SECT. 16.] Measurement of Belief. 137 



been contrived that there shall be no appreciable difference 

 between the alternatives, by which to decide in favour of 

 one or other, and we accordingly feel no confidence in the 

 particular result. Having to decide, however, we decide ac 

 cording to the precedent of similar cases which have occurred 

 before. To stand still and wait for better information is 

 certain death, and we therefore appeal to and employ the 

 only rule we know of; or rather we feel, or endeavour to 

 feel, as we have felt before when acting in the presence of 

 alternatives as nearly balanced as possible. But I can 

 neither perceive in my own case, nor feel convinced in that 

 of others, that this appeal, in a case which cannot be re 

 peated 1 , to a rule acted on and justified in cases which can be 

 and are repeated, at all forces us to admit that our state of 

 mind is the same in each case. 



16. This example serves to bring out very clearly a point 

 which has been already mentioned, and which will have to be 

 insisted upon again, viz. that all which Probability discusses 

 is the statistical frequency of events, or, if we prefer so to 

 put it, the quantity of belief with which any one of these 

 events should be individually regarded, but leaves all the 

 subsequent conduct dependent upon that frequency, or that 

 belief, to the choice of the agents. Suppose there are two 

 travellers in the predicament in question : shall they keep 

 together, or separate in opposite directions ? In either case 

 alike the chance of safety to each is the same, viz. one-half, 

 but clearly their circumstances must decide which course it 

 is preferable to adopt. If they are husband and wife, they will 

 probably prefer to remain together ; if they are sole deposi 

 taries of an important state secret, they may decide to part. 

 In other words, we have to select here between the two alter 

 natives of the certainty of a single loss, and the even chance 



1 Except indeed on the principles indicated further on in 24, 25. 



