PLURALITY OF CAUSES. 



285 



ing by persons eminent in physical 

 science, as soon as they are off the 

 ground on which they are conversant 

 with the facts, and not reduced to 

 judge only by the arguments ; and as 

 for educated persons in general, it 

 may be doubted if they are better 

 judges of a good or a bad induction 

 than they were before Bacon wrote. 

 The improvement in the results of 

 thinking has seldom extended to the 

 processes ; or has reached, if any pro- 

 cess, that of investigation only, not 

 that of proof. A knowledge of many 

 laws of nature has doubtless been ar- 

 rived at by framing hypotheses and 

 finding that the facts corresponded to 

 them ; and many errors have been 

 got rid of by coming to a knowledge 

 of facts which were inconsistent with 

 them, but not by discovering that the 

 mode of thought which led to the 

 errors was itself faulty, and might 

 have been known to be such inde- 

 pendently of the facts which disproved 

 the specific conclusion. Hence it is 

 that, while the thoughts of mankind 

 have on many subjects worked them- 

 selves practically right, the thin ^ 

 power remains as weak as ever ; and 

 on all subjects on which the facts 

 which would check the result are not 

 accessible, as in what relates to the 

 invisible world, and even, as has 

 been seen lately, to the visible world 

 of the planetary regions, men of the 

 greatest scientific acquirements argue 

 as pitiably as the merest ignoramus. 

 For though they have made many 

 sound inductions, they have not 

 learnt from them (and Dr. Whewell 

 thinks there is no necessity that they 

 should learn) the principles of induc- 

 tive evidence. 



CHAPTER X 



OP PLURALITY OF CATTSBS, AND OP THE 

 INTERMIXTURE OP EXPECTS. 



§ I. In the preceding exposition of 

 the four methods of observation and 

 experiment, by which we contrive to 

 distinguish among a mass of co-exis- 



tent phenomena the particular effect 

 due to a given cause, or the parti- 

 cular 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 analy- 

 tical operation is encumbered by no 

 other difficulties than what are essen- 

 tially 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 co-existent effect. We 

 have regarded a b c d e, the aggre- 

 gate of the phenomena existing at 

 any moment, as consisting of dissi- 

 milar facts, a, 6, 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 antece- 

 dent circumstances. A, B, C, D, and 

 E, The cause indeed may not be 

 simple ; it may consist of an assem- 

 blage of conditions ; but we have sup- 

 posed 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 inves- 

 tigate 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 may produce not a and b, but dif- 

 ferent portions of an effect a. The 

 obscurity and diflBculty of the inves- 

 tigation of the laws of phenomena is 

 singularly increased by the necessity 

 of adverting to these two circum- 

 stances — Intermixture of Effects and 

 Plurality of Causes. To the latter, 

 being the simpler of the two con- 

 siderations, we shall first direct our 

 attention. 



