88 INDUCTION. 



conclude (and that is all which the argument of analogy 

 amounts to) that a fact m, known to be true of A, is more 

 likely to be true of B if B agrees with A in some of its pro 

 perties (even though no connexion is known to exist between 

 m and those properties), than if no resemblance at all could be 

 traced between B and any other thing known to possess the 

 attribute m. 



To this argument it is of course requisite, that the pro 

 perties common to A with B shall be merely not known to be 

 connected with m ; they must not be properties known to be 

 unconnected with it. If, either by processes of elimination, 

 or by deduction from previous knowledge of the laws of the 

 properties in question, it can be concluded that they have 

 nothing to do with m, the argument of analogy is put out of 

 court. The supposition must be that m is an effect really de 

 pendent on some property of A, but we know not on which. 

 We cannot point out any of the properties of A, which is the 

 cause of m, or united with it by any law. After rejecting all 

 which we know to have nothing to do with it, there remain 

 several between which we are unable to decide : of which 

 remaining properties, B possesses one or more. This ac 

 cordingly, we consider as affording grounds, of more or less 

 strength, for concluding by analogy that B possesses the 

 attribute m. 



There can be no doubt that every such resemblance which 

 can be pointed out between B and A, affords some degree of 

 probability, beyond what would otherwise exist, in favour of 

 the conclusion drawn from it. If B resembled A in all its 

 ultimate properties, its possessing the attribute m would be a 

 certainty, not a probability : and every resemblance which can 

 be shown to exist between them, places it by so much the 

 nearer to that point. If the resemblance be in an ultimate 

 property, there will be resemblance in all the derivative pro 

 perties dependent on that ultimate property, and of these m 

 may be one. If the resemblance be in a derivative property, 

 there is reason to expect resemblance in the ultimate property 

 on which it depends, and in the other derivative properties 

 dependent on the same ultimate property. Every resemblance 



