PLURALITY OF CAUSES. 509 



plete and rigorous induction. Not so, however, with 

 the Method of Agreement. The conclusions which 

 that yields, when the number of instances compared is 

 small, are of no real value, except as, in the character 

 of suggestions, they may lead either to experiments 

 bringing them to the test of the Method of Difference, 

 or to reasonings which may explain and verify them 

 deductively. 



It is only when the instances, being indefinitely 

 multiplied and varied, continue to suggest the same 

 result, that this result acquires any high degree of 

 independent value. If there are but two instances, 

 ABC and A D E, although these instances have no 

 antecedent in common except A, yet as the effect 

 may possibly have been produced in the two cases by 

 different causes, the result is at most only a slight 

 probability in favour of A; there may be causation, 

 but it is almost equally probable that there was only, 

 as the expression is, a coincidence. But the oftener 

 we repeat the observation, varying the circumstances, 

 the more we advance towards a solution of this doubt. 

 For if we try A F G, A H K, &c., all entirely unlike 

 one another except in containing the circumstance 

 A, and if we find the effect a entering into the result 

 hi all these cases, we must suppose one of two 

 things, either that it is caused by A, or that it has as 

 many different causes as there are instances. With 

 each addition, therefore, to the number of instances, 

 the presumption is strengthened in favour of A. The 

 inquirer, of course, will not neglect, if an opportunity 

 present itself, to exclude A from some one of these 

 combinations, from A H K for instance, and by 

 trying H K separately, appeal to the Method of 

 Difference in aid of the Method of Agreement. By 

 the former method alone can it be ascertained that A 



