To understand the passions, one must know “where” the passions are located in a human being. This requires Aquinas to identify the “seat” or “subject” of the passions. Thomas identifies the subject of the passions as the “sensitive appetite.” When Aquinas speaks of the sensitive appetite, he supposes its place in a more comprehensive teaching about the soul and its powers. Setting the “vegetative” and “locomotive” powers of the soul aside, we may focus on what Aquinas means by the core notion of “appetite” (§1.1). Though “appetite” does have a univocal meaning, it is irreducibly differentiated into three types–natural, rational, and sensitive. Aquinas gives a preliminary explanation of sensitive appetite by situating it “between” natural appetite (§1.2) and rational appetite (§1.3). Why does Thomas hold that the primary object of appetite is good, and that there is no appetite for evil as such? Aquinas's teaching on the priority of good over evil provides the first clue for understanding why he orders the passions in the manner that he does (§1.4).