SECT. 10.] Origin, or Process of Causation of the Series. 63 



irregularity disappear here, as elsewhere, if we kept our 

 tables open long enough, we shall find that the answer will 

 suggest another case in which the requisite conditions for 

 Probability are wanting. Such a reply would only be con 

 clusive upon the supposition that the ways and thoughts of 

 men are in the long run invariable, or if variable, subject to 

 periodic changes only. On the assumption of a steady pro 

 gress in society, either for the better or the worse, the argu 

 ment falls to the ground at once. From what we know of 

 the course of the world, these fearful pests of the past may 

 be considered as solitary events in our history, or at least 

 events which will not be repeated. No continued uniformity 

 would therefore be found in the deaths which they occasion, 

 though the registrar s books were kept open for a thousand 

 years. The reason here is probably to be sought in the 

 gradual alteration of those indefinitely numerous conditions 

 which we term collectively progress or civilization. Every 

 little circumstance of this kind has some bearing upon the 

 liability of any one to catch a disease. But when a kind of 

 slow and steady tide sets in, in consequence of which these 

 influences no longer remain at about the same average 

 strength, warring on about equal terms with hostile in 

 fluences, but on the contrary show a steady tendency to in 

 crease their power, the statistics will, with consequent steadi 

 ness and permanence, take the impress of such a change. 



10. Briefly then, if we were asked where the dis 

 tinctive characteristics of Probability are most prominently 

 to be found, and where they are most prominently absent, 

 we might say that (1) they prevail principally in the pro 

 perties of natural kinds, both in the ultimate and in the de 

 rivative or accidental properties. In all the characteristics of 

 natural species, in all they do and in all which happens to 

 them, so far as it depends upon their properties, we seldom 



