i. 2—1. 3. 1 1 



while other natural groups have no popular names ; for instance 

 the groups that we may call Sanguineous and Exsanguineous are 

 not known popularly by any designations. If such natural groups 

 are not to be broken up, the method of Dichotomy cannot be 

 employed, for it necessarily involves such breaking up and disloca- 

 tion. The group of the Many-footed, for instance, would, under 

 this method, have to be dismembered, and some of its kinds 

 distributed among land animals, others among water animals.^ 



(Ch. 3.J Again privative terms inevitably form one branch of 

 dichotomous division, as we see in the proposed dichotomies. But 

 privative terms in their character of privatives admit of no 

 subdivision. For there can be no specific forms of what is non- 

 existent, of Featherless for instance or of Footless, as there are 

 of Feathered and of Footed. Yet a generic differentia must be 

 subdivisible ; for otherwise what is there that makes it generic 

 rather than specific ? There are to be found generic, that 

 is specifically subdivisible, differentiae ; Feathered for instance 

 and Footed. For feathers are divisible into Barbed and Un- 

 barbed, and feet into Many cleft, like those of a bird, or Two- 

 cleft, like those of an ox, or Uncloven and Undivided, like those 

 of a horse. Now even with differentiae capable of this specific 

 subdivision it is difficult enough so to make the classification, as 

 that each animal shall be comprehended in some one subdivision 

 and in not more than one ; but far more difficult, nay impos- 

 sible, is it to do this, if we start with a dichotomy into two 

 contradictories. (Suppose for instance we start with the two 

 contradictories. Feathered and Unfeathered ;^ we shall find that 

 the ant, the glow-worm and some other animals fall under both 

 divisions.) For each differentia must be presented by some 

 species. There must be some species, therefore, under the privative 

 heading. Now specifically distinct animals cannot present in their 

 essence a common undifferentiated element, but any apparently 

 common element must really be differentiated. (Bird and Man 

 for instance are both Two-footed, but their two-footedness is 

 diverse and differentiated. So any two sanguineous groups must 

 have some difference in their blood, if their blood is part of 

 their essence.) From this it follows that a privative term, being 

 insusceptible of differentiation, cannot be a generic differentia ; 

 for, if it were, there would be a common undifferentiated element 



in two different groups.^ 

 643 a. 



