Need for an agent intellect

Aquinas on the need for agent intellect:

Aristotle chose a middle course. For with Plato he agreed that intellect and sense are different. But he held that the sense has not its proper operation without the cooperation of the body; so that to sense is not an act of the soul alone, but of the composite. ... But Aristotle held that the intellect has an operation in which the body does not share. Now nothing corporeal can make an impression on the incorporeal. And therefore, in order to cause the intellectual operation, according to Aristotle, the impression caused by sensible bodies does not suffice, but something more noble is required, for the agent is more noble than the patient, as he says. Not, be it observed, in the sense that the intellectual operation is effected in us by the mere impression of some superior beings, as Plato held; but that the higher and more noble agent which he calls the agent intellect, of which we have spoken above, causes the phantasms received from the senses to be actually intelligible, by a process of abstraction. (STh I.84.6 c. Pegis.)