The lectures, published posthumously, became a text-book for students, and reached a nineteenth edition in 1851. Their faults, considered as philosophical treatises, are palpable. They have the wordiness of hasty composition, and the discursive rhetoric intended to catch the attention of an indolent audience. Brown does not see that he is insulting his hearers when he apologises for introducing logic into lectures upon metaphysics, and indemnifies them by quotations from Akenside and the Essay on Man. Brown, however, showed great acuteness and originality. He made deviations, and took pains to mark his deviations, from Reid, though he spoke more guardedly of his own friend, Stewart. Stewart, who had strongly supported Brown's election, was shocked when, on the publication of the lectures, he came to discover that his colleague had been preaching heresy, and wrote with obvious annoyance of Brown's hastiness and dangerous concessions to the enemy.[468] Brown, however, impressed his contemporaries by his ability. Sydney Smith is probably reporting the current judgment of his own circle when he says[469] that in metaphysics Stewart was a 'humbug' compared with Brown. I certainly think that Stewart, whom I should be sorry to call a humbug, shows less vigour and subtlety. Brown, at any rate, impressed both the Mills, and his relation to them is significant.
Brown's essay upon Causation indicates this relation. In this, indeed, there is little, if any, divergence from Stewart, though he attacks Reid with considerable asperity. He urges that Reid, while really agreeing with Hume, affected to answer him under cover of merely verbal distinctions.[470] The main point is simple. Hume had asserted that all events seem to be 'entirely loose and separate,' or, in other words, 'conjoined but never connected.' Yet he points out that, in fact, when we have found two events to be 'conjoined,' we call one cause and the other effect, and assume a 'necessary connection' between them. He then asks, What is the origin of this belief, and what, therefore, is the logical warrant for its validity? Brown entirely accepts Hume's statement of the facts. The real meaning of our statements is evaded by appealing to the conception of 'power.' When the loadstone (in his favourite illustration) attracts the iron, we say it has a 'power' of attracting iron. But to speak thus of a power is simply to describe the same facts in other words. We assert this, and nothing more than this, that when the loadstone comes near the iron, each moves towards the other. 'Power' is a word which only covers a statement of 'invariable antecedence.' Brown traces the various confusions which have obscured the true nature of this belief. He insists especially that we can no more discover power in mental than in physical sequences. The will had been supposed to be the type of causal power; but volition, according to Brown, reveals simply another succession of desires and bodily actions. The hypothesis of 'power' has been really the source of 'illusion.' The tendency to personify leads us to convert metaphor into fact, to invent a subject of this imaginary 'power,' and thus to create a mythology of beings to carry on the processes of nature. In other words, Brown here follows Hume or even anticipates Comte. As J. S. Mill remarks,[471] this erroneous identification of 'power' with 'will' gives the 'psychological rationale of Comte's great historical generalisation'; and, so far, Brown, as a follower of Hume, is clearly on the way to positivism.
The world, then, is a vast aggregate of 'loose' phenomena. A contemplation of things reveals no reason for one order rather than another. You may look at your loadstone as long as you please, but you will find no reason for its attracting iron. You may indeed interpolate a number of minute intervening sequences, and the process often suggests a vague something more than sequence; but this is a mere illusion.[472] Could we, in fact, see all the minute changes in bodies we should actually perceive that cause means nothing but 'the immediate invariable antecedence of an event.'[473] Brown especially argues against the attempts of d'Alembert and Euler to deduce the first laws of motion from the principle of 'sufficient reason.'[474] That, as he argues in detail, is merely begging the question, by introducing the principle of causation under an alias.
What, then, is the principle? We believe, he says,[475] that 'every event must have a cause,' and that circumstances exactly 'similar must have results exactly similar.' This belief, though applicable to all events, does not give us the 'slightest aid' to determining, independently of experience, any particular event. We observe that B follows A, but, for all we can say, it might as well follow any other letter of the alphabet. Yet we are entitled to say in general that it does uniformly follow some particular letter. The metaphor which describes cause and effect as a 'bond' tying A and B together is perfectly appropriate if taken to express the bare fact of sequence;[476] but we fall into error if we fancy there is really any bond whatever beside the events themselves.
