422 Credibility of Extraordinary Stories. [CHAP. xvu. 



them both. Let them now each report some extraordinary 

 lusus naturae or monstrosity which they profess to have seen. 

 Most persons, we may presume, would receive the statement 

 of the naturalist in this latter case almost as readily as in 

 the former: whereas when the same story came from the 

 unscientific observer it would be received with considerable 

 hesitation. Whence arises the difference? From the con 

 viction that the naturalist will be far more careful, and 

 therefore to the full as accurate, in matters of this kind as 

 in those of the most ordinary description, whereas with the 

 other man we feel by no means the same confidence. Even 

 if any one is not prepared to go this length, he will probably 

 admit that the difference of credit which he would attach to 

 the two kinds of story, respectively, when they came from 

 the naturalist, would be much less than what it would be 

 when they came from the other man. 



16. Whilst we are on this part of the subject, it must 

 be pointed out that there is considerable ambiguity and 

 consequent confusion about the use of the term an extraor 

 dinary story. Within the province of pure Probability it 

 ought to mean simply a story which asserts an unusual event. 

 At least this is the view which has been adopted and main 

 tained, it is hoped consistently, throughout this work. So 

 long as we adhere to this sense we know precisely what we 

 mean by the term. It has a purely objective reference; it 

 simply connotes a very low degree of relative statistical 

 frequency, actual or prospective. Out of a great number of 

 events we suppose a selection of some particular kind to be 

 contemplated, which occurs relatively very seldom, and this 

 is termed an unusual or extraordinary event. It follows, as 

 was abundantly shown in a former chapter, that owing to 

 the rarity of the event we are very little disposed to expect 

 its occurrence in any given case. Our guess about it, in case 



