forms of ordinary Mixed Association which lie nearest to Pure Association 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 considerable 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 education, and discovered that the links of association were a German gentleman whom he had met on Ben Lomond, Germany, etc. The interesting 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 abstract 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 rotundity, and nothing else. Foot-ball and gas-jet are in no respect similar—that is, they possess no common point, no identical attribute. Objects 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 attribute rotundity in the moon broke away from all the rest and surrounded 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
