CAUSE AND EFFECT— PROBABILITY 139 



that it is well based. Belief in a fetish may be essential 

 to the welfare of a primitive tribe, and he who does not 

 believe in it may be exterminated ; yet this does not 

 demonstrate the rational character of the belief It is 

 right, therefore, that we should investigate whether our 

 conviction is well based, and to this point we shall devote 

 the remaining sections of this chapter. 



In concluding the present section we may resume the 

 results reached as follows : — 



In the order of perceptions (cause and effect) no in- 

 herent necessity can be demonstrated. 



In the uniformity with which sequences of perceptions 

 are repeated (the routine of perceptions) there is also no 

 inherent necessity, but it is a necessary condition for the 

 existence of thinking beings that there should be a 

 routine in perceptions. The necessity thus lies in the 

 nature of the thinking being and not in the perceptions 

 themselves ; thus it is conceivably a product of the per- 

 ceptive faculty. 



§ I 3 . — Probable and Provable 



Stanley Jevons in his discussion of the theory of 

 probability, which forms one of the most valuable and 

 interesting portions of his Principles of Science^ remarks 

 that the etymology of the word probable does not help us 

 to understand what probability is and where it exists : — 



" For, curiously enough, probable is ultimately the same 

 word as provable — a good instance of one word becoming 

 differentiated to two opposite meanings" (p. 197).^ 



Now we have seen that certainty belongs only to the 

 sphere of conceptions ; that inherent necessity has a 

 meaning in the mental field of logic, but that we cannot 

 postulate it in the universe of perceptions ; that the 

 " necessity of natural law " is really an unjustifiable 

 phrase. The word proof, therefore, used in the sense of a 



^ The source of both words must be sought, I think, in the mediaeval 

 Latin proba, a sample, test, or trial. 1\\\x% probare is used in the sense of 

 extracting a fact by torture, a.nd probabilis is that which by aid of the proba 

 has been attested and approved. 



