 The logical doctrine of classification, as it stands in the ordinary text-books, implies a certain definite connexion between these two characteristics of the concept: namely that if a genus is distinguished into a certain number of species, the class of its instances can be correspondingly divided into an equal number of sub-classes. Each sub-class will comprise the instances of one specific concept; the totality of the sub-classes will comprise that of the generic concept… (EPM 2005: 29)