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;13but 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.'14No 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.'15Now,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';16or 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 specify 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.'17The theory was dead before Reid slew it,though the phrases were still used as a mere 'relic,'or survival of an obsolete doctrine.18The 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.19Brown 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.'20The 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.21Whether 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.