SECT. 6.] Fallacies. 335 



vent, it is true, has happened, and we know what it is, and 

 therefore, we have not really any occasion to resort to the 

 rules of Probability; but we can nevertheless conceive our 

 selves as being in the position of a person who does not 

 know, and who has only Probability to appeal to. By calling 

 the chances 1679615 to 1 against the throw we then mean 

 to imply the fact, that inasmuch as such a throw occurs only 

 once in 1679616 times, our guess, were we to guess, would 

 be correct only once in the same number of times; provided, 

 that is, that it is a fair guisss, based simply on these statis 

 tical grounds. 



5. (2) But there is a second and very different con 

 ception sometimes introduced, especially when the event in 

 question is supposed to be known, not as above by the evi 

 dence of our experience, but by the report of a witness. We 

 may then mean by the chances against the event (as was 

 pointed out in Chapter xii.) not the proportional number of 

 times we should be right in guessing the event, but the 

 proportional number of times the witness will be right in 

 reporting it. The bases of our inference are here shifted 

 on to new ground. In the former case the statistics were 

 the throws and their respective frequency, now they are the 

 witnesses statements and their respective truthfulness. 



6. (3) But there is yet another meaning sometimes 

 intended to be conveyed when persons talk of the chances 

 against such an event as the throw in question. They may 

 mean not, Here is an event, how often should I have 

 guessed it ? nor, Here is a report, how often will it be 

 correct ? but something different from either, namely, Here 

 is an event, how often will it be found to be produced by 

 some one particular kind of cause ? 



When, for example, a man hears of dice giving the same 

 throw several times running, and speaks of this as very 



