CHAPTEE X. 



OF PLURALITY OF CAUSES; AND OF THE INTERMIXTURE 

 OF EFFECTS. 



1. IN the preceding exposition of the four methods of 

 observation and experiment, by which we contrive to distin 

 guish among a mass of coexistent phenomena the particular 

 effect due to a given cause, or the particular cause which gave 

 birth to a given effect ; it has been necessary to suppose, in 

 the first instance, for the sake of simplification, that this ana 

 lytical operation is encumbered by no other difficulties than 

 what are essentially inherent in its nature ; and to represent 

 to ourselves, therefore, every effect, on the one hand as con 

 nected exclusively with a single cause, and on the other hand 

 as incapable of being mixed and confounded with any other 

 coexistent effect. We have regarded abode, the aggregate 

 of the phenomena existing at any moment, as consisting of 

 dissimilar facts, a, b, c, d, and e, for each of which one, and 

 only one, cause needs be sought; the difficulty being only 

 that of singling out this one cause from the multitude of 

 antecedent circumstances, A, B, C, D, and E. The cause 

 indeed may not be simple ; it may consist of an assemblage of 

 conditions; but we have supposed that there was only one 

 possible assemblage of conditions, from which the given effect 

 could result. 



If such were the fact, it would be comparatively an easy 

 task to investigate the laws of nature. But the supposition 

 does not hold, in either of its parts. In the first place, it is 

 not true that the same phenomenon is always produced by 

 the same cause : the effect a may sometimes arise from A, 

 sometimes from B. And, secondly, the effects of different 

 causes are often not dissimilar, but homogeneous, and marked 

 out by no assignable boundaries from one another : A and B 



