98 INDUCTION. 



one; therefore it is true of the other. But we have 

 here nothing by which to discriminate analogy from 

 induction, since this type will serve for all reasoning 

 from experience. In the most rigid induction, equally 

 with the faintest analogy, we conclude because A 

 resembles B in one or more properties, that it does so 

 in a certain other property. The difference is, that 

 in the case of a real induction it has been previously 

 shown, by due comparison of instances, that there is an 

 invariable conjunction between the former property or 

 properties and the latter property : but in what is called 

 analogical reasoning, no such conjunction has been 

 made out. There have been no opportunities of putting 

 in practice the Method of Difference, or even the 

 Method of Agreement; but we 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 properties (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 

 properties 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 

 dependent upon some property of A, but we know not 

 upon which. We cannot point out any of the pro- 

 perties of A, which is the cause of m, or united with 

 it by any law. After rejecting all which we know to 



