It was James Mill's real merit,according to his son,that he carried the principle of association of ideas further than it had been carried by Hartley or other predecessors.51The importance of the doctrine,indeed,is implied in the very statement of the problem.If it be true,or so far as it is true,that our consciousness reveals to us simply a series of 'sensations'and 'ideas,'the question must be how they are combined.'thought succeeds thought,idea follows idea incessantly,'52says Mill;and this phrase assumes 'thoughts and ideas'to be separable atoms.How,then,do they come to coalesce into an apparently continuous stream?The mind is a stream of 'ideas.'If the stream is composed of drops,we must,of course,consider the drops as composing the stream.The question is,What laws can we assign which will determine the process of composition?
the phrase 'association'admittedly expresses some general and very familiar truths.Innumerable connections may be established when there is no assignable ground of connection in the ideas themselves other than the fact of a previous contact.One idea not only calls up the other,but in some way generates a belief in an independent connection.We hear thunder,for example,and think of lightning.The two ideas are entirely distinct and separate,for they are due to different senses.Yet we not only think of lightning when we hear thunder,but we have no doubt that there is a causal connection.
We believe in this connection,again,though no further explanation can be given of the fact.Thunder and lightning have occurred together,and we infer that they will,and even must,occur together.When we examine our whole structure of belief,we find such 'arbitrary'associations pervade it in every direction.Language itself is learned simply by association.
There is no connection whatever between the sound of the word 'man'and the 'ideas'which the word excites,beyond the fact that the sound has been previously heard when the ideas were excited.Here,then,is a phenomenon to be explained or generalised.We have in countless cases a certain connection established for which no further reason can be assigned than the fact of its previous occurrence.On such a ground,we believe that fire burns,that bread is wholesome,that stones fall;and but for such beliefs could know nothing of the outside world.'Contingent'truth,therefore,or truth derived from mere contact.pervades,if it does not constitute,the whole fabric of our whole knowledge.To prove that all our knowledge is derived from experience is,according to Mill,to prove that in some sense or other association of ideas lies at the base of all intellectual processes.When Locke introduced a chapter upon 'Association of Ideas'into the fourth edition of his essay,he treated it as the exceptional case.Some ideas had a connection traceable by reason;others were only connected by 'chance and custom.'Association does not explain reasoning,only the deviations from reasoning.But with Hume and Hartley the relation is inverted.The principle,instead of being an exceptional case,is simply the universal rule from which logical connection may be deduced as a special case.
The facts upon which Mill relied,and the account of them which he gave,require notice and embodiment in any round psychology.In some shape or other they form the starting-point of all later systems.Mill's vigorous application of his principle,worked out with imperfect appreciation and with many oversights,had therefrom,at least,the merit of preparing the ground for a more scientific method.
In any case,however,his conclusions,so far as sound,must be placed in a different framework of theory.It becomes necessary to dwell chiefly upon the curious defects of his theory,if taken as he wished it to be taken,for an ultimate scientific statement.The fact that there is a synthesis and an analysis is expressed by 'association.'But what more can we say?
What are the 'laws'of association?Unless some rule can be given,we shall get nothing that can be called a theory.One idea is not suggested by the other through any logical process.They are still 'conjoined'but not 'connected.'
The connection,therefore,must be given by something different from the ideas themselves.Now the order of the original 'sensations'depends upon the 'objects of nature,'and is therefore left to 'physical philosophy.'53They occur,however,either in 'synchronous'or in 'successive'order.
Then 'ideas'spring up in the order of 'sensations,'and this is the 'general law of association of ideas.'54The synchronous sensations produce synchronous ideas and the successive sensations successive ideas.Finally,the strength of the association between the ideas depends upon 'the vividness of the associated feelings,and the frequency of the association.'55Hume had said that association depended upon three principles,'contiguity in time and place,''causation,'and 'resemblance.'Contiguity in time corresponds to the successive,and contiguity in place to the synchronous,order.Causation,as Brown had finally proved,56means simply antecedence and consequence.'Resemblance'remains and is,as Mill afterwards says,57a most important principle;but in an unlucky moment he is half inclined to reduce even 'resemblance'to 'contiguity.'58Resemblance is,he even suggests,merely 'a case of frequency,'because we generally see like things together.When we see one tree or sheep,we generally see several trees or sheep.J.S.Mill mildly remarks upon this quaint suggestion as the 'least successful simplification'in the book.