THE EXTERNAL WORLD 83 



which is possible at our present level is, therefore, only 

 that degree of verification which is possible by one man's 

 unaided observations, which will not carry us very far 

 towards the establishment of a whole science. 



Before proceeding further, let us summarise the argu- 

 ment so far as it has gone. The problem is : " Can the 

 existence of anything other than our own hard data be 

 inferred from these data ? " It is a mistake to state the 

 problem in the form : " Can we know of the existence of 

 anything other than ourselves and our states ? " or : " Can 

 we know of the existence of anything independent of 

 ourselves ? ' because of the extreme difficulty of defining 

 " self ' ' and " independent ' ' precisely. The felt passivity 

 of sensation is irrelevant, since, even if it proved anything, 

 it could only prove that sensations are caused by sensible 

 objects. The natural naive belief is that things seen 

 persist, when unseen, exactly or approximately as they 

 appeared when seen ; but this belief tends to be dispelled 

 by the fact that what common sense regards as the appear- 

 ance of one object changes with what common sense 

 regards as changes in the point of view and in the inter- 

 vening medium, including in the latter our own sense- 

 organs and nerves and brain. This fact, as just stated, 

 assumes, however, the common-sense world of stable 

 objects which it professes to call in question ; hence, 

 before we can discover its precise bearing on our problem, 

 we must find a way of stating it which does not involve 

 any of the assumptions which it is designed to render 

 doubtful. What we then find, as the bare outcome of 

 experience, is that gradual changes in certain sense-data 

 are correlated with gradual changes in certain others, or 

 (in the case of bodily motions) with the other sense-data 

 themselves. 



The assumption that sensible objects persist after they 



