00 Origin, or Process of Causation of the Series. [CHAP. ill. 



made up of aggregates of small components, but they are 

 still best regarded as being by comparison simple and dis 

 tinct, for their component parts act mostly in groups col 

 lectively, appearing and disappearing together, so that they 

 possess the essential characteristics of unity. 



7. Now, broadly speaking, it appears to me that the 

 most suitable conditions for Probability are these : that the 

 important causes should be by comparison fixed and per 

 manent, and that the remaining ones should on the average 

 continue to act as often in one direction as in the other. 

 This they may do in two ways. In the first place we 

 may be able to predicate nothing more of them than the 

 mere fact that they act 1 as often in one direction as the 

 other; what we should then obtain would be merely the 

 simple statistical uniformity that is described in the first 

 chapter. But it may be the case, and in practice generally 

 is so more or less approximately, that these minor causes 

 act also in independence of one another. What we then 

 get is a group of uniformities such as was explained and 

 illustrated in the second chapter. Every possible combi 

 nation of these causes then occurring with a regular de 

 gree of frequency, we find one peculiar kind of uniformity 

 exhibited, not merely in the mere fact of excess and defect 

 (of whatever may be the variable quality in question), but 

 also in every particular amount of excess and defect. 

 Hence, in this case, we get what some writers term a 

 mean or type, instead of a simple average. For in 

 stance, suppose a man throwing a quoit at a mark. Here 

 our fixed causes are his strength, the weight of the quoit, 



1 As stated above, this is really that which we are called upon to ex- 

 little more than a re- statement, a plain in the concrete details pre- 

 stage further back, of the existence sented to us in experience, 

 of the same kind of uniformity as 



