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CHAPTER 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 distinguish 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 connected 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, 6, c, d, and e t for each of which 

 one, and only one, cause needs be sought; the diifi- 

 culty being only that of singling out this one cause 

 from the multitude of antecedent circumstances, A, B, 

 C, D, and E. 



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 pheno- 

 menon 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 



