THE DEDUCTIVE METHOD. 543 



By such raticionations from the separate laws of 

 the causes, we may, to a certain extent, succeed in 

 answering either of the following questions : Given a 

 certain combination of causes, what effect will follow? 

 and, What combination of causes, if it existed, would 

 produce a given effect? In the one case, we deter- 

 mine the effect to be expected in any complex circum- 

 stances of which the different elements are known : 

 in the other case we learn, according to what law 

 under what antecedent conditions a given complex 

 effect will recur. 



3. But (it may here be asked) are not the same 

 arguments by which the metfiods of direct observation 

 and experiment were set aside as illusory when 

 applied to the laws of complex phenomena, appli- 

 cable with equal force against the Method of De- 

 duction? When in every single instance a multitude, 

 often an unknown multitude, of agencies, are clashing 

 and combining, what security have we that in our 

 computation a priori we have taken all these into 

 our reckoning? How many must we not generally be 

 ignorant of? Among those which we know, how 

 probable that some have been overlooked ; and even 

 w r ere all included, how vain the pretence of summing 

 up the effects of many causes, unless we know accu- 

 rately the numerical law of each, a condition in most 

 cases not to be fulfilled; and even when fulfilled, to 

 make the calculation transcends, in any but very 

 simple cases, the utmost power of mathematical science 

 with its most modern improvements. 



These objections truly have much weight, and 

 would be altogether unanswerable, if there were no 

 test by which, when we employ the Deductive 

 Method, we might judge whether an error of any of 



