178 NAMES AND PROPOSITIONS. 



particular essay or treatise, and becomes the differentia 

 of the species*. 



The differentia, therefore, of a species, may be 

 defined to be, that part of the connotation of the 

 specific name, whether ordinary, or special and tech- 

 nical, which distinguishes the species in question from 

 all other species of the genus to which on the par- 

 ticular occasion we are referring it. 



7. Having disposed of Genus, Species, and 

 Differentia, we shall not find much difficulty in attain- 

 ing a clear conception of the distinction between the 

 other two predicables. 



In the Aristotelian phraseology, Genus and Dif- 

 ferentia are of the essence of the subject ; by which, as 

 we have seen, is really meant that the properties 

 signified by the genus and those signified by the 

 differentia, form part of the connotation of the name 

 denoting the species. Proprium and Accidens, on the 

 other hand, form no part of the essence, but are 

 predicated of the species only accidentally. Both are 

 Accidents in the wider sense, in which the accidents of 

 a thing are opposed to its essence ; although, in the 

 doctrine of the Predicables, Accident is used for one 

 sort of accident only, Proprium being another sort. 

 Proprium, continue the schoolmen, is predicated 

 accidentally, indeed, but necessarily; or, as they fur- 

 ther explain it, signifies an attribute which is not 



* If we allow a differentia to what is not really a species. For 

 the distinction of Kinds, in the sense explained by us, not being in 

 any way applicable to attributes, it of course follows that although 

 attributes may be put into classes, those classes can be admitted to 

 be genera or species only by courtesy. 



