 In the Physics, Aristotle builds on his general account of the four causes by developing explanatory principles that are specific to the study of nature. Here Aristotle insists that all four causes are involved in the explanation of natural phenomena, and that the job of “the student of nature is to bring the why-question back to them all in the way appropriate to the science of nature” (Phys. 198 a 21–23). The best way to understand this methodological recommendation is the following: the science of nature is concerned with natural bodies insofar as they are subject to change, and the job of the student of nature is to provide the explanation of their natural change. The factors that are involved in the explanation of natural change turn out to be matter, form, that which produces the change, and the end of this change. Note that Aristotle does not say that all four explanatory factors are involved in the explanation of each and every instance of natural change. Rather, he says that an adequate explanation of natural change may involve a reference to all of them.