatible with any comparison of quantities because with any unite of measurement, that, according to his own virtual admission, in the only case where such comparison is exact the ultimate unite of measurement is still itself divisible; which, indeed, is no more than saying that whatever measures quantity must itself be a quantity, and that therefore quantity is infinitely divisible. If Hume, instead of slurring over this characteristic of the science of number, had set himself to explain it, he would have found that the only possible explanation of it was one equally applicable to the science of space--that what is true of the unite, as the abstraction of distinctness, is true also of the abstraction of externality. As the unite, because constituted by relation to other unites, so soon as considered breaks into multiplicity, and only for that reason is a quantity by which other quantities can be measured; so is it also with the limit in whatever form abstracted, whether as point, line, or surface.
If the fact that number can have no least part since each part is itself a number or nothing, so far from being incompatible with the finiteness of number, is the consequence of that finiteness, neither can the like attribute in spaces be incompatible with their being definite magnitudes, that can be compared with and measured by each other. The real difference, which is also the rationale of Hume’s different procedure in the two cases, is that the conception of space is more easily confused than that of number with the feelings to which it is applied, and which through such application become sensible spaces. Hence the liability to the supposition, which is at bottom Hume’s, that the last feeling in the process of diminution before such sensible space disappears (being the ‘minimum visibile’) is the least possible portion of space. [1] P. 374. [Book I, part III., sec. I.] [2] Above, par. 258. With Hume idea of vacuum impossible, but logically not more so than that of space.
278. Just as that reduction of consciousness to feeling, which really excludes the idea of quantity altogether, is by Hume only recognised as incompatible with its infinite divisibility, so it is not recognised as extinguishing space altogether, but only space as a vacuum. If it be true, he says, ‘that the idea of space is nothing but the idea of visible or tangible points distributed in a certain order, it follows that we can form no idea of vacuum, or space where there is nothing visible or tangible’. [1] Here as elsewhere the acceptability of his statement lies in its being taken in a sense which according to his principles cannot properly belong to it. It is one doctrine that the ideas of space and body are essentially correlative, and quite another that the idea of space is equivalent to a feeling of sight or touch. It is of the latter doctrine that Hume’s denial of a vacuum is the corollary; but it is the former that gains acceptance for this denial in the mind of his reader. Space we have already spoken of as the relation of externality.
If, abstracting this relation from the world of which it is the uniform but most elementary determination, we regard it as a relation between objects having no other determination, these become spaces and nothing but spaces--space pure and simple, _vacuum_. But we have known the world in confused fulness before we detach its constituent relations in the clearness of unreal abstraction. We have known bodies συγκεχυμένος [2], before we think their limits apart and out of these construct a world of pure space. It is thus in a sense true that in the development of our consciousness an idea of body precedes that of space, though the _abstraction_ of space--the detachment of the relation so-called from the real complex of relations--precedes that of body; and it is this fact that, in the face of geometry, strengthens common sense in its position that an idea of vacuum is impossible. It is not, however, the inseparability of space from body whether in reality or for our consciousness, but its identity with a certain sort of feeling, that is implied in Hume’s exclusion of the idea of vacuum. ‘Body,’ as other than feeling, is with him as much a fiction as vacuum. That there can be no idea of vacuum, is thus in fact merely his negative way of putting that proposition of which the positive form is, that space is a compound impression of sight and touch. Having examined that proposition in the positive, we need not examine it again in the negative form. It will be more to the purpose to enquire whether the ‘tendency to suppose’ or ‘propensity to feign’ by which, in the absence of any such idea, our language about ‘pure space’ has to be accounted for, does not according to Hume’s own showing presuppose such an idea.