The belief, then, in causation has precisely the same import according to Hume and Brown; and both agree that it is not produced by 'reasoning.' The proposition 'B has once succeeded A,' or 'has succeeded A a thousand times,' is entirely different from the proposition 'B will for ever succeed A.'[477] No process of logical inference can extract one from the other. Shall we, then, give up a belief in causation? The belief in any case exists as a fact. Hume explains it by custom or association. Brown argues, and I think with much force, that Hume's explanation is insufficient. Association may explain (if it does more than restate) the fact that one 'idea' calls up another idea, but such association may and often does occur without suggesting any belief. The belief, too, precedes the association. We begin by believing too much, not too little, and assume a necessary connection of many phenomena which we afterwards find to be independent. The true answer is therefore different. There are three sources of belief, 'perception,' 'reasoning,' and 'intuition.'[478] Now, we cannot 'perceive' anything but a present coincidence; neither can we establish a connection by any process of 'reasoning,' and therefore the belief must be an 'intuition.' This, accordingly, is Brown's conclusion. 'There are principles,' he says, 'independent of reasoning, in the mind which save it from the occasional follies of all our ratiocinations';[479] or rather, as he explains, which underlie all reasoning. The difference, then, between Hume and Brown (and, as Brown argues, between Hume and Reid's real doctrine) is not as to the import, but as to the origin, of the belief. It is an 'intuition' simply because it cannot be further analysed. It does not allow us to pass a single step beyond experience; it merely authorises us to interpret experience. We can discover any actual law of connection between phenomena only by observing that they occur in succession. We cannot get beyond or behind the facts—and therefore intuitionism in this sense is not opposed to empiricism, but a warrant for empirical conclusions. An 'intuition,' briefly, is an unanalysable belief. Brown asserts that a certain element of thought has not been explained, and assumes it to be therefore inexplicable or ultimate. Brown's account of causation had a great influence upon both the Mills, and especially affected the teaching of the younger Mill.
Another point is important. Reid, as I have said, had specially prided himself upon his supposed overthrow of Berkeley's idealism. He was considered to have shown, in spite of sceptics, that the common belief in an external world was reasonable. Brown in his lectures ridiculed Reid's claim. This 'mighty achievement,' the 'supposed overthrow of a great system,' was 'nothing more than the proof that certain phrases are metaphorical, which were intended by their authors to be understood only as metaphors.'[480] The theory was dead before Reid slew it, though the phrases were still used as a mere 'relic,' or survival of an obsolete doctrine.[481] The impossibility of constructing extension out of our sensations is the experimentum crucis upon which Reid was ready to stake his case. If the attempt at such a construction could succeed, he would 'lay his hand upon his mouth' and give up the argument.[482] Brown takes up the challenge thus thrown out. He holds that our knowledge of an external world is derived from a source which Reid overlooked. He modifies the Scottish psychology by introducing the muscular senses. His theory is that the infant which has learned to move discovers that on some occasions its movements are modified by a sense of 'impeded effort.'[483] The sudden interruption to a well-known series excites in its mind the notion of 'a cause which is not in itself.' This is the source of our belief in an external world. That belief is essentially the belief in some cause which we know to be other than our own mental constitution or the series of 'internal' phenomena, and of which we can know nothing else. It is enough to indicate a theory which has been elaborated by later psychologists, and plays a great part (for example) in the theories of Mill, Bain, and Mr. Herbert Spencer. It shows the real tendency of Brown's speculations. In the first place, it must be noticed that the theory itself had been already emphatically stated by Destutt de Tracy. Hamilton accuses Brown of plagiarism.[484] Whether his accusation be justifiable or not, it is certainly true that Brown had in some way reached the same principles which had been already set forth by a leading 'ideologist.' Brown, that is, though the official exponent of the Scottish philosophy, was in this philosophical tenet at one with the school which they regarded as materialistic or sceptical. The path by which he reaches his conclusions is also characteristic.
Brown has reversed the interpretation of Reid's experimentum crucis. I will give up my case, says Reid, if you can make the external world out of sensations. That, replies Brown, is precisely what we can do. How from sensations do we get what Berkeley called 'outness'? We get it, says Brown, from the sense of resistance or 'impeded effort.' That reveals to us the fact that there is something independent of ourselves, and the belief in such a something is precisely what we mean, and all that we mean, by the belief in an external world. Consistently with this, Brown rejects Reid's distinction between the primary and secondary qualities. The distinction corresponds no doubt to some real differences, but there is no difference of the kind suggested by Reid. 'All [the qualities] are relative and equally relative—our perception of extension and resistance as much as our perception of fragrance and bitterness.'[485] We ascribe the sensations to 'external objects,' but the objects are only known by the 'medium' of our sensations. In other words, the whole world may be regarded as a set of sensations, whether of sight, smell, touch, or resistance to muscular movement, accompanied by the belief that they are caused by something not ourselves, and of which something we can only say that it is not ourselves.
