INTERMIXTURE OF EFFECTS. 531 



namely, by comparing, not the same case at two 

 different periods, but different cases, this in the pre- 

 sent instance is quite chimerical. In phenomena so 

 complicated it is questionable if two cases similar in 

 all respects but one ever occurred ; and were they to 

 occur, we could not possibly know that they were so 

 exactly similar. 



Anything like a scientific use of the method of 

 experiment, in these complicated cases, is therefore 

 out of the question. We can in the most favourable 

 cases only discover, by a succession of trials, that a 

 certain cause is very often followed by a certain effect. 

 For, in one of these conjunct effects, the portion 

 which is determined by any one of the influencing 

 agents, is generally, as we before remarked, but small; 

 and it must be a more potent cause than most, if even 

 the tendency which it really exerts is not thwarted by 

 other tendencies in nearly as many cases as it is 

 fulfilled. 



If so little can be done by the experimental 

 method to determine the conditions of an effect of 

 many combined causes, in the case of medical science, 

 still less is this method applicable to a class of phe- 

 nomena more complicated than even those of phy- 

 siology, the phenomena of politics and history. 

 There, Plurality of Causes exists in almost boundless 

 excess, and the effects are, for the most part, inex- 

 tricably interwoven with one another. To add to the 

 embarrassment, most of the inquiries in political 

 science relate to the production of effects of a most 

 comprehensive description, such as the public wealth, 

 public security, public morality, and the like : results 

 liable to be affected directly or indirectly either in plus 

 or in minus by nearly every fact which exists, or 

 event which occurs, in human society. The vulgar 



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