590 THE POPULAR SCIENCE MONTHLY. 



forms of ordinary Mixed Association which lie nearest to Pure As- 

 sociation by Contiguity, which associate of the interesting item shall 

 emerge must be called largely a matter of accident — accident, that is, 

 for our intelligence. No doubt it is determined by cerebral causes, 

 but they are too subtile and shifting for our analysis. 



In Partial or Mixed Association we have all along supposed that 

 the interesting portion of the disappearing thought was of consider- 

 able extent, was sufficiently complex to constitute by itself a concrete 

 object. Sir William Hamilton relates that after thinking of Ben 

 Lomond he found himself thinking of the Prussian system of educa- 

 tion, and discovered that the links of association were a German gen- 

 tleman whom he had met on Ben Lomond, Germany, etc. The inter- 

 esting part of Ben Lomond, the part operative in determining the 

 train of his ideas was the complex image of a particular man. But 

 now let us suppose that that selective agency of interested attention, 

 which may convert in the way we have seen complete contiguous 

 association into partial association — let us suppose that it refines itself 

 still further and accentuates a portion of the passing thought, so small 

 as to be no longer the image of a concrete thing, but only of an ab- 

 stract quality or property. Let us, moreover, suppose that the part 

 thus accentuated persists in consciousness (or, in cerebral terms, has 

 its brain - process excited) after the other portions of the thought 

 have faded. This small surviving portion will then surround itself 

 with its own associates after the fashion we have already seen, and 

 the relation between the new thought and the faded one will be a 

 relation of similarity. The pair of thoughts will form an instance of 

 what is called " Association by Similarity." To make this perfectly 

 plain we must understand exactly what constitutes similarity between 

 two things. The moon is similar to a gas-jet, it is also similar to a 

 foot-ball ; but a gas-jet and a foot-ball are not similar to each other. 

 When we affirm the similarity of two things, we should always say in 

 what respect it obtains. Moon and gas-jet are similar in respect of 

 luminosity, and nothing else ; moon and foot-ball in respect of rotun- 

 dity, and nothing else. Foot-ball and gas-jet are in no respect similar 

 — that is, they possess no common point, no identical attribute. Ob- 

 jects are really identical with each other in that point with respect to 

 which they are called similar. Similarity is partial identity. When 

 the same attribute appears in two phenomena, though it be their only 

 common property, the two phenomena are similar in so far forth. To 

 return now to our associated representations. If the thought of the 

 moon is succeeded by the thought of a foot-ball, and that by the 

 thought of one of Mr. Vanderbilt's railroads, it is because the attri- 

 bute rotundity in the moon broke away from all the rest and sur- 

 rounded itself with an entirely new set of companions — elasticity, 

 leathery integument, swift mobility in obedience to human caprice, 

 etc. ; and because the last-named attribute in the foot-ball in turn 



