CLASSIFICATION AND THE PREDICABLES. 101 



The distinction, therefore, between Differentia, Proprium, and Accidens, 

 is not grounded in the nature of things, but in the connotation of names ; 

 and we must seek it there, if we wish to find what it is. 



From the fact that the genus includes the species, in other words (denotes 

 more than the species, or is predicable of a greater number of individuals, 

 it follows that the species must connote more than the genus. It must 

 connote all the attributes which the genus connotes, or there would be 

 nothing to prevent it from denoting individuals not included in the genus. 

 And it must connote something besides, otherwise it would include the 

 whole genus. Animal denotes all the individuals denoted by man, and 

 many more. Man, therefore, must connote all that animal connotes, other- 

 wise there might be men who are not animals ; and it must connote some- 

 thing more than animal connotes, otherwise all animals would be men. 

 This surplus of connotation — this which the species connotes over and 

 above the connotation of the genus — is the Differentia, or speci6c differ- 

 ence ; or, to state the same proposition in other words, the Differentia is 

 that which must be added to the connotation of the genus, to complete the 

 connotation of the species. 



The word man, for instance, exclusively of what it connotes in common 

 with animal, also connotes rationality, and at least some aj^proximation to 

 that external form which we all know, but which as we have no name for 

 it considered in itself, we are content to call the human. The Differentia, 

 or specific difference, therefore, of man, as referred to the genus animal, is 

 that outward form and the possession of reason. The Aristotelians said, 

 the possession of reason, without the outward form. But if they adhered 

 to this, they would have been obliged to call the Houyhnhnms men. The 

 question never arose, and they were never called upon to decide how such 

 a case would have affected their notion of essentiality. However this may 

 be, they were satisfied with taking such a portion of the diffei'entia as suf- 

 ficed to distinguish the species from all other existing things, though by so 

 doing they might not exhaust the connotation of the name. 



§ 6. And here, to prevent the notion of differentia from being restricted 

 within too narrow limits, it is necessary to remark, that a species, even as 

 referred to the same genus, will not always have tlae same differentia, but 

 a different one, according to the principle and purpose which preside over 

 the particular classification. For example, a naturalist surveys the various 

 kinds of animals, and looks out for the classification of them most in ac- 

 cordance with the order in which, for zoological purposes, he considers it 

 desirable that Ave should think of them. Witli this view he finds it advisa- 

 ble that one of his fundamental divisions should be into warm-blooded and 

 3old-blooded animals ; or into animals which breathe with lungs and those 

 vvhich breathe with gills ; or into carnivorous, and frugivorous or graminiv- 

 orous ; or into those which walk on the flat part and those which walk on 

 ihe extremity of the foot, a distinction on which two of Cuvier's families are 

 "ounded. In doing this, the naturalist creates as many new classes ; which 

 ire by no means those to which the individual animal is familiarly and spon- 

 aneously referred ; nor should we ever think of assigning to them so prom- 

 nent a position in our arrangement of the animal kingdom, unless for a prc- 

 ionccived purpose of scientific convenience. And to the liberty of doing 

 his there is no limit. In the examples we have given, most of the classes 

 .re real Kinds, since each of the peculiarities is an index to a multitude 

 if properties belonging to the class which it characterizes : but even if the 



