Yesterday, I brought up some difficulties that occur in the first method of division presented in Aristotle’s Parts of Animals.
“Some construe the individual species by dividing the group into two differentiae. In one way this is not easy, in another impossible. For of some there will be only one differentia, but the other terms will be superfluous, such as in the case of footed, two-footed, footed with parted toes. For this last differentia alone is proper” (Parts of Animals, 642b5-9)?
Before discussing the difficulties again, it must be taken into consideration, of course, that since he is embarking on a criticism of Academic methodology, any philosophical difficulties arising from this process of division might in fact owe to chinks in the armor which Aristotle himself was trying to illuminate. He might very well be bringing some of these difficulties to light without proceeding to explain them.
A couple of the difficulties I brought up yesterday were:
“It is not true that the concept of “footed with parted toes” includes “two footed” and “footed.” viz. lizards
It is also clear from his use of the term elsewhere, that “footed with parted toes (σχιζόπους)” is not meant to designate any particular species alone, such as humans (cf. HA 593a28, concerning birds).”
A mistake one could make, at least in Aristotle’s construal of the division, is failing to recognize that at every point of the division a particular animal is being guided through each step of the division. So, in this example, one has to have in mind a particular animal which one leads through each “gate” of the division. There is no abstracted “two-footed,” in other words; differentiae always belong to real animals. (This is one reason why Aristotle says shortly that there cannot be divisions of non-being, for no animals correspond to such a division.)
In fact, Aristotle will return to this division at 643b29 ff. He says there two interesting things. He affirms that with this method both (a) that only one differentia will be arrived at (b) it is impossible for one differentia to be adequate for a species. In light of this he brings up the same “footed, two-footed, footed with parted toes,” tri-partite division. Only this time he applies it to “man” (ἄνθρωπος). He points out that man is many other things besides possessing parted toes.
Both of these judgments merge into a single criticism: there is a need for there to be multiple differentia, although the Academic method cannot allow for it, it is not so much wrong, as it is inadequate. One reason for a need for more lines of division is that there are many homologous features in animals. Similar body plans, parts, and functions means that there will be many animals with split-toed feet. Because of this diversity there will be a corresponding need for a robust method of division.