318 THEORY OF THE SYSTEM. . 218. 



sent individuals, which, in so far as their forms are members 

 of the same series, differ only in these, and in none of their 

 other properties. Every combination occurring in nature 

 confirms, therefore, the above proposition ; and if we are 

 capable of deriving useful arguments from it, these will 

 be perfectly general, on account of the perfect generality 

 of the laws according to which combinations are formed 

 (. 130. 140.). 



The preceding observations are not limited to the series 

 of crystallisation ; but they extend to every natural-histo- 

 rical property, by the differences or gradations of which 

 series are produced. It applies, however, equally to any na- 

 tural-historical property whatever: their gradations may 

 produce series or not ; because those which give no series 

 at all, or at least not in every instance, may yet be consi- 

 dered as series of equal members. In the present inquiry 

 the series of forms have been chosen by preference, because 

 they allow of a mathematical mode of treatment, and there- 

 fore impart a full evidence to the arguments derived from 

 them. Together with the arguments, also, this evidence 

 is transferred to other series of properties treated in the 

 same manner. 



. 218. INDIVIDUALS BROUGHT UNDER THE IDEA 

 OF IDENTITY* 



Individuals, whose forms are members of a se- 

 ries, their remaining natural-historical properties 

 being entirely coincident, may be brought under 

 the idea of identity. 



It cannot be liable to any objection, that every indivi- 

 dual, not excepting those which appear in compound forms, 

 is identical with itself. But if in this combination we al- 

 low all the simple forms to disappear, except one, and con- 

 tinue this process with every simple form contained in the 

 combination ; we develope a scries of individuals, each of 

 which is exactly in the same relation to the idea of iden-. 



