De Anima II,4 opens Aristotle’s investigation of the various psychic faculties with the basic capacity shared by plants and animals alike: nutritive soul. He announces a three-step approach to be extended from nutritive soul to perceptive soul and intellect: to define a psychic faculty, first examine the functions it enables, and to understand the functions, examine the correlative objects − in the case of nutrition, food. This paper examines how the methodological prescriptions apply to nutritive soul and, focusing on the function of organic selfmaintenance, argues that although the investigation of nutritive soul fits the stated program − food, self-maintenance, nutritive capacity − the order of investigation is the reverse of the order of explanation: the faculty is causally prior to the activity it enables, and the activity is prior to the correlative object, which is merely instrumental to that activity and to the psychic capacity. Moreover, the faculty is causally prior to its functions in three ways, as formal, final, and efficient cause. The paper does not speculate as to how the method extends to other psychic functions, but its analysis raises a question: Will Aristotle’s treatment of the higher faculties fit the prescribed method, and if so how?