DEMONSTRATION, AND NECESSARY TRUTHS. 181 



evidence of axioms. For what is that theory ? That the truth of axioms 

 can not have been learned from experience, because their falsity is incon- 

 ceivable. But Dr. Whewell himself says, that we are continually led, by 

 tlie natural progress of thought, to regard as inconceivable what our fore- 

 fathers not only conceived but believed, nay even (he might have added) 

 were unable to conceive the reverse of. He can not intend to justify this 

 mode of thought : he can not mean to say, that we can be right in regard- 

 ing as inconceivable what others have conceived, and as self-evident what 

 to others did not appear evident at all. After so complete an admis- 

 sion that inconceivableness is an accidental thing, not inherent in the phe- 

 nomenon itself, but dependent on the mental history of the person M'ho 

 tries to conceive it, how can he ever call u23on us to reject a proposition as 

 impossible on no other ground than its inconceivableness? Yet he not 

 only does so, but has unintentionally afforded some of the most remarkable 

 examples which can be cited of the very illusion which he has himself so 

 clearly pointed out. I select as specimens, his remarks on the evidence of 

 the three laws of motion, and of the atomic theory. 



With respect to the laws of motion, Dr. Whewell says : " ISTo one can 

 doubt that, in historical fact, these laws were collected from experience. 

 That such is the case, is no matter of conjecture. We know the time, the 

 persons, the circumstances, belonging to each step of each discovery."* 

 After this testimony, to adduce evidence of the fact would be superfluous. 

 And not only were these laws by no means intuitively evident, but some 

 of them Avere originally paradoxes. The first law was especially so. That 

 a body, once in motion, would continue forever to move in the same direc- 

 tion with undiminished velocity unless acted upon by some new force, was 

 a proposition which mankind found for a long time the greatest difticulty 

 in crediting. It stood opposed to apparent experience of the most familiar 

 kind, which taught that it was the nature of motion to abate gradually, 

 ;uid at last terminate of itself. Yet when once the contrary doctrine was 

 firmly established, mathematicians, as Dr. Whewell observes, speedily be- 

 gan to believe that laws, thus contradictory to first appearances, and which, 

 even after full proof had been obtained, it had required generations to ren- 

 der familiar to the minds of the scientific world, were under " a demonstra- 

 ble necessity, compelling them to be such as they are and no other ;" and 

 he himself, though not venturing "absolutely to pronounce" that oM these 

 laws " can be rigorously traced to an absolute necessity in the nature of 

 things,"! does actually so think of the law just mentioned ; of which he 

 says : " Though the discovery of the first law of motion was made, histor- 

 ically speaking, by means of experiment, we have now attained a point of 

 view in which we see that it might have been certainly known to be true, 

 independently of experience."! Can there be a more striking exemplifi- 

 cation than is here afforded, of the effect of association which we have de- 

 scribed ? Philosophers, for generations, have the most extraordinary diffi- 

 culty in putting certain ideas together; they at last succeed in doing so; 

 and after a sufficient repetition of the process, they first fancy a natural 

 bond between the ideas, then experience a growing difficulty, which at last, 

 by the continuation of the same progress, becomes an impossibility, of sev- 

 ering them from one another. If such be the progress of an experimental 

 conviction of which the date is of yesterday, and which is in opposition to 

 first appearances, how must it fare with those which are conformable to 



♦ History of Scientific Ideas, i,, 264. t Ibid., i., 263. X Ibid., 240. 



