346 



im>tTCTlON. 



nomena. so conjoined must be in some 

 way connected through their causes. 



There is, however, no euch test. 

 A coincidence may occur again and 

 again, and yet be only casual. Nay, 

 it would be inconsistent with what 

 we know of the order of nature to 

 doubt that every casual coincidence 

 will sooner or later be repeated, as 

 long as the phenomena between which 

 it occurred do not cease to exist, or to 

 be reproduced. The recurrence, there- 

 fore, of the same coincidence more 

 than once, or even its frequent re- 

 currence, does not prove that it is an 

 instance of any law ; does not prove 

 that it is not casual, or, in common 

 language, the effect of chance. 



And yet, when a coincidence can- 

 not be deduced from known laws, nor 

 proved by experiment to be itself a 

 case of causation, the frequency of its 

 occurrence is the only evidence from 

 which we can infer that it is the 

 result of a law. Not, however, its 

 absolute frequency. The question is 

 not whether the coincidence occurs 

 often or seldom, in the ordinary sense 

 of those terms ; but whether it occurs 

 more often than chance will account 

 for ; more often than might rationally 

 be expected if the coincidence were 

 casual. We have to decide, therefore, 

 what degree of frequency in a coinci- 

 dence chance will account for. And 

 to this there can be no general answer. 

 We can only state the principle by 

 which the answer must be determined: 

 the answer itself will be different in 

 every different case. 



Suppose that one of the phenomena, 

 A, exists always, and the other pheno- 

 menon, B, only occasionally ; it fol- 

 lows that every instance of B will be 

 an instance of its coincidence with A, 

 and yet the coincidence will be merely 

 casual, and not the result of any con- 

 nection between them. The fixed 

 stars have been constantly in exist- 

 ence since the beginning of human 

 experience, and all phenomena that 

 have come under human observation 

 have, in every single instance, co- 

 existed with them ; yet this coinci- 



dence, though equally invariable with 

 that which exists between any of 

 those phenomena and its own cause, 

 does not prove that the stars are its 

 cause, nor that they are in any wise 

 connected with it. As strong a case 

 of coincidence, therefore, as can pos- 

 sibly exist, and a much stronger one 

 in point of mere frequency than most 

 of those which prove laws, does not 

 here prove a law. Why? because, 

 since the stars exist always, they 

 must co-exist with every other phe- 

 nomenon, whether connected with 

 them by causation or not. The uni- 

 formity, great though it be, is no 

 greater than would occur on the sup- 

 position that no such connection exists. 

 On the other hand, suppose that 

 we were inquiring whether there be 

 any connection between rain and any 

 particular wind. Rain, we know, 

 occasionally occurs with every wind ; 

 therefore the connection, if it exists, 

 cannot be an actual law : but still, 

 rain may be connected with some 

 particular wind through causation ; 

 that is, though they cannot be always 

 effects of the same cause, (for if so, 

 they would regularly co-exist,) there 

 may be some causes common to the 

 two, so that in so far as either is pro- 

 duced bj' those common causes, they 

 will, from the laws of the causes, be 

 found to co-exist. How, then, shall 

 we ascertain this ? The obvious 

 answer is, by observing whether rain 

 occurs with one wind more frequently 

 than with any other. That, however, 

 is not enough ; for perhaps that one 

 wind blows more frequently than any 

 other ; so that its blowing more fre- 

 quently in rainy weather is no more 

 than would happen, although it had 

 no connection with the causes of rain, 

 provided it were not connected with 

 causes adverse to rain. In England, 

 westerly winds blow during about 

 twice as great a portion of the yeai- 

 as easterly. If, therefore, it rains 

 only twice as often with a westerly 

 as with an easterly wind, we have no 

 reason to infer that any law of nature 

 is concerned in the coincidence. If 



