ch.vi.] CAUSATION. 153 



hours, when the sky is clear, we have an cxperimentum cruris 

 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 invariable 

 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." 



Furthermore let it be noted that " 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 unconditional sequences, there 

 will result a much greater number of conditional ones. 

 Certain causes being given, that is, certain antecedents which 

 are unconditionally followed by certain consequents; the 

 mere coexistence of these causes will give rise to an un- 

 limited number of additional uniformities. If two causes 

 exist together, the effects of both will exist together ; and if 

 many causes coexist, these causes will give rise to new 

 effects, accompanying or succeeding one another in some 

 particular order, which order will be invariable while the 

 causes continue to coexist, 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, 



