150 Mr WHEWELL, ON THE NATURE OF THE TRUTH 



men did at first suppose the laws of motion to be different from 

 what they are now proved to be. This would have been impossible 

 if the negation of these laws had involved a contradiction of self-evi- 

 dent principles, and consequently had been not only false but incon- 

 ceivable. These laws, therefore, cannot be necessary ; and can be duly 

 established in no other way than by a reference to experience. 



On the other hand, those who deduce their mechanical principles 

 without any express reference to experiment, may urge, on their side, 

 that, by the confession even of their adversaries, the laws of motion 

 are proved to be true beyond the limits of experience ; — that they are 

 assumed to be true of any new kind of motion when first detected, as 

 well as of those already examined; — and that it is inexplicable how 

 such truths should be established empirically. They may add that the 

 consequences of these laws are allowed to hold with the most complete 

 and absolute universality; for instance, the proposition that "the quan- 

 tity of motion in the world in a given direction cannot be either 

 increased or diminished," is conceived to be rigorously exact; and to 

 have a degree and kind of certainty beyond and above all mere facts 

 of experience ; what other kind of truth than necessary truth this 

 can be, it is difficult to say. And if the conclusions be necessarily 

 true, the principles must be so too. 



This apparent contradiction therefore, that a law should be neces- 

 sarily true and yet the contrary of it conceivable, is what I have now 

 to endeavour to explain ; and this I must do by pointing out what 

 appear to me the true grounds of the laws of motion. 



2. The science of Mechanics is concerned about motions as deter- 

 mined by their causes, namely, forces ; the nature and extent of the 

 truth of the first principles of this science must therefore depend upon 

 the way in which we can and do reason concerning causes. In what 

 manner we obtain the conception of cause, is a question for the meta- 

 physician, and has been the subject of much discussion. But the general 

 principle which governs our mode of viewing occurrences with reference 

 to this conception, so far as our present subject is concerned, does not 

 appear to be disturbed by any of the arguments which have been 



