DEMONSTRATION, AND NECESSARY TRUTHS. 277 



it is self-evident, and does not need the evidence of experience 

 at all. 



This I take to be the real and sufficient explanation of the 

 paradoxical truth, on which so much stress is laid by Dr. 

 Whewell, that a scientifically cultivated mind is actually, in 

 virtue of that cultivation, unable to conceive suppositions 

 which a common man conceives without the smallest diffi- 

 culty. For there is nothing inconceivable in the suppositions 

 themselves ; the impossibility is in combining them with facts 

 inconsistent with them, as part of the same mental picture ; 

 an obstacle of course only felt by those who know the facts, 

 and are able to perceive the inconsistency. As far as the sup- 

 positions themselves are concerned, in the case of many of 

 Dr. Whewell's necessary truths the negative of the axiom is, 

 and probably will be as long as the human race lasts, as easily 

 conceivable as the affirmative. There is no axiom (for ex- 

 ample) to which Dr. Whewell ascribes a more thorough cha- 

 racter of necessity and self-evidence, than that of the indestruc- 

 tibility of matter. That this is a true law of nature I fully 

 admit ; but I imagine there is no human being to whom the 

 opposite supposition is inconceivable who has any difficulty in 

 imagining a portion of matter annihilated : inasmuch as its 

 apparent annihilation, in no respect distinguishable from real 

 by our unassisted senses, takes place every time that water 

 dries up, or fuel is consumed. Again, the law that bodies 

 combine chemically in definite proportions is undeniably true ; 

 but few besides Dr. Whewell have reached the point which he 

 seems personally to have arrived at, (though he only dares 

 prophesy similar success to the multitude after the lapse of 

 generations,) that of being unable to conceive a world in which 

 the elements are ready to combine with one another " indiffe- 

 rently in any quantity ;" nor is it likely that we shall ever rise 

 to this sublime height of inability, so long as all the mechanical 

 mixtures in our planet, whether solid, liquid, or aeriform, ex- 

 hibit to our daily observation the very phenomenon declared to 

 be inconceivable. 



According to Dr. Whewell, these and similar laws of nature 

 cannot be drawn from experience, inasmuch as they are, on 



