DEMONSTRATION AND NECESSARY TRUTHS. 



157 



description than any which experience 

 can afford. 



Now I cannot but wonder that so 

 much stress should be laid on the cir- 

 cumstance of inconcnivableness, when 

 there is such ample experience to show 

 that our capacity or incapacity of con- 

 ceiving a thing has very little to do 

 with the possibility of the thing in 

 itself, but is in truth very much an 

 affair of accident, and depends on the 

 past history and habits of our own 

 minds. There is no more generally ac- 

 knowledged fact in human nature than 

 the extreme difficulty at first felt in 

 conceiving anything as possible which 

 is in contradiction to long-established 

 and familiar experience, or even to 

 old familiar habits of thought. And 

 this difficulty is a necessary result 

 of the fundamental laws of the human 

 mind. When we have often seen and 

 thought of two things together, and 

 have never in any one instance either 

 seen or thought of them separately, 

 there is by the primary law of asso- 

 ciation an increasing difficulty, which 

 may in the end become insuperable, 

 of conceiving the two things apart. 

 This is most of all conspicuous in un- 

 educated persons, who are in general 

 utterly unable to separate any two 

 ideas which have once become firmly 

 associated in their minds ; and if 

 persons of cultivated intellect have 

 any advantage on the point, it is only 

 because, having seen and heard and 

 read more, and being more accustomed 

 to exercise their imagination, they 

 have experienced their sensations and 

 thoughts in more varied combinations, 

 and have been prevented from form- 

 ing many of these inseparable asso- 

 ciations. But this advantage has 

 necessarily its limits. The most 

 practised intellect is not exempt from 

 the universal laws of our conceptive 

 faculty. If daily habit presents to 

 any one for a long period two facts 

 in combination, and if he is not led 

 during that period either by accident 

 or by his voluntary mental operations 

 to think of them apart, he will pro- 

 bably in time become incapable of 



doing so even by the strongest effort ; 

 and the supposition that the two 

 facts can be separated in nature will 

 at last present itself to his mind with 

 all the characters of an inconceivable 

 phenomenon.* There are remarkable 

 instances of this in the history of 

 science : instances in which the most 

 instructed men rejected as impossible, 

 because inconceivable, things which 

 their posterity, by earlier practice 

 and longer perseverance in the at- 

 tempt, found it quite easy to con- 

 ceive, and which everybody now 

 knows to be true. There was a time 

 when men of the most cultivated 

 intellects, and the most emancipated 

 from the dominion of early prejudice, 

 could not credit the existence of 

 antipodes ; were unable to conceive, 

 in opposition to old association, the 

 force of gravity acting upwards in- 

 stead of downwards. The Cartesians 

 long rejected the Newtonian doctrine 

 of the gravitation of all bodies to- 

 wards one another, on the faith of a 

 general proposition, the reverse of 

 which seemed to them to be incon- 

 ceivable — the proposition that a body 

 cannot act where it is not. All the 

 cumbrous machinery of imaginary 

 vortices, assumed without the smallest 

 particle of evidence, appeared to these 

 philosophers a more rational mode of 

 explaining the heavenly motions, than 

 one which involved what seemed to 

 them so great an absurdity.f And 



* " If all mankind had spoken one lan- 

 guage, we cannot doubt that there would 

 have been a powerful, perhaps a universal, 

 school of philosophers, who would have 

 believed in the inherent connection be- 

 tween names and things, who would have 

 taken the sound man to be the mode of 

 agitating the air which is essentially com- 

 municative of the ideas of rea-on, cookery, 

 bipedality, <fec." — De Morgan, Formal Logic, 

 p. 246. 



t It would be diflBcult to luime a man 

 more remarkable at once for the great- 

 ness and the wide range of his mentol ac- 

 complishments than Leibnitz. Yet this 

 eminent man gave as a reason for rejecting 

 Newton's scheme of the solar system, that 

 God could not make a body revolve round 

 a distant centre, unless either by some 

 impelling mechanism, or by miracle : — 

 "Tout oe qui n'eat pas explicable," says he 



