CALCULATION OF CHANCES. 75 



to things of which we are completely ignorant, than 

 to things of which we have partial knowledge. Where 

 we have some experience of the occurrence of each of 

 the conflicting possibilities, it may often be difficult, 

 according to the prescriptions of the theory, to reduce 

 those possibilities to a definite number of cases, all 

 equally probable ; but when the case is out of the reach 

 of all experience, so that we have no difficulty in 

 being " equally undecided" respecting the possibilities, 

 there is nothing to make us halt or waver in apply- 

 ing the theory. If the question be whether the inha- 

 bitants of Saturn have red hair, we need only know 

 the number of the prismatic colours, and of their more 

 marked compounds, and we can at once assign the 

 fraction corresponding to the probability! It is evi- 

 dent that probability, in any sense in which it can 

 operate upon our belief or conduct, has nothing to do 

 with such chimerical evaluations, and that entire sus- 

 pension of judgment, where we have no evidence, is 

 the only course befitting a rational being. To entitle 

 us to affirm anything positive about uncertain facts, 

 whether it be that one supposition is more probable than 

 another, or only that it is equally probable, we must 

 have the testimony of experience, that, taking the 

 whole of some class of cases, the one guess will be 

 oftener right, or as often right as the other. The 

 estimation, in short,of chances, like that of certainties, 

 is only rational when grounded upon a complete 

 induction by observation or experiment*. 



* Confusion is sometimes introduced into this subject by not 

 adverting to the distinction between the chances that a given event 

 will happen, and the chances that a guess, not yet made, respecting 

 its occurrence, will be right. Supposing that I have no more 

 reason to expect one event than another, it is (from experience of 



