  It is crucially important not to misunderstand these various faculties as parts or aspects of the mind, items that operate with some degree of autonomy from one another and can therefore conflict. On the Stoic theory, the faculties of the mind are simply things the mind can do.  Moreover, it is a central part of the theory that, in the case of an adult human being, there is no such thing as an impulse without an act of assent of the mind to a corresponding practical impression. In a rational subject, the faculty of impulse depends on the faculty of assent, which, like all faculties of such a subject, is a rational faculty. This theory leaves no room for the Platonic conception that the souls of adult human beings contain non-rational parts which can, and frequently do, generate impulse and behavior independently of, and even contrary to, the designs and purposes of reason. Nor, relatedly, does it leave room for the shared Platonic and Aristotelian view that desire, even in the case of adult humans, comes in three forms, two of which are such that desires of these forms do not arise from, or depend on, activities of reason. The Stoic theory has the attractive consequence that each adult person is, through their own reasoned assent, unambiguously and equally responsible for all their voluntary behavior: there are no Platonic nonrational parts, or Platonic-Aristotelian nonrational desires, that could produce actions against one's own reason's helpless protestations. However, the theory needed to be defended both against rival philosophical theories and against pre-theoretical intuitions that militate in favor of these theories. One such intuition is that passion can, and frequently does, conflict with reason. To judge from a report by Plutarch, it appears that the Stoics were able to explain away this particular intuition, and also to disarm the argument for tripartition of the soul in Republic 4, which depends on the simultaneity of a desire for and an aversion to one and the same thing. According to Plutarch (L&amp;S 65G1),