FALLACIES OF GENERALIZATION. 367 



perty, but resembles the first in a property A, not known to 

 be connected with B ; and the conclusion to which the analogy 

 points, is that this object has the property B also. As, for 

 example, that the planets are inhabited, because the earth is 

 so. The planets resemble the earth in describing elliptical 

 orbits round the sun, in being attracted by it and by one an 

 other, in being nearly spherical, revolving on their axes, &c.; 

 but it is not known that any of these properties, or all of 

 them together, are the conditions on which the possession of 

 inhabitants is dependent, or are marks of those conditions. 

 Nevertheless, so long as we do not know 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 the slightest reason to suppose any 

 real connexion between the two properties A and B, the argu 

 ment is no longer one of analogy. If it had been ascertained 

 (I purposely put an absurd supposition) that there was a con 

 nexion by causation between the fact of revolving on an axis 

 and the existence of animated 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 causation, and not from 

 the analogy of the earth. 



The name analogy, however, is sometimes employed 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 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 occa- 



