PLURALITY OF CAUSES. 483 



may produce not a and b, but different portions of an effect a. 

 The obscurity and difficulty of the investigation of the laws of 

 phenomena is singularly increased by the necessity of ad- 

 verting to these two circumstances ; Intermixture of Effects, 

 and Plurality of Causes. To the latter, being the simpler of 

 the two considerations, we shall first direct our attention. 



It is not true, then, that one effect must be connected with 

 only one cause, or assemblage of conditions ; that each phe- 

 nomenon can be produced only in one way. There are often 

 several independent modes in which the same phenomenon 

 could have originated. One fact may be the consequent in 

 several invariable sequences; it may follow, with equal uni- 

 formity, any one of several antecedents, or collections of ante- 

 cedents. Many causes may produce motion: many causes 

 may produce some kinds of sensation : many causes may pro- 

 duce death. A given effect may really be produced by a 

 certain cause, and yet be perfectly capable of being produced 

 without it. 



2. One of the principal consequences of this fact of 

 Plurality of Causes is, to render the first of the inductive 

 methods, that of Agreement, uncertain. To illustrate that 

 method, we supposed two instances, ABC followed by a b c, 

 and A D E followed by a d e. From these instances it might 

 apparently be concluded that A is an invariable antecedent of 

 a, and even that it is the unconditional invariable antecedent, 

 or cause, if we could be sure that there is no other antecedent 

 common to the two cases. That this difficulty may not stand 

 in the way, let us suppose the two cases positively ascertained 

 to have no antecedent in common except A. The moment, 

 however, that we let in the possibility of a plurality of causes, 

 the conclusion fails. For it involves a tacit supposition, that 

 a must have been produced in both instances by the same 

 cause. If there can possibly have been two causes, those two 

 may, for example, be C and E : the one may have been the 

 cause of a in the former of the instances, the other in the 

 latter, A having no influence in either case. 



Suppose, for example, that two great artists, or great philo- 

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