LAW OF CAUSATION. 877 



involves the idea of necessity. If there be any meaning 

 which confessedly belongs to the term necessity, it is uncon- 

 ditionalness. 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. 



Invariable sequence, therefore, is not synonymous with 

 causation, unless the sequence, besides being invariable, is 

 unconditional. There are sequences, as uniform in past 

 experience as any others whatever, which yet we do not re- 

 gard as cases of causation, but as conjunctions in some sort 

 accidental. Such, to an accurate thinker, is that of day and 

 night. The one might have existed for any length of time, 

 and the other not have followed the sooner for its existence ; 

 it follows only if certain other antecedents exist ; and where 

 those antecedents existed, it would follow in any case. No 

 one, probably, ever called night the cause of day ; mankind 

 must so soon have arrived at the very obvious generalization, 

 that the state of general illumination which we call day would 

 follow from the presence of a sufficiently luminous body, 

 whether darkness had preceded or not. 



We may define, therefore, the cause of a phenomenon, to 

 be the antecedent, or the concurrence of antecedents, on 

 which it is invariably and unconditionally consequent. Or if 

 we adopt the convenient modification of the meaning of the 

 word cause, which confines it to the assemblage of positive 

 conditions without the negative, then instead of " uncon- 

 ditionally," we must say, "subject to no other than negative 

 conditions." 



To some it may appear, that the sequence between night 

 and day being invariable in our experience, we have as much 

 ground in this case as experience can give in any case, for 

 recognising the two phenomena as cause and effect ; and that 



