420 FALLACIES. 



what the conditions are, they may be connected by 

 some law of nature with those common properties; 

 and to the extent of that possibility the planets are 

 more likely to be inhabited, than if they did not 

 resemble the earth at all. This non-assignable and 

 generally small increase of probability, beyond what 

 would otherwise exist, is all the evidence which a 

 conclusion can derive from analogy. For if we have 

 any the slightest reason to suppose any real connexion 

 between the two properties A and B, the argument is 

 no longer one of analogy. If it had been ascertained 

 (I purposely put an absurd supposition) that there 

 was any connexion, by causation, between the fact 

 of revolving round an axis and the existence of ani- 

 mated beings, or if there were any reasonable ground 

 for even suspecting such a connexion, a probability 

 would arise of the existence of inhabitants in the 

 planets, which might be of any degree of strength, up 

 to a complete induction; but we should then infer the 

 fact from the ascertained or presumed law of causa- 

 tion, and not from the analogy of the earth. 



The name analogy, however, is sometimes em- 

 ployed by extension, to denote those arguments of 

 an inductive character, but not amounting to a real 

 induction, which are employed to strengthen the 

 argument drawn from a simple resemblance. Though 

 A, the property common to the two cases, cannot 

 be shown to be the cause or effect of B, the analogical 

 reasoner will endeavour, if he can, to show that there 

 is some less close degree of connexion between them ; 

 that A is one of a set of conditions from which, when 

 all united, B would result; or is an occasional effect 

 of some cause which has been known also to produce 

 B; and the like. Any of which things, if shown, 