Once more, the analysis of the process by which the belief is generated is significant. From resistance, or the sensation produced when something 'resists our attempts to grasp it,' we get the 'outness.' Then perception is 'nothing more than the association of this complex notion with our other sensations—the notion of something extended and resisting, suggested by these sensations, when the suggestions themselves have previously arisen, and suggested in the same manner and on the same principle as any other associate feeling suggests any other associate feeling.'[486] The odour or colour of a rose recalls the sensation of touching and of resistance to our grasp. Thus we regard the whole group of sensations as due to the external cause which produces the sensation of resistance. Brown seems to hesitate a little as to whether he shall appeal to an 'intuition' or to 'association,' but 'as I rather think,' he says, the belief is founded 'on associations as powerful as intuition.'[487]
Whatever, then, may be the origin of the belief—'intuition' or 'association'—it is clear that it can give us no knowledge except such as is derived from sensations. Moreover, Brown is thus led, as in the doctrine of causation, to accept a really sceptical position. He declares that he is in this respect at one with both Reid and Hume. They both accept two propositions: first, that we cannot 'by mere reasoning' prove the existence of an external world; secondly, that it is 'absolutely impossible for us not to believe' in its existence. Hume, he says, pronounces the first proposition in a 'loud tone of voice' and 'whispers' the second. Reid, conversely, passes over the first rapidly and 'dwells on the second with a tone of confidence.'[488] Brown accepts both statements. He has already said that there is no argument against Berkeley's denial of matter any more than against the 'infinite divisibility of matter.' But he adds, it is 'physically impossible' for us to admit the conclusion, at least without 'an instant dissent from a momentary logical admission.'[489] This, indeed, is but a version of Hume's familiar statement that Berkeley's arguments admit of no reply and produce no conviction.
Another essential doctrine of the Mills, the 'association' theory, is treated differently by Brown. Brown, as we have seen, both in his theory of causation and in his theory of our belief in an external world, speaks of principles in the mind which somehow override 'ratiocination.' In the first case, he speaks of 'intuition,' but in the other, as I have said, he seems to prefer association. The difference is remarkable because the belief in an external world is upon his showing simply a case of causation. It means essentially the reference of our sensations as to an external cause. Now, in the argument upon causation, he has insisted upon the insufficiency of association to generate the belief; and he would have found it difficult to meet his own arguments if applied to the belief in an external world. Yet it does not seem to occur to him that there is any difficulty in explaining this belief in an external world as a case of what Mill called 'indissoluble association.' Brown, as Mill thought, was not sufficiently aware of the power of this principle, and the difference between them is marked by this divergence. Brown had a great deal to say about association, though he chose generally to substitute the word 'suggestion,' previously familiar to Reid and Berkeley.[490] He considers it, however, mainly in another relation. He proposes to trace the order in which 'trains' of ideas succeed each other in our minds. He does not dwell upon the influence of association in producing belief. His question is not primarily as to the logic, but as to the actual succession of our thoughts. He explains that he uses the word 'suggestion' in order to avoid the hypothesis that the sequence of two ideas necessarily implies a previous state of mind in which they were brought together; and endeavours to explain various cases (as, for example, association by 'contrast' as well as by 'likeness' or 'continuity') by a more 'subtile' analysis.[491] He then works out an elaborate theory of 'simple' and 'relative' suggestion. Simple 'suggestion'[492] corresponds mainly to ordinary association, as when a friend's name or his book calls up the thought of the man himself. 'Relative suggestion' arises when two or more objects are perceived and suggest various relations of likeness and so forth.[493] This provides a scheme for working out the whole doctrine of the sequences of ideas so far as the sequences depend upon the mind itself and not upon external causes. It thus leads to problems of abstraction and generalisation and to his whole theory of what he calls the 'intellectual states.' He again closely coincides with the French ideologists. He starts by examining Locke and Condillac. He of course professes to hold that Condillac's version of Locke is illegitimate, and ridicules the famous formula penser c'est sentir. He is, however, equally unwilling to admit Reid's 'variety of powers.'[494] In fact, his criticism of Condillac shows more affinity than contrast. Condillac erred, he says, in holding that thoughts are 'transformed sensations.' This was a false simplification into which he considers Condillac to have been led partly by the ambiguity of the word sentir.[495] Condillac applied to the mind the theory, true in 'the chemistry of the material chemists,' that the 'compounds are the elements themselves.'[496] He errs when he infers from the analogy that a feeling which arises out of others can be resolved into them. 'Love and hate' and other emotions are fundamentally different from the sensations by which they are occasioned, not mere 'transformations' of those sensations. We, on the other hand (that is to say, Reid and Stewart), have erred by excessive amplification. Instead of identifying different things, we have admitted a superfluous number of 'ultimate principles.'