  For the purposes of understanding Aristotle’s psychology, the origin of Aristotle’s hylomorphism is significant for two reasons. First, from its inception, Aristotle’s hylomorphism exploits two distinct but related notions of form, one of which is essential to the compound whose form it is, and the other of which is accidental to its subject.  In advancing his view of the soul and its capacities, Aristotle employs both of these notions: the soul is an essential form, whereas perception involves the acquisition of accidental forms. Second, because Aristotle’s hylomorphism was initially developed to handle puzzles of change and generation, its deployment in philosophical psychology is sometimes strained, insofar as Aristotle is not immediately willing to treat every instance of perception and thought as a straightforward instance of change in some continuing subject.  Moreover, as we shall see, it is sometimes difficult to appreciate how Aristotle can justifiably regard the body as the matter of a human being in the way that the bronze is held to be the matter of a statue.  Bronze can exist as an indeterminate lump, being potentially but not actually the statue of a great hero. There is no ready analogue in the case of the body: the body is not so much stuff lying about waiting to be enformed by a soul. Rather, in one important sense, human bodies become human bodies by being ensouled. If so, then they seem ill-suited to play the role of matter in precisely those terms given by Aristotle’s hylomorphic theory of generation.