GROUND OF INDUCTION. 349 



which the logician must solve if he would establish a scientific 

 theory of Induction, let us compare a few cases of incorrect 

 inductions with others which are acknowledged to be legiti- 

 mate. Some, we know, which were believed for centuries to 

 be correct, were nevertheless incorrect. That all swans are 

 white, cannot have been a good induction, since the conclu- 

 sion has turned out erroneous. The experience, however, on 

 which the conclusion rested, was genuine. From the earliest 

 records, the testimony of the inhabitants of the known world 

 was unanimous on the point. The uniform experience, there- 

 fore, of the inhabitants of the known world, agreeing in a 

 common result, without one known instance of deviation 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 con- 

 cluding 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, though civi- 

 lized people 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," notwith- 

 standing a rather less perfect unanimity of negative testimony 

 from observers ? Most persons would answer No ; it was 

 more credible that a bird should vary in its colour, than that 

 men should vary in the relative position of their principal 

 organs. And there is no doubt that in so saying they would 

 be right : but to say why they are right, would be impossible, 

 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 have been observed, we draw from them no more than 



