194 The Rule of Succession. [CHAP. vin. 



that, so far as concerns that definition of Probability which 

 regards it as the science which discusses the degree and 

 modifications of our belief, the question at issue seems to be 

 simply this: Are the causes alluded to above in (II) capable 

 of being reduced to one simple coherent scheme, so that any 

 universal rules for the modification of assent can be obtained 

 from them ? If they are, strong grounds will have been 

 shown for classing them with (I), in other words, for con 

 sidering them as rules of probability. Even then they 

 would be rules practically of a very different kind, contin 

 gent instead of necessary (if one may use these terms with 

 out committing oneself to any philosophical system), but this 

 objection might perhaps be overruled by the greater simpli 

 city secured by classing them together. This view is, with 

 various modifications, generally adopted by writers on Pro 

 bability, or at least, as I understand the matter, implied by 

 their methods of definition and treatment. Or, on the other 

 hand, must these causes be regarded as a vast system, one 

 might almost say a chaos, of perfectly distinct agencies; 

 which may indeed be classified and arranged to some extent, 

 but from which we can never hope to obtain any rules of 

 perfect generality which shall not be subject to constant 

 exception ? If so, but one course is left ; to exclude them 

 all alike from Probability. In other words, we must assume 

 the general proposition, viz. that which has been described 

 throughout as our starting-point, to be given to us ; it may 

 be obtained by any of the numerous rules furnished by 

 Induction, or it may be inferred deductively, or given by our 

 own observation; its value may be diminished by its depend 

 ing upon the testimony of witnesses, or its being recalled by 

 our own memory. Its real value may be influenced by 

 these causes or any combinations of them ; but all these are 

 preliminary questions with which we have nothing directly 



