By "nature", Aristotle means the natures of particular things and would perhaps be better translated "a nature." In Book II, however, his appeal to "nature" as a source of activities is more typically to the genera of natural kinds (the secondary substance). But, contra Plato, Aristotle attempts to resolve a philosophical quandary that was well understood in the fourth century. The Eudoxian planetary model sufficed for the wandering stars, but no deduction of terrestrial substance would be forthcoming based solely on the mechanical principles of necessity, (ascribed by Aristotle to material causation in chapter 9). In the Enlightenment, centuries before modern science made good on atomist intuitions, a nominal allegiance to mechanistic materialism gained popularity despite harboring Newton's action at distance, and comprising the native habitat of teleological arguments: Machines or artifacts composed of parts lacking any intrinsic relationship to each other with their order imposed from without. Thus, the source of an apparent thing's activities is not the whole itself, but its parts. While Aristotle asserts that the matter (and parts) are a necessary cause of thingsthe material causehe says that nature is primarily the essence or formal cause (1.193b6), that is, the information, the whole species itself.