 Chapters 2 and 3 have a similar narrative structure. Gradually, a positive theory of biological division emerges from the ashes of a detailed critical analysis of those (Plato and certain of his students) who “attempt to grasp the particular by dividing the kind into two differences” (642b5), a practice he finds in “the written divisions” (642b11), perhaps a reference to divisions we find in some of Plato’s later dialogues, or perhaps to lost works by other members of Plato’s Academy. The method he is criticizing combines two basic techniques that lead to things being grouped together that are fundamentally different and things being grouped separately that are fundamentally similar: dichotomy and division by non-essentials. Dichotomy is the method of dividing the more general differentia into two exhaustive alternatives, which often entails that one of the alternatives is simply the privation of the other (winged, wingless). Division by non-essentials involves dividing a prior differentia-class by means of an unrelated difference. For example, you might first divide animals into winged and wingless, and then winged animals into wild and tame.