Wherein consists the difference between these two cases? No one will scruple to affirm that it consists merely in the perceiving those objects, and that the sensation which arises from the motion is in both cases the same; and as that sensation is not capable of conveying to us an idea of extension, when unaccompanied with some other perception, it can no more give us that idea, when mixed with the impressions of tangible objects, since that mixture produces no alteration upon it’. [2] But though a ‘distance not filled with any coloured or solid object’ cannot give us an idea of vacuum, it is the cause why we falsely imagine that we can form such an idea. There are ‘three relations’--_natural_ relations according to Hume’s phraseology [3]--between it and that distance which really ‘conveys the idea of extension.’ ‘The distant objects affect the senses in the same manner, whether separated by the one distance or the other; the former species of distance is found capable of receiving the latter; and they both equally diminish the force of every quality. These relations betwixt the two kinds of distance will afford us an easy reason why the one has so often been taken for the other, and why we imagine we have an idea of extension without the idea of any object either of the sight or feeling’. [4]
They may be ‘impressions,’ there may be ‘impressions of them,’ but only if we deny of the impression what Hume asserts of it, and assert of it what he denies--only if we understand by ‘impression’ not an ‘internal and perishing existence;’ not that which, if other than taste, colour, sound, smell or touch, must be a ‘passion or emotion ‘; _not_ that which carries no reference to an object other than itself, and which must _either_ be single _or_ compound; but something permanent and constituted by permanently coexisting parts; something that may ‘be conjoined with’ any feeling, because it is none; that always carries with it a reference to a subject which it is not but of which it is a quality; and that is both many and one, since ‘in its simplicity it contains many different resemblances and relations.’ 282. In the account just adduced of vacuum, the effect of that double dealing with ‘impressions,’ which we shall have to trace at large in Hume’s explanation of our language about Causation and Identity, is already exhibited in little. Just as, after the idea of pure space has been excluded because not a copy of any possible impression, we yet find an ‘idea,’ only differing from it in name, introduced as the basis of that tendency to suppose which is to take the place of the excluded idea, so we shall find ideas of relation in the way of Identity and Causation--ideas which according to Hume we have not--presupposed as the source of those ‘propensities to feign’ which he accounts for the appearance of our having them.
Knowledge of relation in way of Identity and Causation excluded by Locke’s definition of knowledge. 283. The primary characteristic of these relations according to Hume, which they share with those of space and time, and which in fact vitiates that definition of ‘philosophical relation,’ as depending on comparison, which he adopts, is that they ‘depend not on the ideas compared together, but may be changed without any change in the ideas’. [1] It follows that they are not objects of knowledge, according to the definition of knowledge which Hume inherited, as ‘the perception of agreement or disagreement between ideas.’ A partial recognition of this consequence in regard to cause and effect we found in Locke’s suspicion that a science of nature was impossible--impossible because, however often a certain ‘idea of quality and substance’ may have followed or accompanied another, such sequence or accompaniment never amounts to agreement or ‘necessary connexion’ between the ideas, and therefore never can warrant a general assertion, but only the particular one, that the ideas in question have so many times occurred in such an order. ‘Matters of fact,’ however, which no more consist in agreement of ideas than does causation, are by Locke treated without scruple as matter of knowledge when they can be regarded as relations between present sensations.
Thus the ‘particular experiment’ in Physics constitutes knowledge--the knowledge, for instance, that a piece of gold is now dissolved in aqua regia; and when ‘I myself see a man walk on the ice, it is knowledge.’ In such cases it does not occur to him to ask, either what are the ideas that agree or how much of the experiment is a present sensation. [2] Nor does Hume commonly carry his analysis further. After admitting that the relations called ‘identity and situation in time and place’ do not depend on the nature of the ideas related, he proceeds: ‘When both the objects are present to the senses along with the relation, we call _this_ perception rather than reasoning; nor is there in this case any exercise of the thought or any action, properly speaking, but a mere passive admission of the impressions through the organs of sensation. According to this way of thinking, we ought not to receive as reasoning any of the observations we may make concerning _identity_ and the _relations_ of _time_ and _place_; since in none of them the mind can go beyond what is immediately present to the senses, either to discover the real existence or the relations of objects’. [3] [1] P. 372. [Book I, part III., sec. I.] [2] Above, §§ 122 & 123.
