THE FACTS OF SCIENCE 71 



purely mental conception of sanrieness of weight. Is it 

 not clear that the reality of the blackboard consisted for 

 us in the permanent grouping together of certain sense- 

 impressions, and that that reality has disappeared for 

 ever, except as a group of stored sense-impressions ? 



\ I 5 . — Individuality 



Let us look again at this matter from a slightly 

 different standpoint. Let us consider a personal friend, 

 and then suppose his height, his figure, the familiar 

 features of his face changed ; let his entire round of 

 physical characteristics be profoundly modified, or vanish 

 altogether. Next let us imagine his gifts, his prejudices, 

 the little weaknesses which really endear him to us, his 

 views on literature, politics, and social problems, all his 

 conceptions of human life removed or changed entirely. 

 In short, all the sense-impressions which constitute our 

 friend gone. Clearly the friend would have ceased for us 

 to be, his individuality would have disappeared. The 

 " reality " of the friend consists for us, not in some shadowy 

 " thing-in-itself," but in the persistency of the majority of 

 the group of sense-impressions by which we identify him. 

 We are accustomed to speak, for practical purposes, of 

 the boy and the man as the same individual, but the body 

 and mind have changed so enormously that the man 

 would probably feel the boy a perfect stranger if he were 

 brought into his presence. We experience an uncomfort- 

 able sense of strangeness in looking at portraits of our- 

 selves taken twenty or thirty years ago. The properties 

 of youth and man are, indeed, so widely different, that 

 though for practical purposes we call them the same 

 person, we suspect that they would cut each other if they 

 chanced to meet in the street. Clearly an individual is 

 not characterised by any sameness in the thing-in-itself, 

 but by the sameness in or permanency of a certain group- 

 ing of sense-impressions ; this is the basis of our identi- 

 fication. 



