INTERMIXTURE OF EFFECTS. 259 



that all general truths have exceptions ; and much unmerited distrust 

 has thence accrued to the conclusions of philosophy, when they have 

 been submitted to. the judgment of persons who wei-.e not philosophers. 

 The rough generalizations suggested by common observation usually 

 have exceptions ; but the principles of science, or in other words, the 

 laws of causation, have not. " What is thought to be a,n exception to 

 a princi})le," (tii quote words used on a difterent occasion,) " is always 

 some other and distuict principle cutting into the former ; some other 

 force which impinges against the first force, and deflects it from its 

 direction. Therd are not a law and an exception to that l,aw, the Itivv 

 acting in ninety-nine cases and the exception in one.. There are two 

 laws, each possibly acting in the whole hundi'cd cases, ai\d bringing 

 about a common effect by their conjunct oj)ei'ation. If tl>c foixc which, 

 being the less conspicuous of the two, is called the dhturhing force, 

 prevails sufficiently over the other force in some one case, to constitute 

 that case what is commonly called an exception, the same disturbing 

 force prqbably acts as a modifying cause in many other cases which no 

 one will call exceptions. . 



" Thus if it wei'e stated to be a law of nature that all heavy bodies , 

 fall to the ground, it wx)uld probably be said "that the resistance of the 

 atmosphere, which prevents a balloon from falling, constitutes the 

 balloon an exception to that pretended law of nature. But the real 

 law is, that all heavy bodies tend to fall ; and to this there is no excep- 

 tion, not even the sun and moon ; for even they, as every astronomer 

 knows, tend towards the earth, with a force exactly equal to that with 

 which the earth tends towards them. The resistance of the atmosphere 

 might, in the particular case of the balloon, from a misapprehension of 

 what the law of gravita,tion is", be said to prevail over the law ; but its 

 disturbing effect is quite as real in evej-y other case, since, though it 

 does not prevent, it retards th6 fall of all bodies whatever. The rule, 

 and the so-called exception, do not divide the cases between them ; 

 each of thern is a comprehensive rule extending to all cases. To call 

 one of these c(»ncurrent principles an exception to the other, is super- 

 ficial, and contrary to the correct principles 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 docs not exist another cause preponderating 

 over it." 



§ G. We have now to consider according to what method these 

 complex effects, compounded of the effects of many causes, are to be 

 studied ; how we are enabled to trace each eflect 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 \vhich arises from a com- 

 position of causes, may be investigated '. either deductively or experi- 

 mentally. 



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 

 vosteriori method, professes to proceed according to the canons of 



