SECT. 34.] Measurement of Belief. 161 



side of the question. In the first place, as a mere specu 

 lative inquiry the quantity of our belief of any proposition 

 deserves notice. To study it at all deeply would be to tres 

 pass into the province of Psychology, but it is so intimately 

 connected with our own subject that we cannot avoid all 

 reference to it. We therefore discuss the laws under which 

 our expectation and surprise at isolated events increases or 

 diminishes, so as to account for these states of mind in any 

 individual instance, and, if necessary, to correct them when 

 they vary from their proper amount. 



But there is another more important reason than this. 

 It is quite true that when the subjects of our discussion in 

 any particular instance lie entirely within the province 

 of Probability, they may be treated without any reference 

 to our belief. We may or we may not employ this side of 

 the question according to our pleasure. If, for example, I 

 am asked whether it is more likely that A. B. will die this 

 year, than that it will rain to-morrow, I may calculate the 

 chance (which really is at bottom the same thing as my 

 belief) of each, find them respectively, one-sixth and one- 

 seventh, say, and therefore decide that my expectation of 

 the former is the greater, viz. that this is the more likely 

 event. In this case the process is precisely the same whether 

 we suppose our belief to be introduced or not ; our mental 

 state is, in fact, quite immaterial to the question. But, in 

 other cases, it may be different. Suppose that we are com 

 paring two things, of which one is wholly alien to Proba 

 bility, in the sense that it is hopeless to attempt to assign 

 any degree of numerical frequency to it, the only ground 

 they have in common may be the amount of belief to which 

 they are respectively entitled. We cannot compare the 

 frequency of their occurrence, for one may occur too seldom 

 to judge by, perhaps it may be unique. It has been already 



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