CAUSATION 



variable throughout the whole course of human 

 experience, but which are not regarded as causal 

 sequences. Ever since there have been con- 

 scious minds to interpret phenomena, day has 

 followed night, and night has followed day, and 

 yet no one would say that day causes night, or 

 that night causes day. In order to include such 

 cases as this, we must limit still further our de- 

 finition of causation. The sequence must be 

 unconditional as well as invariable. This, as Mr. 

 Mill observes, " is what writers mean when they 

 say that the notion of cause involves the idea 

 of necessity. If there be any meaning which 

 confessedly belongs to the term ' necessity,' it 

 is unconditionalness } That which is necessary, 

 that which must be, means that which will be, 

 whatever supposition we may make in regard 

 to all other things. The succession of day and 

 night evidently is not necessary in this sense. 

 It is conditional on the occurrence of other 

 antecedents. That which will be followed by a 

 given consequent when, and only when, some 

 third circumstance also exists, is not the cause, 

 even though no case should ever have occurred 

 in which the phenomenon took place without 

 it." Now, either day or night " might have 

 existed for any length of time, and the other 

 not have followed the sooner for its existence : 



^ This, it will be seen, agrees with Mr. Lewes' s admirable 

 view of Necessity, cited above in chapter iii. 

 223 



