140 Measurement of Belief. [CHAP. vi. 



Here then a problem proposes itself. If popular opinion, 

 as illustrated in common language, be correct, and very 

 considerable weight must of course be attributed to it, there 

 does exist something which we call partial belief in refer 

 ence to any proposition of the numerical kind described 

 above. Now what we want to do is to find some test or 

 justification of this belief, to obtain in fact some intelligible 

 answer to the question, Is it correct ? We shall find incident 

 ally that the answer to this question will throw a good deal 

 of light upon another question nearly as important arid far 

 more intricate, viz. What is the meaning of this partial belief? 



18. We shall find it advisable to commence by ascer 

 taining how such enquiries as the above would be answered 

 in the case of ordinary full belief. Such a step would not 

 offer the slightest difficulty. Suppose, to take a simple 

 example, that we have obtained the following proposition, 

 whether by induction, or by the rules of ordinary deductive 

 logic, does not matter for our present purpose, that a certain 

 mixture of oxygen and hydrogen is explosive. Here we have 

 an inference, and consequent belief of a proposition. Now 

 suppose there were any enquiry as to whether our belief 

 were correct, what should we do? The simplest way of 

 settling the matter would be to find out by a distinct appeal 

 to experience whether the proposition was true. Since we 

 are reasoning about things, the justification of the belief, that 

 is, the test of its correctness, would be most readily found in 

 the truth of the proposition. If by any process of inference 

 I have come to believe that a certain mixture will explode, I 

 consider my belief to be justified, that is to be correct, if 

 under proper circumstances the explosion always does occur ; 

 if it does not occur the belief was wronsr. 



o 



Such an answer, no doubt, goes but a little way, or rather 

 no way at all, towards explaining what is the nature of beliei 



