SECT. 3.] Credibility of Extraordinary Stories. 407 



ception, or event if we will so term it, had in fact passed 

 out of the category of guesses (on statistical grounds), into 

 that of assertions (most likely resting on some specific evi 

 dence), and would therefore be naturally regarded in a very 

 different light. 



2. But it may seem as if this principle would lead us 

 to somewhat startling conclusions. For, by transferring the 

 appeal from the frequency with which the event occurs to 

 the trustworthiness of the witness who makes the assertion, 

 is it not implied that the probability or improbability of an 

 assertion depends solely upon the veracity of the witness ? 

 If so, ought not any story whatever to be believed when 

 it is asserted by a truthful person ? 



In order to settle this question we must look a little 

 more closely into the circumstances under which such 

 testimony is commonly presented to us. As it is of course 

 necessary, for clearness of exposition, to take a numerical 

 example, let us suppose that a given statement is made by 

 a witness who, on the whole and in the long run, is right- 

 in what he says nine times out of ten 1 . Here then is an 

 average given to us, an average veracity that is, which 

 includes all the particular statements which the witness has 

 made or will make. 



3. Now it has been abundantly shown in a former 

 chapter (Ch. IX. 14 32) that the mere fact of a par- 



1 Beasons were given in the last another ; such a rough practical 



chapter against the propriety of ap- distinction will be quite sufficient 



plying the rules of Probability with for the purposes of this chapter, 



any strictness to such examples as For convenience, and to illustrate 



these. But although all approach the theory, the examples are best 



to numerical accuracy is unattain- stated in a numerical form, but it 



able, we do undoubtedly recognize is not intended thereby to imply 



in ordinary life a distinction between that any such accuracy is really 



the credibility of one witness and attainable in practice. 



