THE EXTERNAL WORLD 85 



only exists when it is seen, is still something quite 

 different from the seeing of it : the seeing of it is mental, 

 but the patch of colour is not. This confusion, however, 

 can be avoided without our necessarily abandoning the 

 theory we are examining. The objection to it, I think, 

 lies in its failure to realise the radical nature of the recon- 

 struction demanded by the difficulties to which it points. 

 We cannot speak legitimately of changes in the point of 

 view and the intervening medium until we have already 

 constructed some world more stable than that of moment- 

 ary sensation. Our discussion of the blue spectacles and 

 the walk round the table has, I hope, made this clear. 

 But what remains far from clear is the nature of the 

 reconstruction required. 



Although we cannot rest content with the above theory, 

 in the terms in which it is stated, we must nevertheless 

 treat it with a certain respect, for it is in outline the 

 theory upon which physical science and physiology are 

 built, and it must, therefore, be susceptible of a true 

 interpretation. Let us see how this is to be done. 



The first thing to realise is that there are no such 

 things as " illusions of sense." Objects of sense, even 

 when they occur in dreams, are the most indubitably real 

 objects known to us. What, then, makes us call them 

 unreal in dreams ? Merely the unusual nature of their 

 connection with other objects of sense. I dream that I 

 am in America, but I wake up and find myself in England 

 without those intervening days on the Atlantic which, 

 alas ! are inseparably connected with a " real " visit to 

 America. Objects of sense are called "real" when they 

 have the kind of connection with other objects of sense 

 which experience has led us to regard as normal ; when 

 they fail in this, they are called " illusions." But what 

 is illusory is only the inferences to which they give rise ; 



