NECESSARY SUCCESSION 337 



is merely to describe phenomena and record their coexistences 

 and sequences. 



567. On the other hand, to the common-sense thinker, who 

 supposes that both minds and material bodies exist and that the 

 former can be aware of the latter, causation implies more than 

 mere invariable succession. It implies necessary succession. 1 

 For, believing that material bodies have properties or qualities 

 which bring them into certain relations with one another, he 

 believes also that, given these properties and relations, certain 

 consequences must follow. Thus, though he perceives that day 

 and night invariably succeed one another, yet he repudiates the 

 idea that they alternately cause each other. He knows of no 

 property in the one which can cause the other. On the contrary, 

 he supposes that day and night succeed because the round, 

 opaque, material earth rotates and so presents successive 

 parts of itself to a luminous body the sun. Given these 

 conditions, the non-occurrence of day and night would be in- 

 conceivable to him. Given the absence of the opacity of the 

 earth, or of its rotation, or of the luminosity of the sun, and he 

 would be forced to believe that day or night would be eternal, 

 though he has no experience of such a condition. A single 

 chemical experiment will convince him that a certain substance 

 exists because two or more elements have united ; but no amount 

 of experience will convince him that fine weather is the cause of 

 the rain that succeeds it. In other words, there is for him a 

 distinction between post hoc and propter hoc. 



1 See 578. 



22 



