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. 



I 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 



