DEFINITION. 153 



An example of the first kind of imperfect definitions is the 

 following: Man is a rational animal. It is impossible to 

 consider this as a complete definition of the word Man, since 

 (as before remarked) if we adhered to it we should be obliged 

 to call the Houyhnhnms men ; but as there happen to be no 

 Houyhnhnms, this imperfect definition is sufficient to mark 

 out and distinguish from all other things, the objects at present 

 denoted by " man ;" all the beings actually known to exist, of 

 whom the name is predicable. Though the word is defined by 

 some only among the attributes which it connotes, not by all, 

 it happens that all known objects which possess the enume- 

 rated attributes, possess also those which are omitted ; so that 

 the field of predication which the word covers, and the employ- 

 ment of it which is conformable to usage, are as well indicated 

 by the inadequate definition as by an adequate one. Such 

 definitions, however, are always liable to be overthrown by the 

 discovery of new objects in nature. 



Definitions of this kind are what logicians have had in 

 view, when they laid down the rule, that the definition of a 

 species should be per genus et differentiam. Differentia being 

 seldom taken to mean the whole of the peculiarities constitu- 

 tive of the species, but some one of those peculiarities only, 

 a complete definition would be per genus et differentias, rather 

 than differentiam. It would include, with the name of the 

 superior genus, not merely some attribute which distinguishes 

 the species intended to be defined from all other species of the 

 same genus, but all the attributes implied in the name of the 

 species, which the name of the superior genus has not already 

 implied. The assertion, however, that a definition must of 

 necessity consist of a genus and differentiae, is not tenable. It 

 was early remarked by logicians, that the summum genus in 

 any classification, having no genus superior to itself, could not 

 be defined in this manner. Yet we have seen that all names, 

 except those of our elementary feelings, are susceptible of 

 definition in the strictest sense ; by setting forth in words the 

 constituent parts of the fact or phenomenon, of which the 

 connotation of every word is ultimately composed. 



