246 INDUCTION. 



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 

 conditional and anxjther unconditional. When we judge that the succes- 

 sion of night and day is a derivative sequence, depending on something 

 else, we proceed on grounds of experience. It is the evidence of experi- 

 ence which convinces us that day could equally exist without being fol- 

 lowed by night, and that night could equally exist without being followed 

 by day. To say that these beliefs are " not generated by our mere ob- 

 servation of sequence,"* is to forget that twice in every twenty-four hours, 

 when the sky is clear, we have an experimentum 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 antecedent which is only conditionally invariable, is not the in- 

 variable 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 cor- 

 rectly represent all possible cases, the hitherto invariable antecedent is not 

 accounted the cause ; but why ? Because we are not sure that it is the in- 

 variable antecedent. 



Such cases of sequence as that of day and night not only do not contra- 

 dict the doctrine which resolves causation into invariable sequence, but are 

 necessarily implied in that doctrine. It is evident, that from a limited 

 number of unconditional sequences, there will result a much greater num- 

 ber of conditional ones. Certain causes being given, that is, certain ante- 

 cedents which are unconditionally followed by certain consequents; the 

 mere co-existence of these causes will give rise to an unlimited number 

 of additional uniformities. If two causes exist together, the effects of both 

 will exist together ; and if many causes co-exist, these causes (by what we 

 shall term hereafter the intermixture of their laws) will give rise to new ef- 

 fects, accompanying or succeeding one another in some particular order, 

 which order will be invariable while the causes continue to co-exist, but no 

 longer. The motion of the earth in a given orbit round the sun, is a series 

 of changes which follow one another as antecedents and consequents, and 

 will continue to do so while the sun's attraction, and the force with which 

 the earth tends to advance in a direct line through space, continue to co- 

 exist in the same quantities as at present. But vary either of these causes, 

 and this particular succession of motions would cease to take place. The 

 series of the earth's motions, therefore, though a case of sequence invari- 

 able within the limits of human experience, is not a case of causation. It 

 is not unconditional. 



This distinction between the relations of succession which, so far as we 

 know, are unconditional, and those relations, whether of succession or of 

 co-existence, which, like the earth's motions, or the succession of day and 

 night, depend on the existence or on the co-existence of other antecedent 

 facts — corresponds to the great division which Dr. Whewell and other 

 writers have made of the field of science, into the investigation of what 



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



