10 On certain kinds of Groups or Series. [CHAP. i. 



enough to point out tolerably clearly the kind of things 

 with which we have to deal, but it is not sufficiently definite 

 for purposes of accurate thought. We must therefore at 

 tempt a somewhat closer analysis. 



There are certain phrases so commonly adopted as to 

 have become part of the technical vocabulary of the sub 

 ject, such as an event and the way in which it can 

 happen. Thus the act of throwing a penny would be called 

 an event, and the fact of its giving head or tail would be 

 called the way in which the event happened. If we were 

 discussing tables of mortality, the former term would de 

 note the mere fact of death, the latter the age at which 

 it occurred, or the way in which it was brought about, 

 or whatever else in it might be the particular circumstance 

 under discussion. This phraseology is very convenient, and 

 will often be made use of in this work, but without expla 

 nation it may lead to confusion. For in many cases the 

 way in which the event happens is of such great relative 

 importance, that according as it happens in one way or 

 another the event would have a different name ; in other 

 words, it would not in the two cases be nominally the same 

 event. The phrase therefore will have to be considerably 

 stretched before it will conveniently cover all the cases to 

 which we may have to apply it. If for instance we were 

 contemplating a series of human beings, male and female, 

 it would sound odd to call their humanity an event, and 

 their sex the way in which the event happened. 



If we recur however to any of the classes of objects 

 already referred to, we may see our path towards obtaining 

 a more accurate conception of what we want. It will easily 

 be seen that in every one of them there is a mixture of 

 similarity and dissimilarity; there is a series of events 

 which have a certain number of features or attributes in 



