GROUND OF INDUCTION. 379 



conclusion has turned out erroneous. The expe- 

 rience, however, on which the conclusion rested was 

 genuine. From the earliest records, the testimony of 

 all the inhabitants of the known world was unanimous 

 on the point. The uniform experience, therefore, of 

 the inhabitants of the known world, agreeing in a 

 common result, without one known instance of devia- 

 tion from that result, is not always sufficient to establish 

 a general conclusion. 



But let us now turn to an instance apparently not 

 very dissimilar to this. Mankind were wrong, it 

 seems, in concluding that all swans were white : are 

 we also wrong, when we conclude that all men's heads 

 grow above their shoulders, and never below, in spite 

 of the conflicting testimony of the naturalist Pliny ? 

 As there were black swans, although civilized men 

 had existed for three thousand years on the earth 

 without meeting with them, may there not also be 

 " men whose heads do grow beneath their shoulders," 

 notwithstanding a rather less perfect unanimity of 

 negative testimony from all observers? Most per- 

 sons would answer No ; it was more credible that a 

 bird should vary in its colour, than that man should 

 vary in the relative position of his principal organs. 

 And there is no doubt that in so saying they would be 

 right : but to say why they are right, would be impos- 

 sible, without entering, more deeply than is usually 

 done, into the true theory of Induction. 



Again, there are cases in which we reckon with 

 the most unfailing confidence upon uniformity, and 

 other cases in which we do not count upon it at all. In 

 some, we feel complete assurance that the future will 

 resemble the past, the unknown be precisely similar to 

 the known. In others, however invariable may be 

 the result obtained from the instances which we have 



