698 THE PRINCIPLES OF SCIENCE. [CHAP. 



what is not Sussex ; and so on. This is so far, however, 

 from being an absurd proceeding that it is requisite to 

 assure us that we have made an exhaustive enumeration of 

 the parts of England, 



The Five Predicates. 



As a rule it is highly desirable to consign to oblivion the 

 ancient logical names and expressions, which have infested 

 the science for many centuries past. If logic is ever to be 

 a useful and progressive science, logicians must distinguish 

 between logic and the history of logic. As in the case of 

 any other science it may be desirable to examine the course 

 of thought by which logic has, before or since the time of 

 Aristotle, been brought to its present state ; the history of a 

 science is always instructive as giving instances of the 

 mode in which discoveries take place. But at the same 

 time we ought carefully to disencumber the statement of 

 the science itself of all names and other vestiges of antiquity 

 which are not actually useful at the present day. 



Among the ancient expressions which may well be 

 excepted from such considerations and retained in use, are 

 the " Five Words " or " Five Predicables " which were 

 described by Porphyry in his introduction to Aristotle's 

 Organum. Two of them, Genus and Species, are the most 

 venerable names in philosophy, having probably been first 

 employed in their present logical meanings by Socrates. 

 In the present day it requires some mental effort, as 

 remarked by Grote, to see anything important in the 

 invention of notions now so familiar as those of Genus and 

 Species. But in reality the introduction of such terms 

 showed the rise of the first germs of logic and scientific 

 method; it showed that men were beginning to analyse 

 their processes of thought. 



The Five Predicables are Genus, Species, Difference, 

 Property, and Accident, or in the original Greek, 76^09, 

 elSo?, 8<a$opa, tSiov, (rv^fte^rjKo^. Of these, Genus may 

 be taken to mean any class of objects whicli is regarded as 

 broken up into two minor classes, which form Species of it. 

 The genus is defined by a certain number of qualities or 

 circumstances which belong to all objects included in the 

 class, and which are sufficient to mark out these objects 



