188 NAMES AND PROPOSITIONS. 



connotes. This gives rise to two sorts of imperfect, 

 or unscientific definitions ; namely, Essential but incom- 

 plete Definitions, and Accidental Definitions, or Descrip- 

 tions. In the former, a connotative name is defined by 

 a part only of its connotation ; in the latter, by some- 

 thing which forms no part of the connotation at all. 



An example of the first kind of imperfect defini- 

 tions is the following: Man is a rational animal. It 

 is impossible to consider this as a complete defini- 

 tion of the word Man, since (as before remarked) if 

 we adhered to it we should be obliged to call the 

 Houyhnhms men ; but as there happen to be no 

 Houyhnhms, 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 predi- 

 cable. 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 

 enumerated attributes, possess also those which are 

 omitted ; so that the field of predication which the 

 word covers, and the employment 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 differen- 

 tiam. Differentia being seldom taken to mean the 

 whole of the peculiarities constitutive 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 



