LAWS OF NATURE. 387 



knowledge pointed out limits to them, or shewed 

 their truth to be contingent upon some other circum- 

 stance not originally attended to. It will appear, I 

 think, from the subsequent part of our inquiry, that 

 there is no logical fallacy in this mode of proceed- 

 ing ; but we may see already that any other mode 

 is rigorously impracticable : since it is impossible to 

 frame any scientific method of induction, or test of the 

 correctness of inductions, unless upon the hypothesis 

 that some inductions of unquestionable certainty have 

 been already made. 



Let us revert, for instance, to one of our former 

 illustrations, and consider why it is that, with exactly 

 the same amount of evidence, both negative and 

 positive, we did not reject the assertion that there are 

 black swans, while we should refuse credence to any 

 testimony which asserted that there were men wearing 

 their heads underneath their shoulders. The first 

 assertion was more credible than the latter. But 

 why more credible ? So long as neither phenomenon 

 had been actually witnessed, what reason was there 

 for finding the one harder to believed than the other ? 

 Apparently, because there is less constancy in the 

 colours of animals, than in the general structure of 

 their internal anatomy. But how do we know this ? 

 Doubtless, from experience. It appears, then, that we 

 need experience to inform us, in what cases, or in 

 what sorts of cases, experience is to be relied upon. 

 Experience must be consulted in order to learn from 

 it under what circumstances arguments from it will 

 be valid. We have no ulterior test to which we 

 subject experience in general; but we make expe- 

 rience its own test. Experience testifies, that among 

 the uniformities which it exhibits or seems to exhibit, 

 some are more to be relied upon than others ; and 



2 c 2 



