THE EXTERNAL WORLD 81 



whatever object is visible beyond the empty sight-place 

 in the same line of sight has a different colour from what 

 it has when there is no tangible object in the intervening 

 touch-place ; and as we move the tangible object in 

 touch-space, the blue patch moves in sight-space. If 

 now we find a blue patch moving in this way in sight- 

 space, when we have no sensible experience of an 

 intervening tangible object, we nevertheless infer that, if 

 we put our hand at a certain place in touch-space, we 

 should experience a certain touch-sensation. If we are 

 to avoid non-sensible objects, this must be taken as the 

 whole of our meaning when we say that the blue 

 spectacles are in a certain place, though we have not 

 touched them, and have only seen other things rendered 

 blue by their interposition. 



I think it may be laid down quite generally that, in so 

 far as physics or common sense is verifiable, it must be 

 capable of interpretation in terms of actual sense-data 

 alone. The reason for this is simple. Verification con- 

 sists always in the occurrence of an expected sense-datum. 

 Astronomers tell us there will be an eclipse of the moon : 

 we look at the moon, and find the earth's shadow biting 

 into it, that is to say, we see an appearance quite different 

 from that of the usual full moon. Now if an expected 

 sense-datum constitutes a verification, what was asserted 

 must have been about sense-data ; or, at any rate, if part 

 of what was asserted was not about sense-data, then only 

 the other part has been verified. There is in fact a 

 certain regularity or conformity to law about the 

 occurrence of sense-data, but the sense-data that occur 

 at one time are often causally connected with those that 

 occur at quite other times, and not, or at least not very 

 closely, with those that occur at neighbouring times. If 

 I look at the moon and immediately afterwards hear a 



