250 INDUCTION. 



an ulterior original distinction, and the measure of its amount. But 

 the strongest assertors of- such supposed differences have hitherto been 

 very negligent of providing themselves with these necessary logical 

 Conditions of the establishment of their doctrine. 



The spirit of the Method of Residues being, it is hoped, sufficiently 

 intelligible from these examples, and the other three methods having 

 been so aptly exemplified in the inductive processes which produced 

 the Theory of Dew, we may here close our exposition of the four 

 methods, considered as employed in the investigation of the simpler 

 and more elementary order of the combinations of phenomena. 



CHAPTER X. 



OF PLURALITV 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 neces- 

 sary to suppose, in the first instance, for the sake of simplification, that 

 this analytical operation is encumbered by no other difficulties than 

 what are essentially inherent in its nature; and to represent to our- 

 selves, therefore, every effect, on the one hand as connected exclu- 

 sively with a single cause, and On the other hand as incapable of being 

 mixed and confounded with any other coexistent effect. We have re- 

 garded ahcdc, the aggregate of the phenomena existing at any mo- 

 ment, as consisting of tlissimilar 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 fi-om the multitude of antecedent circum- 

 stances, A,B, C, D, and E. 



If such were the fact, it would be comparatively an easy task to in- 

 vestigate 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 phe- 

 nomenon 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 hornogeneous, and 

 marked out by no assignable boundaries fi-om one another : A and B 

 may produce not a and h, 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 cir- 

 cumstances ; 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 ti'ue, then, that one effect must be connected with only one 

 cause, or assemblage of conditions ; that each phenomenon can be pro- 

 duced 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 ante- 

 cedents. Many causes may produce motion ; many causes may pro- 



