Abstract: Aristotle, in the Historia Animalium, follows (and modifies) the explanation-involving approach to classification that he developed in the pattern of the Posterior Analytics. Thus, he draws in his theory of animal classification on his explanatory account of soul functions developed in De Anima. However, his project encounters a severe problem: he failed to uncover in his study of biological phenomena the unified, causally basic essences that his theory of definition required. I consider whether Aristotle can resolve this crisis while remaining true to the basic features of his Analytics paradigm.

Keywords: Aristotle, biological classification, classification, common nature, De Partibus Animalium, definition, division, explanation, Historia Animalium, species,