46 INDUCTION. 



mode of coexistence of those causes, or of the primi- 

 tive natural agents on which the causes ultimately 

 depend. The proposition that coal beds rest upon 

 certain descriptions of strata exclusively, though true 

 on the earth so far as our observation has reached, 

 cannot be extended to the moon or the other planets, 

 supposing coal to exist there ; because we cannot be 

 assured that the original constitution of any other 

 planet was such as to produce the different depositions 

 in the same order as in our globe. The derivative 

 law in this case depends not solely upon laws but 

 upon a collocation ; and collocations cannot be reduced 

 to any law. 



Now it is the very nature of a derivative law which 

 has not yet been resolved into its elements, in other 

 words, an empirical law, that we do not know whe- 

 ther it results from the different effects of one cause 

 or from effects of different causes. We cannot tell 

 whether it depends wholly upon laws, or partly upon 

 laws and partly upon a collocation. If it depends 

 upon a collocation, it will be true in all the cases in 

 which that particular collocation exists. But since 

 we are entirely ignorant, in case of its depending upon 

 a collocation, what the collocation is, we are not safe 

 in extending the law beyond the limits of time and 

 place in which we have actual experience of its truth. 

 Since within those limits the law has always been 

 found true, we have evidence that the collocations, what- 

 ever they are, upon which it depends, do really exist 

 within those limits. But knowing of no rule or prin- 

 ciple to which the collocations themselves conform, 

 we cannot conclude that because a collocation is 

 proved to exist within certain limits of place or time, 

 it will exist beyond those limits. Empirical laws, 

 therefore, can only be held true within the limits of 



