CLASSIFICATION AND THE PREDICABLES. 103 



is part of its meaning in the 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 sjDecies of 

 the genus to which on the particular occasion we are referring it. 



§ 7. Having disposed of Genus, Species, and Differentia, we shall not find 

 much difficulty in attaining a clear conception of the distinction between 

 the other two predicables, as well as between them and the first three. 



In the Aristotelian phraseology, Genus and Differentia are of the essence 

 of the subject; by which, as we have seen, is really meant that the proper- 

 ties signified by the genus and those signified by the differentia, form part 

 of the connotation of the name denoting the species. Proprium and Ac- 

 cidens, 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 ; though, in the 

 doctrine of the Predicables, Accidens is used for one sort of accident only, 

 Proprium being another sort. Proprium, continue the schoolmen, is pred- 

 icated accidentally, indeed, but necessarily; or, as they further explain it, 

 signifies an attribute which is not indeed part of the essence, but which 

 flows from, or is a consequence of, the essence, and is, therefore, inseparably 

 attached to the species ; e. g., the various properties of a triangle, which, 

 though no part of its definition, must necessarily be possessed by whatever 

 comes under that definition. Accidens, on the contrary, has no connection 

 whatever with the essence, but may come and go, and the species still re- 

 main what it was before. If a species could exist without its Propria, it 

 must be capable of existing without that on which its Propria are neces- 

 sarily consequent, and therefore without its essence, without that which con- 

 stitutes it a species. But an Accidens, whether separable or inseparable 

 from the species in actual exj^erience, may be supposed separated, without 

 the necessity of supposing any other alteration ; or at least, without sup- 

 posing any of the essential properties of the species to be altered, since 

 with them an Accidens has no connection. 



A Proprium, therefore, of the species, may be defined, any attribute which 

 belongs to all the individuals included in the species, and which, though 

 not connoted by the specific name (either ordinarily if the classification we 

 are considering be for ordinary purposes, or specially if it be for a special 

 purpose), yet follows from some attribute which the name either ordinarily 

 or specially connotes. 



One attribute may follow from another in two ways ; and there are con- 

 sequently two kinds of Proprium. It may follow as a conclusion follows 

 premises, or it may follow as an effect follows a cause. Thus, the attribute 

 of having the opposite sides equal, which is not one of those connoted by 

 the word Parallelogram, nevertheless follows from those connoted by it, 

 namely, from having the opposite sides straight lines and parallel, and the 

 number of sides four. The attribute, therefore, of having the opposite 

 sides equal, is a Proprium of the class parallelogram ; and a Proprium of 

 the first kind, which follows from the connoted attributes by way of dem- 



* If we allow a differentia to what is not really a species. For the distinction of Kinds, 

 n the sense explained by us, not being in any way applicable to attributes, it of course follows 

 hat although attributes may be put into classes, those classes can be admitted to be genera 

 )r species only by courtesy. 



