204 EEASONING. 



its insufficiency, instead of being brought to light, is disguised, if instead of 

 sifting the experience itself, I appeal to a test which bears no relation to 

 the sufficiency of the experience, but, at the most, only to its familiarity. 

 Those remarks do not lose their force even if we believe, with Mr, Spencer, 

 that mental tendencies originally derived from experience impress them- 

 selves permanently on the cerebral structure and are transmitted by inher- 

 itance, so that modes of thinking which are acquired by the race become 

 innate and a priori in the individual, thus representing, in Mr. Spencer's 

 opinion, the experience of his j)rogenitors, in addition to his own. All that 

 would follow from this is, that a conviction might be really innate, i. e., prior 

 to individual experience, and yet not be true, since the inherited tendency 

 to accept it may have been originally the result of other causes than its 

 truth. 



Mr. Spencer would have a much stronger case, if he could really show 

 that the evidence of Reasoning rests on the Postulate, or, in other words, 

 that we believe that a conclusion follows from premises only because we 

 can not conceive it not to follow. But this statement seems to me to be 

 of the same kind as one I have previously commented on, viz., that I believe 

 I see light, because I can not, while the sensation remains, conceive that I 

 am looking into darkness. Both these statements seem to me incompatible 

 with the meaning (as very rightly limited by Mr. Spencer) of the verb to 

 conceive. To say that when I apprehend that A is B and that B is C, I 

 can not conceive that A is not C, is to my mind merely to say that I am 

 comjjelled to believe that A is C. If to conceive be taken in its proper 

 meaning, viz., to form a mental representation, I may be able to conceive A 

 as not being C. After assenting, with full understanding, to the Coperni- 

 can proof that it is the earth and not the sun that moves, I not only can 

 conceive, or represent to myself, sunset as a motion of the sun, but almost 

 every one finds this conception of sunset easier to form, than that which 

 they nevertheless know to be the true one. 



§ 5. Sir William Hamilton holds as I do, that inconceivability is no criteri- 

 on of impossibility. " There is no ground for inferring a certain fact to be 

 impossible, merely from our inability to conceive its ]30ssibility." " Things 

 there are which mai/, nay 77iust, be true, of which the understanding is 

 wholly unable to construe to itself the possibility."* Sir William Hamil- 

 ton is, however, a firm believer in the a priori character of many axioms, 

 and of the sciences deduced from them; and is so far from considering 

 those axioms to rest on the evidence of experience, that he declares certain 

 of them to be true even of Noumena — of the Unconditioned — of which it 

 is one of the principal aims of his philosophy to prove that the nature of 

 our faculties debars us from having any knowledge. The axioms to which 

 he attributes this exceptional emancipation from the limits which confine 

 all our other possibilities of knowledge ; the chinks through which, as he 

 represents, one ray of light finds its way to us from behind the curtain 

 which veils from us the mysterious world of Things in themselves — are 

 the two principles, which he terms, after the school-men, tlie Principle of 

 Contradiction, and the Principle of Excluded Middle : the first, that two 

 contradictory propositions can not both be true ; the second, that they can 

 not both be false. Armed with these logical weapons, we may boldly face 

 Things in themselves, and tender to them the double alternative, sure that 



* Discussions, etc., 2d ed., p. 624. 



