SUBJECTIVE AND OBJECTIVE METHODS 



position of a specific hidden power in the cause, 

 which constrains the effect to follow. Hume 

 denied the existence of any such specific hidden 

 power, and his denial was also metaphysical, 

 because neither the presence nor the absence 

 of such a specific power is a necessary inference 

 from the phenomena. If we would keep clear 

 of metaphysics, we must in such a case neither 

 affirm nor deny concerning a subject which lies 

 utterly beyond our reach. Physics knows no- 

 thing of causation except that it is the invariable 

 and unconditional sequence of one event upon 

 another: whether the one event, in a meta- 

 physical sense, constrains the other to follow it 

 or not we cannot tell. Physics knows nothing 

 of such constraint — neither that it exists, nor 

 that it does not exist. 



For the moment I have, somewhat too freely, 

 used the word " physics " as synonymous with 

 " science ; '* for I have aimed at bringing out 

 the fundamental distinction between metaphy- 

 sics and science, which is this : A scientific ex- 

 planation is a hypothesis which admits of veri- 

 fication^ — // can be either proved or disproved; 

 while a metaphysical explanation is a hypothesis 

 which does not admit of verification^ — it can 

 neither be proved nor disproved, Newton's hy- 

 pothesis of gravitation, to account for the plan- 

 etary motions, was strictly scientific ; and so 

 was Descartes' hypothesis of vortices, to account 



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