VIII 



THE RELATION OF SENSE-DATA 

 TO PHYSICS 



I. THE PROBLEM STATED 



PHYSICS is said to be an empirical science, based 

 upon observation and experiment. 



It is supposed to be verifiable, i.e. capable of calcu- 

 lating beforehand results subsequently confirmed by 

 observation and experiment. 



What can we learn by observation and experiment ? 



Nothing, so far as physics is concerned, except imme- 

 diate data of sense : certain patches of colour, sounds, 

 tastes, smells, etc., with certain spatio-temporal rela- 

 tions. 



The supposed contents of the physical world are prima 

 facie very different from these : molecules have no colour, 

 atoms make no noise, electrons have no taste, and cor- 

 puscles do not even smell. 



If such objects are to be verified, it must be solely 

 through their relation to sense-data : they must have 

 some kind of correlation with sense-data, and must be 

 verifiable through their correlation alone. 



But how is the correlation itself ascertained ? A cor- 

 relation can only be ascertained empirically by the cor- 

 related objects being constantly found together. But in 

 our case, only one term of the correlation, namely, the 

 sensible term, is ever found : the other term seems essen- 

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