 In the Aristotelian tradition, Ibn Rushd postulates a special sort of substantial form—a soul—to account for living substances. Even in the mundane case of plants, the complexities of their operations require a special principle beyond what would be adequate for nonliving things: nutrition, for instance, “is ascribed to the soul because it is impossible for it to be ascribed to the powers of the elements” (LongAnima II.14). His theory of the soul’s operations distinguishes, most basically, between the nutritive, sensory, and rational levels. Judging from his casually flexible terminology, he sees no real difference between treating these as different souls within a single living thing or as parts of a single soul—parts characterized as a power (quwwa) or principle (mabdaʾ). Judging again from his varying formulations, he thinks there can be no definitive list of how many such powers of the soul there are. The question he does regard as meaningful is whether a power is distinguished solely in terms of its function, or also in terms of its substrate—as he puts it, whether it “differs from the other powers in subject as well as in intention (maʿnā), or only in intention” (LongAnima III.1; ParaAnima ¶276). Each of the five external senses, for instance, has its own subject, a sensory organ, whereas some of the higher sensory operations have dedicated organs, in the brain, whereas other operations, such as recollection (Black 1996) and choice (Phillipson 2013), are mere functions produced by multiple powers working in conjunction. This question of “subject” is particularly vexed, as we will see, for the powers of intellect.