380 INDUCTION. 



observed, we draw from them no more than a very 

 feeble presumption that the like result will hold in 

 all other cases. That a straight line is the shortest 

 distance between two points, we do not doubt to be 

 true even in the region of the fixed stars. When a 

 chemist announces the existence and properties of a 

 newly-discovered substance, if we confide in his accu- 

 racy, we feel assured that the conclusions he has 

 arrived at will hold universally, although the induc- 

 tion be founded but on a single instance. We do not 

 withhold our assent, waiting for a repetition of the 

 experiment; or if we do, it is from a doubt whether 

 the one experiment was properly made, not whether 

 if properly made it would be conclusive. Here, then, 

 is a general law of nature, inferred without hesitation 

 from a single instance ; an universal proposition from 

 a singular one. Now mark another case, and contrast 

 it with this. Not all the instances which have been 

 observed since the beginning of the world, in support 

 of the general proposition that all crows are black, 

 would be deemed a sufficient presumption of the truth 

 of the proposition, to outweigh the testimony of one 

 unexceptionable witness who should affirm that in 

 some region of the earth not fully explored, he had 

 caught and examined a crow, and had found it to be 

 grey. 



Why is a single instance, in some cases, sufficient 

 for a complete induction, while in others, myriads 

 of concurring instances, without a single exception 

 known or presumed, go such a very little way towards 

 establishing an universal proposition ? Whoever can 

 answer this question knows more of the philosophy 

 of logic than the wisest of the ancients, and has 

 solved the great problem of induction. 



