382 INDUCTION. 



of mendacity from the character of the witness being supposed the 

 same in both cases) mendacity was 999 times less likely to have pro- 

 duced the particular assertion made, and is therefore 999 times less 

 likely to have existed, in the former case than in the latter. 



The error of this argument seems to be the same which we pointed 

 out in a former chapter,* that of applying a theorem, only true of the 

 degrees of probability of causes, to the probability of what are neither 

 causes nor indications of causes, nor in any other way specially con- 

 nected with the effect. The point in question is, the comparative 

 probability of two suppositions, that the witness lies, and that he speaks 

 truth. But these are not two possible causes of the given effect (the 

 witness's assertion) ; they are merely two possible qualities of it. The 

 truth of the assertion is, indeed, on the supposition of veracity, the 

 cause of its being made ; but the falsity of it is not, on any supposition, 

 a cause of its being made. It is not incompatible with the dishonesty 

 of the witness that he should have spoken the truth : the difl'erence be- 

 tween the two suppositions of honesty and dishonesty is, that on the one 

 he would certainly speak the truth, while on the other he was just equal- 

 ly likely to speak that or anything else. If the falsity of the proposition 

 were a real cause for his asserting it, and there were no possible mode 

 of accounting for a false assertion but by supposing that it is made pre- 

 cisely because of its falsity, I do not see how Laplace's argument could 

 be resisted. The case where there arc 999 possible false assertions, 

 and that in which there is but one, would then present a vast differ- 

 ence in the probability that the assertion actually made proceeded trom 

 falsity ; because in the one case a mendacious witness was sure to as- 

 sert the one false fact, in the other there would be an equal chance of 

 his asserting any one of the 999. But as it is, the falsity was a mere 

 accident of the assertion, not the cause of it ; and even on the suppo- 

 sition of dishonesty, the statement is as likely to be true as false, while 

 on the supposition of honesty it is certain to be true. The assertion, 

 therefore, is credible. 



With these remarks we shall close the discussion of the Grounds of 

 Disbelief; and along with it, such exposition as our space admitted, 

 and as the wrriter had it in his power to furnish, of the Logic of Induc- 

 tion. 



* Supra, p. 324. 



