PLURALITY OF CAUSES. 507 



out by no assignable boundaries from one another : A 

 and B may produce not a and &, 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 adverting 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 con- 

 ditions ; that each phenomenon 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 uniformity, any one of several antecedents, or 

 collections of antecedents. Many causes may pro- 

 duce motion : many causes may produce some kinds 

 of sensation : many causes may produce 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 our 

 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 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 com- 



