108 NAMES AND PROPOSITIONS. 



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 hajipen 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 

 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 

 differ entiam. 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 Avould 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 de- 

 fined from all other species of the same genus, but all the attributes im- 

 plied 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 differentias, is not tenable. It Avas early- 

 remarked by logicians, that the summum genus in any classification, hav- 

 ing 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. 



§ 4. Although the first kind of imperfect definition (which defines a con- 

 notative 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 been the case 

 if it had been in any degree made up of attributes not connoted by the 

 name. The second kind of imperfect definition, therefore, in which the 

 name of a class is defined by any of its accidents — that is, by attributes 

 which are not included in its connotation — has been rejected from the rank 

 of genuine Definition by all logicians, and has been termed Description. 



This kind of imperfect definition, however, takes its rise from the same 

 cause as the other, namely, the willingness to accept as a definition any thing 

 which, whether it expounds the meaning of the name or not, enables us to 

 discriminate the things denoted by the name from all other things, and con- 

 sequently to employ the term in predication without deviating from estab- 

 lished usage. This purpose is duly answered by stating any (no matter 

 what) of the attributes which are common to the whole of the class, and 

 peculiar to it ; or any combination of attributes which happens to be pe- 

 culiar to it, though separately each of those attributes may be common to 



