610 PSYCHOLOGY. 



tlie linen of its multitudinous inmates, after it came from 

 tlie wash, by lier wonderfully educated sense of smell. 



The fact is so familiar that few, if any, psychologists have 

 even recognized it as needing explanation. They have 

 seemed to think that practice must, in the nature of things, 

 improve the delicacy of discernment, and have let the 

 matter rest. At most they have said : " Attention accounts 

 for it ; we attend more to habitual things, and what we at- 

 tend to we perceive more minutely." This answer is true, 

 but too general ; it seems to me that we can be a little more 

 precise. 



There are at least tiuo distinct causes which we can see at 

 work whenever experience improves discrimination : 



First, the terms whose difference comes to be felt con- 

 tract disparate associates and these help to drag them 

 apart. 



Second, the difference reminds us of larger differences 

 of the same sort, and these help us to notice it. 



Let us study the first cause first, and begin by suppos- 

 ing two compounds, of ten elements apiece. Suppose no one 

 element of either compound to differ from the correspond- 

 ing element of the other compound enough to be distin- 

 guished from it if the two are compared alone, and let the 

 amount of this imperceptible difference be called equal to 

 1. The compounds will differ from each other, however, 

 in ten different ways ; and, although each difference by it- 

 self might pass unperceived, the total difference, equal to 

 10, may very well be sufficient to strike the sense. In a 

 word, increasing tlie number of ^points' involved in a difference, 

 may excite our discrimination as effectually as increasing the 

 amount of difference at any one point. Two men whose mouth, 

 nose, eyes, cheeks, chin, and hair, all differ slightly, will be 

 as little confounded by us, as two appearances of the same 

 man one with, and the other without, a false nose. The 

 only contrast in the cases is that we can easily name the 

 point of difference in the one, whilst in the other we cannot. 



Two things, then, B and C, indistinguishable when 

 compared together alone, may each contract adhesions 

 with different associates, and the compounds thus formed 