Nor, for the assimilation of reasoning to perception, is anything further needed than a reference to the connection of ideas with impressions and of the ideas of imagination with those of memory, as originally stated by Hume. When both of the objects compared are present to the senses, we call the comparison perception; when neither, or only one, is so present, we call it reasoning. But the difference between the object that is present to sense, and that which is not, is merely the difference between impression and idea, which again is merely the difference between the more and the less lively feeling. [2] To feeling, whether with more or with less vivacity, every object, whether of perception or reasoning, must alike be present. Is it then a sufficient account of the matter, according to Hume, to say that when we are conscious of contiguity and succession between objects of which both are impressions we call it perception; but that when both objects are ideas, or one an impression and the other an idea, we call it reasoning? Not quite so. Suppose that I ‘have seen that species of object we call flame, and have afterwards felt that species of sensation we call heat.’ If I afterwards remembered the succession of the feeling upon the sight, both objects (according to Hume’s original usage of terms [3]) would be ideas as distinct from the impressions; or, if upon seeing the flame I remembered the previous experience of heat, one object would be an idea; but we should not reckon it a case of reasoning. ‘In all cases wherein we reason concerning objects, there is only one either perceived or _remembered_, and the other is supplied in conformity to our past experience’--supplied by the only other faculty than memory that can ‘supply an idea,’ viz. imagination. [4]
Account of the inference given by Locke and Clarke rejected. 288. With the first of the above questions Hume only concerns himself so far as to show that we cannot know either intuitively or demonstratively, in Locke’s sense of the words, that ‘everything whose existence has a beginning also has a cause.’ Locke’s own argument for the necessity of causation--that ‘something cannot be produced by nothing’--as well as Clarke’s--that ‘if anything wanted a cause it would produce itself, _i.e._ exist before it existed’--are merely different ways, as Hume shows, of assuming the point in question. ‘If everything must have a cause, it follows that upon exclusion of other causes we must accept of the object itself, or of nothing, as causes. But ’tis the very point in question, whether everything must have a cause or not’. [1] On that point, according to Locke’s own showing, there can be no certainty, intuitive or demonstrative; for between the idea of beginning to exist and the idea of cause there is clearly no agreement, mediate or immediate. They are not similar feelings, they are not quantities that can be measured against each other, and to these alone can the definition of knowledge and reasoning, which Hume retained, apply. There thus disappears that last remnant of ‘knowledge’ in regard to nature which Locke had allowed to survive--the knowledge that there is a necessary connection, though one which we cannot find out. [2]
What we _do_ find is their ‘constant conjunction’ in experience, and ‘conjunction’ is equivalent to that ‘contiguity in time and place,’ which has already been pointed out as one of those ‘natural relations’ which act as ‘principles of union’ between ideas. [3] Because the impression of flame has always been found to be followed by the impression of heat, the idea of flame always suggests the idea of heat. It is simple custom then that determines the transition from the one to the other, or renders ‘necessary’ the connection between them. In order that the transition, however, may constitute an inference from cause to effect (or _vice versâ_), one of the two objects thus naturally related, but not both, must be presented as an impression. If both were impressions it would be a case of ‘sensation, not reasoning;’ if both were ideas, no belief would attend the transition. This brings us to the question as to the ‘nature and qualities’ of the inferred idea. [1] Above, par. 195. [2] Cf. Locke IV. 17, 2. [3] Above, par. 206. _c_. The qualities of this idea.
291. ‘’Tis evident that all reasonings from causes or effects terminate in conclusions concerning matter of fact, _i.e._ concerning the existence of objects or of their qualities’; [1] in other words, in belief. If this meant a new idea, an idea that we have not previously had, it would follow that inference could really carry us beyond sense, that there could be an idea not copied from any prior impression. But according to Hume it does not mean this. ‘The idea of existence is the very same with the idea of what we conceive to be existent;’ [2] and not only so, ‘the _belief_ of existence joins no new ideas to those which compose the idea of the object. When I think of God, when I think of him as existent, and when I believe him to be existent, my idea of him neither increases nor diminishes’. [3] In what then lies the difference between incredulity and belief; between an ‘idea assented to,’ or an object believed to exist, and a fictitious object or idea from which we dissent? The answer is, ‘not in the parts or composition of the idea, but in the manner of conceiving it,’ which must be understood to mean the manner of ‘feeling’ it; and this difference is further explained to lie in ‘the superior force, or vivacity, or steadiness’ with which it is felt.’ [4] We are thus brought to the further question, how it is that this ‘superior vivacity’ belongs to the inferred idea when we ‘reason’ from cause to effect or from effect to cause. The answer here is that the ‘impression of the memory or senses,’ which in virtue of a ‘natural relation’ suggests the idea, also ‘communicates to it a share of its force or vivacity.’
