  Given that the soul is, according to Aristotle's theory, a system of abilities possessed and manifested by animate bodies of suitable structure, it is clear that the soul is, according to Aristotle, not itself a body or a corporeal thing. Thus Aristotle agrees with the Phaedo's claim that souls are very different from bodies. Moreover, Aristotle seems to think that all the abilities that are constitutive of the souls of plants, beasts and humans are such that their exercise involves and requires bodily parts and organs. This is obviously so with, for instance, the abilities for movement in respect of place (e.g., by walking or flying), and for sense-perception, which requires sense-organs. Aristotle does not, however, think that there is an organ of thought, and so he also does not think that the exercise of the ability to think involves the use of a bodily part or organ that exists specifically for this use. Nevertheless, he does seem to take the view that the activity of the human intellect always involves some activity of the perceptual apparatus, and hence requires the presence, and proper arrangement, of suitable bodily parts and organs; for he seems to think that sensory impressions [phantasmata] are somehow involved in every occurrent act of thought, at least as far as human beings are concerned (De Anima 3.7, 431a14-7; 3.8, 432a7-10; cf. De Memoria 1, 449b31ff.). If so, Aristotle in fact seems to be committed to the view that, contrary to the Platonic position, even human souls are not capable of existence and (perhaps as importantly) activity apart from the body (cf. De Anima 1.1, 403a3-25, esp. 5-16).