... Augustine deliberately removes from divine illumination any knowledge which our intellect might abstract from the sensible and even denies that our intellect can have the sensible as its object. Only reason has dealings with the sensible; as for the intellect, it busies itself only with the intelligible order and has nothing to abstract from material things. The divine light it receives is not given it for that purpose. But, if illumination does not abstract, what does it do? [84. Clear distinction between reason and intellect. So, at least as far as Augustine is concerned, keep this very Platonic distinction in mind: reason deals with the sensible, intellect with the intelligible.]
Of this question we can say without exaggeration that it has tested the acumen of many generations of historians. The most obvious postulate for the problem is that there are no postulates. Augustine tells us neither how the intellect operates nor what it does. Some historians say simply that this is a serious lacuna; others, while admitting that Augustine said nothing of the sort, do their utmost to fill the lacuna by attributing to Augustine's thought an abstractive activity such as we have mentioned.... However, it seems to me that there is a simpler hypothesis to consider, namely that there is no lacuna here provided we look at things from Augustine's point of view and refuse to base our arguments on principles he did not accept. Actually, in Augustine there is no problem involving an Umsetzung (transformation) of the sensible into the intelligible. If he did not solve this problem, the reason was that he had no such problem to solve. If we insist that he solve it, then we do not fill a lacuna in his doctrine but change it into something else and in doing so take on ourselves the responsibility of foisting it on him. [84.]
Let us remember first of all that Augustine's interest lies not so much in the formation of a concept as in the formation of a knowledge of truth. In his teaching, everything happens as if there were no need to account for the general character of general ideas. Instead of finding fault with him for this or remedying this situation more or less arbitrarily, we might do well to see why he was not struck by the importance of the problem.
Augustine thinks of the universe as matter in which the divine ideas / have implanted the intelligible.... Strictly speaking, the universe is intelligible to a mind that is capable of knowing it as such. Now it is very true that the world of things, by reason of its corporeity, cannot enter the mind, which is hierarchically superior to it, and for this reason abstraction properly so called is impossible in such a doctrine.There is no communication between substances in the direction of body to soul, but owing to the superiority of the soul over the body, there can be communication between substances in the direction of soul to body.... Because of this, the Augustinian soul can decipher directly, in the numbers of the changes undergone by its body, the numbers of the exterior bodies which produce these changes.... In order to have Aristotelian abstraction in Augustinism, we should have to find a place for the action of body on soul, and there is no place for it. In order to have in Augustinism a vision in God such as Malebranche proposed, we should have to do away with its direct communication of soul with body, and this is a power which Augustine always accorded the soul by reason of its transcendence alone. Between these two opposing conceptions, Augustinism remains what it was: a doctrine in which mind can read the intelligible directly in the image and consequently need do nothing more than discover where the source of truth is to be found. [84-5.]
As an historian, and he could be a good one, Saint Thomas saw clearly that, if we introduce an agent intellect into Plato's universe, it cannot have the same functions there as it had in Aristotle's universe. in an Aristotelian world, an agent intellect is needed to effect the intelligible, and this is the task of abstraction. In a Platonic world, on the other hand, an agent intellect is not needed to produce intelligibles because the human intellect finds them ready-made in its images; it is needed only to bestow the intelligible light on the understanding subject. Illumination of the mind by God in Augustinism, in Aristotelianism illumination of the object by a mind which God illumines; here is the difference between illumination-truth and illumination-abstraction. [86.]
Thus it seems true to say - salve meliore judicio - that illumination as Augustine saw it has as its exact point of application not so much the power to conceive as the power to judge, because in his view the intelligibility of the concept resides rather in the normative character which its own necessity bestows on the concept than in the general character of its extension. [91.]