DEFINITION. 



89 



proceed to examine some opinions of 

 philosophers, and some popular con- 

 ceptions on the subject, which conflict 

 more or less with that idea. 



The only adequate definition of a 

 name is, as already remarked, one 

 which declares the facts, and the 

 whole of the facts, which the name 

 involves in its signification. But with 

 most persons the object of a definition 

 does not embrace so much ; they look 

 for nothing more, in a definition, than 

 a guide to the correct use of the term 

 — a protection against applying it in 

 a manner inconsistent with custom 

 and convention. Anjrthing, there- 

 fore, is to them a sufficient definition 

 of a term which will serve as a cor- 

 rect index to what the term denotes ; 

 though not embracing the whole, and 

 sometimes, perhaps, not even any 

 part, of what it connotes. This gives 

 rise to two sorts of imperfect or un- 

 scientific definition ; Essential but in- 

 complete Definitions, and Accidental 

 Definitions, or Descriptions. In the 

 former, a connotative name is defined 

 by a part only of its connotation ; in 

 the latter, by something which forms 

 no part of the connotation at all. 



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 com- 

 plete definition of the word Man, 

 since (as before remarked) if we ad- 

 hered 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. Tliough 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 attri- 

 butes possess also those which are 

 omitted ; so that the field of predica- 

 tion which the word covers, and the 

 employment of it which is conform- 

 able to usage, are as well indicated 



by the inadequate definition as by an 

 adequate one. Such definitions, how- 

 ever, are always liable to be over- 

 thrown 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 be- 

 ing seldom taken to mean the whole 

 of the peculiarities constitutive of 

 the species, but some one of those 

 peculiarities only, a complete defini- 

 tion would be per genus et diffh'entias, 

 rather than differentiam. It would 

 include, with the name of the superior 

 genus, not merely some attribute 

 which distinguishes the species in- 

 tended to be defined from all other 

 species of the same genus, but aU the 

 attributes implied in the name of the 

 species, which the name of the supe- 

 rior genus has not already implied. 

 The. assertion, however, that a defini- 

 tion must of necessity consist of a 

 genus and differentiae, is not tenable. 

 It was early remarked by logicians, 

 that the summum genus in any classi- 

 fication, 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 ulti- 

 mately composed. 



§ 4. Although the first kind of 

 imperfect definition, (which defines a 

 connotative term by a part only of 

 what it connotes, but a part sufficient 

 to mark out correctly the boundaries 

 of its denotation,) has been considered 

 by the ancients, and by logicians in 

 general, as a complete definition, it 

 has always been deemed necessary 

 that the attributes employed should 

 really form part of the connotation ; 

 for the rule was that the definition 

 must be drawn from the essence of 

 the class ; and this would not have 



