LAW OF CAUSATION. 411 



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 upon 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 although no case should have ever 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 regard as cases of causation, but 

 as conjunctions, in some sort accidental. Such, to a 

 philosopher, 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 obvi- 

 ous generalization, that the state of general illumina- 

 tion which we call day would follow the presence of a 

 sufficiently luminous body, whether darkness had pre- 

 ceded or not. 



We may define, therefore, the cause of a phenome- 

 non to be the antecedent, or the concurrence of ante- 

 cedents, upon which it is invariably and unconditionally 

 consequent. Or if we adopt the convenient modifi- 

 cation of the meaning of the word cause, which con- 

 fines it to the assemblage of positive conditions, with- 

 out the negative, then instead of " unconditionally," 

 we must say, " subject to no other than negative 

 conditions." 



