3. If the intellect were a corporeal power, it would be affected by its object and injured by a powerful stimulus, as is the case in the senses of sight and hearing. A dazzling light injures the eye, a deafening noise injures the ear, so that thereafter neither sense can perform its normal function properly. This is not true with the intellect. An unusually difficult subject of thought does not injure the intellect.
4. If the intellect were similar in its activity to sense perception, it would not be self-conscious, as the sense faculties cannot perceive themselves.
5. The intellect, if it were like sense, would not be able to comprehend a thing and its opposite at the same time, or it would do so in a confused manner, as is the case in the powers of sense.
6. The intellect perceives universals; the sense, particulars.
This being the case, there is a difference of opinion as to the nature of the material intellect. Some say that it has no definite nature in itself except that of possibility and capacity, though it is different from other possibilities in this respect that it is not resident in, and dependent upon a material subject like the others. That is why Aristotle says that the material intellect is not anything before it intellects; that it is in its essence potential with reference to the intelligibilia, and becomes actual when it understands them actually.
Themistius says it is not any of the existents actually, but a potential essence receiving material forms. Its nature is analogous to that of prime matter; hence it is called material intellect. It is best to call it possible intellect. Being a potential existent it is not subject to generation and dissolution any more than prime matter.
Alexander of Aphrodisias thinks the material intellect is only a capacity, i. e., a power in the soul, and appears when the soul enters the body, hence is not eternal a parte ante.
Averroes holds that the possible intellect is a separate substance, and that the capacity is something it has by virtue of its being connected with the body as its subject. Hence this capacity is neither entirely distinct from it nor is it identical with it. According to him the possible intellect is not a part of the soul.
Which of these views is correct, says Hillel, requires discussion, but it is clear that whichever of these we adopt there is no reason opposing the conjunction of the possible intellect with the Active. For if it is an eternal substance, potential in its nature, like primary matter, then it becomes actual when it understands the intelligible objects. The same is true if it is a capacity residing in the soul.
Hillel is thus of the opinion in this other question debated in those days, whether the intellect of man is capable of conjunction during life with the angelic Active Intellect, that it is. The Active Intellect, he says, in actualizing the material intellect influences it not in the manner of one body acting upon another, i. e., in the manner of an efficient or material cause, but rather as its formal or final cause, leading it to perfection. It is like the influence which the separate Intelligences receive from one another, the influence of emanation, and not a material influence comparable to generation. This reception of influence from the Active Intellect on the part of the potential is itself conjunction. It means that the agent and the thing acted upon become one, and the same substance and species. The material intellect becomes a separate substance when it can understand itself.[326]