a 



COMMONSENSE" OBJECTIONS 17 



obtained with no precautions, if it just comes into our 

 heads unsought, then it is obviously true and to doubt 

 it would be flying in the face of commonsense ! We 

 have a sort of impression (although we do not like 

 to acknowledge it) that the mind puts out a feeler into 

 space to ascertain directly where each familiar object is. 

 That is nonsense; our commonsense knowledge of location 

 is not obtained that way. Strictly it is sense knowledge, 

 not commonsense knowledge. It is partly obtained 

 by touch and locomotion; such and such an object 

 is at arm's length or a few steps away. Is there 

 any essential difference (other than its crudity) between 

 this method and scientific measurements with a scale? 

 It is partly obtained by vision — a crude version of 

 scientific measurement with a theodolite. Our common 

 knowledge of where things are is not a miraculous 

 revelation of unquestionable authority; it is inference 

 from observations of the same kind as, but cruder than, 

 those made in a scientific survey. Within its own limits 

 of accuracy the scheme of location of objects that I am 

 instinctively "aware" of is the same as my scientific 

 scheme of location, or frame of space. 



When we use a carefully made telescope lens and a 

 sensitised plate instead of the crystalline lens and retina 

 of the eye we increase the accuracy but do not alter the 

 character of our survey of space. It is by this increase 

 of refinement that we have become "aware" of certain 

 characteristics of space which were not known to our 

 ape-like ancestor when he instituted the common ideas 

 that have come down to us. His scheme of location 

 works consistently so long as there is no important 

 change in his motion (a few miles a second makes no 

 appreciable difference) ; but a large change involves a 

 transition to a different system of location which is like- 



