THE EXTERNAL WORLD 79 



But we have still not reduced our statement completely 

 to what is actually given in sense. We have fallen into 

 the assumption that the object of which we are conscious 

 when we touch the blue spectacles still exists after we have 

 ceased to touch them. So long as we are touching them, 

 nothing except our finger can be seen through the part 

 touched, which is the only part where we immediately 

 know that there is something. If we are to account for 

 the blue appearance of objects other than the spectacles, 

 when seen through them, it might seem as if we must 

 assume that the spectacles still exist when we are not 

 touching them ; and if this assumption really is neces- 

 sary, our main problem is answered : we have means of 

 knowing of the present existence of objects not given in 

 sense, though of the same kind as objects formerly given 

 in sense. 



It may be questioned, however, whether this assump- 

 tion is actually unavoidable, though it is unquestionably 

 the most natural one to make. We may say that the 

 object of which we become aware when we touch the 

 spectacles continues to have effects afterwards, though 

 perhaps it no longer exists. In this view, the supposed 

 continued existence of sensible objects after they have 

 ceased to be sensible will be a fallacious inference from 

 the fact that they still have effects. It is often supposed 

 that nothing which has ceased to exist can continue to 

 have effects, but this is a mere prejudice, due to a wrong 

 conception of causality. We cannot, therefore, dismiss 

 our present hypothesis on the ground of a priori impossi- 

 bility, but must examine further whether it can really 

 account for the facts. 



It may be said that our hypothesis is useless in the 

 case when the blue glass is never touched at all. How, 

 in that case, are we to account for the blue appearance of 



