690 PSYCHOLOGY. 



possibly have been connected, trusting that when the righ^j 

 member of the class has turned up it Avill help the thought's 

 revival. Thus we may run through all the places in which 

 we may have had it. AVe may run through the persons 

 Avhom we remember to have conversed Avith, or we may call 

 up successively all the hooks we have lately been reading. 

 If we are trying to remember a person we may run through 

 a list of streets or of professions. Some item out of the 

 lists thus methodically gone over wdll very likely be asso- 

 ciated with the fact we are in need of, and may suggest it 

 or help to do so. And yet the item might never have arisen 

 without such systematic procedure. In scientific research 

 this accumulation of associates has been methodized by 

 Mill under the title of ' The Four Methods of Experi- 

 mental Inquiry.' By the ' method of agreement,' by that 

 of ' difterence,' by those of ' residues ' and ' concomitant 

 variations ' (which cannot here be more nearly defined), we 

 make certain lists of cases ; and by ruminating these lists 

 in our minds the cause we seek will be more likely to 

 emerge. But the final stroke of discovery is only prepared, 

 not effected, by them. The brain-tracts must, of their own 

 accord, shoot the right way at last, or we shall still grope 

 in darkness. That in some brains the tracts do shoot the 

 right way much oftener than in others, and that we cannot 

 tell why, — these are ultimate facts to which we must never 

 close our eyes. Even in forming our lists of instances 

 according to Mill's methods, we are at the mercy of the 

 spontaneous workings of Similarity in our brain. How 

 are a number of facts, resembling the one whose cause we 

 seek, to be brought together in a list unless the one will 

 rapidly suggest the other through association by similarity ? 



SIMILARITY NO ELEMENTARY LAW. 



Such is the analysis I propose, first of the three main 

 types of spontaneous association, and then of voluntary 

 association. It will be observed that the object called up 

 may bear any logical relation ivhatever to the one which sug- 

 gested it. The law requires only that one condition should 

 be fulfilled. The fading object must be due to a brain- 

 process some of whose elements awaken through habit 



