350 INDUCTION. 



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 accuracy, we feel assured that the conclu- 

 sions he has arrived at will hold universally, though the 

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

 withhold our assent, waiting for a repetition of the experi- 

 ment ; or if we do, it is from a doubt whether the one experi- 

 ment 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 ex- 

 plored, 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 pro- 

 position ? Whoever can answer this question knows more of 

 the philosophy of logic than the wisest of the ancients, and has 

 solved the problem of induction. 



