196 REASONING. 



ty men felt of conceiving sunset otherwise than as a motion of the sun, 

 represent any " net result " of experience in support of its being the sun 

 and not the earth that moves ? It is not experience that is represented, it 

 is only a superficial semblance of experience. The only thing proved with 

 regard to real experience, is the negative fact, that men have not had it 

 of the kind which would have made the inconceivable proposition conceiv- 

 able. 



Next : Even if it were true that inconceivableness represents the net re- 

 sult of all past experience, why should we stop at the representative when 

 we can get at the thing repi-esented ? If our incapacity to conceive the 

 negation of a given supposition is proof of its truth, because proving that 

 our experience has hitherto been uniform in its favor, the real evidence for 

 the supposition is not the inconceivableness, but the uniformity of experi- 

 ence. Now this, which is the substantial and only proof, is directly access- 

 ible. We are not obliged to presume it from an incidental consequence. 

 If all past experience is in favor of a belief, let this be stated, and the be- 

 lief openly rested on that ground : after which the question arises, what 

 that fact may be worth as evidence of its truth ? For uniformity of expe- 

 rience is evidence in very different degrees : in some cases it is strong evi- 

 dence, in others weak, in others it scarcely amounts to evidence at all. 

 That all metals sink in water, was a uniform experience, from the origin 

 of the human race to the discovery of potassium in the present century 

 by Sir Humphry Davy. That all swans are white, was a uniform experi- 

 ence down to the discovery of Australia. In the few cases in which uni- 

 formity of experience does amount to the strongest possible proof, as with 

 such propositions as these. Two straight lines can not inclose a space. Ev- 

 ery event has a cause, it is not because their negations are inconceivable, 

 which is not always the fact ; but because the experience, which has been 

 thus uniform, pervades all nature. It will be shown in the following Book 

 that none of the conclusions either of induction or of deduction can be 

 considered certain, except as far as their truth is shown to be inseparably 

 bound up with truths of this class. 



I maintain then, first, that uniformity of past experience is very far from 

 being universally a criterion of truth. But secondly, inconceivableness is 

 still further from being a test even of that test. Uniformity of contrary 

 experience is only one of many causes of inconceivability. Tradition 

 handed down from a period of more limited knowledge, is one of the com- 

 monest. The mere familiarity of one mode of production of a phenome- 

 non often suffices to make every other mode appear inconceivable. What- 

 ever connects two ideas by a strong association may, and continually does, 

 render their separation in thought impossible ; as Mr. Spencer, in other 

 parts of his speculations, frequently recognizes. It was not for want of ex- 

 perience that the Cartesians were unable to conceive that one body could 

 produce motion in another without contact. They had as much experience 

 of other modes of producing motion as they had of that mode. The plan- 

 ets had revolved, and heavy bodies had fallen, every hour of their lives. 

 But they fancied these phenomena to be produced by a hidden machinery 

 w^hich they did not see, because without it they were unable to conceive 

 what they did see. The inconceivableness, instead of representing their 

 experience, dominated and oveiTode their experience. Without dwelling 

 further on what I have termed the positive argument of Mr, Spencer in 

 support of his criterion of truth, I pass to his negative argument, on which 

 he lays more stress. 



