356 INDUCTION. 



tions, and consider why it is that, with exactly the same 

 amount of evidence, hoth 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 be believed than the other ? Apparently because 

 there is less constancy in the colours of animals, than in the 

 general structure of their anatomy. But how do we know 

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

 need experience to inform us, in what degree, and in what 

 cases, or sort of cases, experience is to be relied on. Expe- 

 rience 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 experience its own test. Experience testifies, that 

 among the uniformities which it exhibits or seems to exhibit, 

 some are more to be relied on than others ; and uniformity, 

 therefore, may be presumed, from any given number of in- 

 stances, with a greater degree of assurance, in proportion as 

 the case belongs to a class in which the uniformities have 

 hitherto been found more uniform. 



This mode of correcting one generalization by means of 

 another, a narrower generalization by a wider, which common 

 sense suggests and adopts in practice, is the real type 

 of scientific Induction. All that art can do is but to give 

 accuracy and precision to this process, and adapt it to all 

 varieties of cases, without any essential alteration in its 

 principle. 



There are of course no means of applying such a test as 

 that above described, unless we already possess a general 

 knowledge of the prevalent character of the uniformities 

 existing throughout nature. The indispensable foundation, 

 therefore, of a scientific formula of induction, must be a 

 survey of the inductions to which mankind have been con- 

 ducted in unscientific practice; with the special purpose of 



