 A second limitation of division is its indifference to the distinction between causally fundamental characteristics and proper attributes, to use the language of the Analytics. Yet, being able to distinguish these is absolutely fundamental to Aristotelian science. A careful comparative study of the History of Animals, on the one hand, and works such as On the Parts or On the Generation of Animals, on the other, provides insight into how Aristotle understands and deploys this distinction in his actual scientific practice. And as we have seen above, Aristotle draws explicit attention to its importance for his biological investigations in a number of key texts within those investigations themselves. To study in detail the interplay between definition, causal demonstration and division in the biology is to see Aristotle working through just those problems which form the central question of Posterior Analytics II—how precisely are definition, causal demonstration and division related to one another in the quest for, and achievement of, scientific understanding?