548 



CHAPTER XII. 

 OF THE EXPLANATION OF LAWS OF NATURE. 



1 . THE deductive operation by which we derive 

 the law of an effect from the laws of the causes, of 

 which the concurrence gives rise to it, may be under- 

 taken either for the purpose of discovering the law, or 

 of explaining a law already discovered. The word 

 explanation occurs so continually, and holds so im- 

 portant a place in philosophy, that a little time 

 spent in fixing the meaning of it will be profitably 

 employed. 



An individual fact is said to be explained, by 

 pointing out its cause, that is, by stating the law or 

 laws of causation, of which its production is an 

 instance. Thus, a conflagration is explained, when it 

 is proved to have arisen from a spark falling into the 

 midst of a heap of combustibles. And in a similar 

 manner, a law or uniformity in nature is said to be 

 explained, when another law or laws are pointed out, 

 of which that law itself is but a case, and from which 

 it could be deduced. 



2. There are three distinguishable sets of cir- 

 cumstances in which a law of causation may be 

 explained from, or, as it also is often expressed, 

 resolved into, other laws. 



The first is the case already so fully considered ; 

 an intermixture of laws, producing a joint effect equal 

 to the sum of the effects of the causes taken separately. 

 The law of the complex effect is explained, by being 

 resolved into the separate laws of the causes which 



