De anima, I, v, 29, where Aristotle seems to assume that intellect is a part, morion, of the soul. Averroes however might have replied that is a mere argumentum ad hominem against Plato, who did suppose so. In n. 25 however Aristotle says clearly, to ginôskein tês psuchês esti k.t.l., which see. But Aristotle is so careless a writer, so regardless of his own injunctions and definitions, that the minute analysis of his language, far from settling a point, may be positively misleading. In reading him you have often to think, not so much of what he says, as of what on his own showing he should say.
When St Thomas teaches that the soul is the form of the body by its substance, but not by the faculty of intelligence, he supposes a real distinction between the soul and its faculties, a distinction not admitted by the earlier scholastics, sometimes called 'Augustinians.' In his ruling that the intelligence has no corporeal organ, one naturally thinks of the brain. But the brain, in the Aristotelian system, had quite another function; it acted as a refrigerator to cool down the vital heat of the body. See the curious chapter, De partibus animalium, II, 7. St Thomas however assigned to the brain some share in sensory processes: see De potentiis animae, cap. iv, quoted in Dr Maher's Psychology, pp. 568-9, ed. 4.
Of God and His Creatures: 2.69