270 REASONING. 



the conception of two straight lines inclosing a space ? Nor 

 is even this all. I have already called attention to the pecu 

 liar property of our impressions of form, that the ideas or 

 mental images exactly resemhle their prototypes, and ade 

 quately represent them for the purposes of scientific observa 

 tion. From this, and from the intuitive character of the 

 observation, which in this case reduces itself to simple inspec 

 tion, we cannot so much as call up in our imagination two 

 straight lines, in order to attempt to conceive them inclosing 

 a space, without by that very act repeating the scientific 

 experiment which establishes the contrary. Will it really be 

 contended that the inconceivableness of the thing, in such cir 

 cumstances, proves anything against the experimental origin 

 of the conviction ? Is it not clear that in whichever mode our 

 belief in the proposition may have originated, the impossibility 

 of our conceiving the negative of it must, on either hypothesis, 

 be the same ? As, then, Dr. Whewell exhorts those who have 

 any difficulty in recognising the distinction held by him between 

 necessary and contingent truths, to study geometry, a condi 

 tion which I can assure him I have conscientiously fulfilled, 

 I, in return, with equal confidence, exhort those who agree 

 with him, to study the general laws of association ; being con 

 vinced that nothing more is requisite than a moderate familiarity 

 with those laws, to dispel the illusion which ascribes a peculiar 

 necessity to our earliest inductions from experience, and mea 

 sures the possibility of things in themselves, by the human 

 capacity of conceiving them. 



1 hope to be pardoned for adding, that Dr. Whewell him 

 self has both confirmed by his testimony the effect of habitual 

 association in giving to an experimental truth the appearance 

 of a necessary one, and afforded a striking instance of that 

 remarkable law in his own person. In his Philosophy of the 

 Inductive Sciences he continually asserts, that propositions 

 which not only are not self-evident, but which we know to 

 have been discovered gradually, and by great efforts of genius 

 and patience, have, when once established, appeared so self- 

 evident that, but for historical proof, it would have been impos 

 sible to conceive that they had not been recognised from the 



