ON THE NOTION OF CAUSE 207 



susceptible of material determinants is also susceptible 

 of mental determinants ; thus a mechanical system may 

 be determined by sets of volitions, as well as by sets of 

 material facts. It would seem, therefore, that the reasons 

 which make people dislike the view that volitions are 

 mechanically determined are fallacious. 



(4) The notion of necessity, which is often associated 

 with determinism, is a confused notion not legitimately 

 deducible from determinism. Three meanings are 

 commonly confounded when necessity is spoken of : 



(a) An action is necessary when it will be performed 

 however much the agent may wish to do otherwise. 

 Determinism does not imply that actions are necessary 

 in this sense. 



(/3) A propositional function is necessary when all its 

 values are true. This sense is not relevant to our present 

 discussion. 



(y) A proposition is necessary with respect to a given 

 constituent when it is the value, with that constituent as 

 argument, of a necessary propositional function, in other 

 words, when it remains true however that constituent 

 may be varied. In this sense, in a deterministic system, 

 the connection of a volition with its determinants is 

 necessary, if the time at which the determinants occur be 

 taken as the constituent to be varied, the time-interval 

 between the determinants and the volition being kept 

 constant. But this sense of necessity is purely logical, 

 and has no emotional importance. 



We may now sum up our discussion of causality. We 

 found first that the law of causality, as usually stated by 

 philosophers, is false, and is not employed in science. We 

 then considered the nature of scientific laws, and found 

 that, instead of stating that one event A is always followed 



