378 INDUCTION. 



to say that more is necessary to require a belief that the 

 succession is unconditional, or in other words that it would 

 be invariable under all changes of circumstances, is to acknow- 

 ledge in causation an element of belief not derived from 

 experience. The answer to this is, that it is experience itself 

 which teaches us that one uniformity of sequence is con- 

 ditional and another unconditional. When we judge that the 

 succession of night and day is a derivative sequence, depending 

 on something else, we proceed on grounds of experience. It 

 is the evidence of experience which convinces us that day 

 could equally exist without being followed by night, and that 

 night could equally exist without being followed by day. To 

 say that these beliefs are " not generated by our mere obser- 

 vation of sequence,"* is to forget that twice in every twenty- 

 four hours, when the sky is clear, we have an experimen- 

 tum crucis that the cause of day is the sun. We have an 

 experimental knowledge of the sun which justifies us on 

 experimental grounds in concluding, that if the sun were 

 always above the horizon there would be day, though there 

 had been no night, and that if the sun were always below the 

 horizon there would be night, though there had been no day. 

 We thus know from experience that the succession of night 

 and day is not unconditional. Let me add, that the antece- 

 dent which is only conditionally invariable, is not the inva- 

 riable antecedent. Though a fact may, in experience, have 

 always been followed by another fact, yet if the remainder of 

 our experience teaches us that it might not always be so 

 followed, or if the experience itself is such as leaves room for 

 a possibility that the known cases may not correctly represent 

 all possible cases, the hitherto invariable antecedent is not 

 accounted the cause; but why ? Because we are not sure that 

 it is the invariable antecedent. 



Such cases of sequence as that of day and night not only 

 do not contradict the doctrine which resolves causation into 

 invariable sequence, but are necessarily implied in that 

 doctrine. It is evident, that from a limited number of uncon- 



* Second Burnett Prize Essay, by Principal Tulloch, p. 25. 



