SECT. 27.] Measurement of Belief. 151 



before, why it is that we are free from any necessity of as 

 suming the existence of causation, in the sense of necessary 

 invariable sequence, in the case of the events which compose 

 our series. Against such a view it might very plausibly be 

 urged, that we constantly talk of the probability of a single 

 event ; but how can this be done, it may reasonably be said, 

 if we once admit the possibility of that event occurring for 

 tuitously ? Take an instance from human life ; the average 

 duration of the lives of a batch of men aged thirty will be 

 about thirty-four years. We say therefore to any individual 

 of them, Your expectation of life is thirty-four years. But 

 how can this be said if we admit that the train of events 

 composing his life is liable to be destitute of all regular 

 sequence of cause and effect ? To this it may be replied 

 that the denial of causation enables us to say neither more 

 nor less than its assertion, in reference to the length of the 

 individual life, for of this we are ignorant in each case alike. 

 By assigning, as above, an expectation in reference to the 

 individual, we mean nothing more than to make a statement 

 about the average of his class. Whether there be causation 

 or not in these individual cases does not affect our knowledge 

 of the average, for this by supposition rests on independent 

 experience. The legitimate inferences are the same on either 

 hypothesis, and of equal value. The only difference is that 

 on the hypothesis of non-causation we have forced upon our 

 attention the impropriety of talking of the proper expecta 

 tion of the individual, owing to the fact that all knowledge of 

 its amount is formally impossible ; on the other hypothesis 

 the impropriety is overlooked from the fact of such know 

 ledge being only practically unattainable. As a matter of 

 fact the amount of our knowledge is the same in each case ; 

 it is a knowledge of the average, and of that only 1 . 



1 For a fuller discussion of this, see the Chapter on Causation. 



