INTERMIXTURE OF EFFECTS. 499 



of nomenclature and arrangement. An effect of precisely the 

 same kind, and arising from the same cause, ought not to be 

 placed in two different categories, merely as there does or does 

 not exist another cause preponderating over it."* 



6. We have now to consider according to what method 

 these complex effects, compounded of the effects of many 

 causes, are to he studied ; how we are enabled to trace each 

 effect to the concurrence of causes in which it originated, and 

 ascertain the conditions of its recurrence the circumstances 

 in which it may be expected again to occur. The conditions 

 of a phenomenon which arises from a composition of causes, 

 may be investigated either deductively or experimentally. 



The case, it is evident, is naturally susceptible of the 

 deductive mode of investigation. The law of an effect of this 

 description is a result of the laws of the separate causes on 

 the combination of which it depends, and is therefore in 

 itself capable of being deduced from these laws. This is 

 called the method a priori. The other, or a posteriori method, 

 professes to proceed according to the canons of experimental 

 inquiry. Considering the -whole assemblage of concurrent 

 causes which produced the phenomenon, as one single cause, 

 it attempts to ascertain the cause in the ordinary manner, by a 

 comparison of instances. This second method subdivides 

 itself into two different varieties. If it merely collates 

 instances of the effect, it is a method of pure observation. If 

 it operates upon the causes, and tries different combinations of 

 them, in hopes of ultimately hitting the precise combination 

 which will produce the given total effect, it is a method of 

 experiment. 



In order more completely to clear up the nature of each of 

 these three methods, and determine which of them deserves the 

 preference, it will be expedient (conformably to a favourite 

 maxirn of Lord Chancellor Eldon, to which, though it has 

 often incurred philosophical ridicule, a deeper philosophy will 

 not refuse its sanction) to " clothe them in circumstances." 



* Essays on some Unsettled Questions of Political Economy, Essay V. 



82 2 



