662 PSYCHOLOGY. 



of the laios of habit in the nervous system; in other ivords, 

 it is to ascribe it to a physiological cause. If it be truly 

 a law of those nerve-centres wliicli co-ordinate sensory 

 and motor processes together that paths once used for 

 coupling any pair of them are thereby made more permea- 

 ble, there appears no reason why the same law should not 

 hold good of ideational centres and their coupling-paths as 

 welL" Parts of these centres which have once been in 

 action together will thus grow so linked that excitement at 

 one point will irradiate through the system. The chances 

 of complete irradiation will be strong in proportion as the 

 previous excitements have been frequent, and as the 

 present points excited afresh are numerous. If all points 

 were originally excited together, the irradiation may be 

 sensibly simultaneous throughout the system, Avheu any 

 single point or group of points is touched off. But where 

 the original impressions were successive — the conjugation of 



* The difficult}^ here as with habit uherhaupt is in seeing how new 

 j'aths come first to be formed (cf . above, 109). Experience shows that a 

 new path is formed between centres for sensible impressions whenever 

 these vibrate together or in rapid succession. A child sees a certain bottle 

 and hears it called ' milk, 'and thenceforward thinks the name when he again 

 sees the bottle. But why the successive or simultaneous excitement of two 

 centres independently stimulated from without, one by sight and the 

 other by hearing, should result in a path between them, one does not im- 

 mediately see. We can only make hypotheses. Any hypothesis of the 

 specific mode of their formation which tallies well with the observed facts 

 of association will be in so far forth credible, in spite of po.ssible obscurity. 

 Herr Miinsterberg thinks (Beitrage zur exp. Psychologie, Heft 1, p. 132) 

 that between centres excited successively from without no path ought to 

 be formed, and that consequently all contiguous association is between 

 dmuUnneous experiences. Mr. Ward {loc. citt) thinks, on the contrary, that 

 it can onl}' be between successive experiences : " The association of objects 

 simultaneousl}^ presented can be resolved into an association of objects 

 successively attended to. . . . It .seems hardly possible to mention a case 

 in which attention to the associated objects could not have been successive. 

 In fact, an aggregate of objects on which attention could be focussed at 

 once viould be already associated." Between these extreme possibilities, 

 I have refrained from deciding in the text, and have described contiguous 

 assDcintlon as holding between both successively and coexistently pre- 

 sented objects. The phy.siological question as to how we may conceive 

 the paths to originate had better be postponed till it comes to us again in 

 the chapter on the Will, where we can treat it in a broader way. It is 

 eno.igh here to have called attention to it as a serious problem. 



