644 PSYCHOLOGY. 



I need not consult the world of experience at all ; the mere 

 ideas suffice. Wimt I mean by black difi'eis from ivhat 1 

 mean by white, whether such colors exist extra mentem meam, 

 or not. If they ever do so exist, they will differ. White 

 things may blacken, but the black of them will differ from 

 the white of them, so long as I mean anything definite bj 

 these three words.* 



/ shall noiv in ivhat follows call all propositions which ex- 

 press time- and, space-relations empirical propositions ; and 1 

 shall give the name of rationed propositions to all propositions 

 which express the results of a comparison. The latter denomi- 

 nation is in a sense arbitrar^^, for resemblance and differ- 

 ence are not usually held to be the only rational relations 

 between things. I will next proceed to show, however, 

 how many other rational relations commonly supposed dis- 

 tinct can be resolved into these, so that my definition of 

 rational propositions will end, I trust, by proving less arbi- 

 trary than it now appears to be. 



SERIES OP EVEIvT DIFFERENCE AND MEDIATE COMPARISON. 



In Chapter XII we saw that the mind can at successive 

 moments mean the same, and that it gradually comes into 

 possession of a stock of permanent and fixed meanings, 

 ideal objects, or conceptions, some of which are universal 

 qualities, like the black and white of oui example, and some, 

 individual things. We now see that not only are the objects 

 permanent mental possessions, but the results of their com- 

 parison are permanent too. The objects and their differ- 

 ences together form an immutable system. The same ob- 

 jects, compared in the same ivay, ahvays give the same results ; 



* "Though a man in a fever should from sugar have a bitter taste which 

 at another time would produce a sweet one, yet the idea of bitter in that 

 man's mind would be as clear and distinct from the idea of sweet as if he 

 had tasted only gall. Nor does it make any more confusion between the 

 two ideas of sweet and bitter that the same sort of body produces at one 

 time one and at another time another idea by the taste, than it makes a 

 confusion in two ideas of white and sweet, or white and round, that the 

 same piece of sugar produces them both in the mind at the same time. * 

 Locke's Essay, bk. ir. ch. xi. ^ 3. 