296. Our first enquiry must be how far these definitions are really consistent with the theory from which they are derived. At the outset, it is a surprise to find that the ‘philosophical relation’ of cause and effect, as distinct from the natural one, should still appear to survive. Such a distinction has no meaning unless it implies a conceived relation of objects other than the _de facto_ sequence of feelings, of which one ‘naturally’ introduces the other. It is the characteristic of Locke’s doctrine of knowledge that in it this distinction is still latent. His language constantly implies that knowledge, as a perception of relations, is other than the sequence of feelings; but by confining his view chiefly to relation in the way of likeness and unlikeness--a relation that exists between feelings merely as felt, or as they are for the feeling consciousness--he avoids the necessity of deciding what the ‘ideas’ are in the connection of which knowledge and reasoning consist, whether objects constituted by conceived relations or feelings suggestive of each other. But when once attention had been fixed, as it was by Hume, on an ostensible relation between objects, like that of cause and effect, which, if it exist at all, is clearly not one in the way of resemblance between feelings, the distinction spoken of becomes patent. If the colour red had not the likeness and unlikeness which it has to the colour blue, the colours would be different feelings from what they are; but if the flame of fire and its heat were not regarded severally as cause and effect, it would make no difference to them as feelings; or, to put it conversely, it is not upon any comparison of two feelings with each other that we regard them as related in the way of cause and effect. In what sense then can the relation between flame and heat be a philosophical relation, as defined by Hume--a relation in virtue of which we compare objects, or an idea that we acquire upon comparison?
Examination of Hume’s language about them. 297. This definition, indeed, is not stated so exactly or so uniformly as might be wished. In different passages ‘philosophical relation’ appears as that in respect of which we compare any two ideas; as that of which we acquire the idea by comparing objects, [1] and finally (in the context of the passage last quoted) as itself the comparison. [2] The real source of this ambiguity lies in that impossibility of regarding an object as anything apart from its relations, which compels any theory that does not recognize it to be inconsistent with itself. It is Locke’s cardinal doctrine that real ‘objects’ are first given as simple ideas, and that their relations, unreal in contrast with the simple ideas, are superinduced by the mind--a doctrine which Hume completes by excluding all ideas that are not either copies of simple feelings or compounds of these, and by consequence ideas of relation altogether. The three statements of the nature of philosophical relation, given above, mark three stages of departure from, or approach to, consistency with this doctrine. The first, implying as it does that relation is not merely a subjective result in our minds from the comparison of ideas, but belongs to the ideas themselves, is most obviously inconsistent with it according to the form in which it is presented by Locke; but the second is equally incompatible with Hume’s completion of the doctrine, for it implies that we so compare ideas as to acquire an idea of relation other than the ideas put together--an idea at once open to Hume’s own challenge, ‘Is it a colour, sound, smell, &c.; or is it a passion or emotion?’
The comparison is between present and past experience of succession of objects. 299. The modern followers of Hume may perhaps seek refuge in the consideration that though the relation of cause and effect between objects is not one in the way of resemblance or one of which the idea is given by comparison of the objects, it yet results from comparisons, which may be supposed to act like chemical substances whose combination produces a substance with properties quite different from those of the combined substances, whether taken separately or together. Some anticipation of such a solution, it may be said, we find in Hume himself, who is aware that from the repetition of impressions of sense and their ideas new, heterogeneous, impressions--those of ‘reflection’--are formed. Of this more will be said when we come to Hume’s treatment of cause and effect as a ‘natural relation.’ For the present we have to enquire what exactly is implied in the comparisons from which this heterogeneous idea of relation is derived. If we look closely we shall find that they presuppose a consciousness of relations as little reducible to resemblance, _i.e._ as little the result of comparison, as that of cause and effect itself.
It has been already noticed how Hume treats the judgment of proportion between figures as a mere affair of sense, because such relation depends entirely on the ideas compared, without reflecting that the existence of the figures presupposes those relations of space to which, because (as he admits) they do not depend on the comparison of ideas, the only excuse for reckoning any relation sensible does not apply. In the same way he contents himself with the fact that the judgment of cause and effect implies a comparison of present with past experience, and may thus be brought under his definition of ‘philosophical relation,’ without observing that the experiences compared are themselves by no means reducible to comparison. We judge that an object, which we now find to be precedent and contiguous to another, is its cause when, comparing present experience with past, we find that it always has been so. That in effect is Hume’s account of the relation, ‘considered as a philosophical one:’ and it implies that the constitution of the several experiences compared involves two sorts of relation which Hume admits not to be derived from comparison, _(a)_ relation in time and place, _(b)_ relation in the way of identity. Observation of succession already goes beyond sense.
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