Until now we have spoken of the passive understanding, which is the nature of the soul, but also in equal degree its faculty of sense-perception and imagination. Aristotle now proceeds to distinguish active understanding from this, as follows (De Anima, III. 5): “In nature as a whole there is present in every species of things, on the one hand, matter, which in potentiality is the whole of this species, and, on the other hand, cause and energy, operative in all things, in the same way that art is related to matter. It therefore necessarily follows that in the soul also these different elements should be present. The faculty of understanding is thus, in one view of it, the capacity of becoming all things; but in another view it is the capacity of creating all things, as is done by an efficient power (ἕξις), light, for instance, which first causes the colours which exist in potentiality to exist in reality. This understanding is absolute (χωριστός), uncompounded, and not influenced from without, as it is essentially activity. For the active is always more in honour than the passive, and the principle more in honour than the matter that it forms. Knowledge, when in active exercise, is identical with the thing (πρᾶγμα) known; but what is in potentiality” (that is, external reason, imagination, sense-perception) “is certainly prior in respect of time in one and the same individual, but in the universal (ὅλως) it is not even so in respect of time. Active understanding is not such that it sometimes thinks and sometimes does not. When it is absolute, it is the one and only existence; and this alone is eternal and immortal. We, however, do not remember this process, because this understanding is unaffected from without; but the passive understanding is transitory, and without the former it is incapable of thought.”
The seventh and eighth chapters are expositions of the maxims contained in the fourth and fifth; they begin with these maxims, and have the appearance of being from the hand of a commentator. “The soul,” says Aristotle (De Anima, III. 8), “is in a certain sense the whole of existence. For existent objects are either perceived by the senses or thought; but knowledge itself is in a manner the object of knowledge, and perception the object of perception. What are known and perceived are either the things themselves or their forms. Knowledge and sense-perception are not the things themselves (the stone is not in the soul), but their form; so that the soul is like the hand. As this is the instrument by which we grasp instruments, so the understanding is the form by which we apprehend forms, and sense-perception the form of the objects cf sense.” Before this Aristotle had remarked (De Anima, III. 4): “It has been truly said that the soul is the _place of ideas_ (τόπος εἰδῶν): not the whole soul, but only the thinking soul, and these ideas do not exist in the soul actually, but only potentially.” That is to say, the ideas are at first only quiescent forms, not activities, and so Aristotle is not a realist. But the understanding makes these forms, like those of external nature, its objects, its thoughts, its potentiality, Aristotle therefore says in the seventh chapter: “The understanding thinks the abstract (τὰ ἐν ἀφαιρέσει λεγόμενα), just as it conceives snubnosedness not as snubnosedness that cannot be separated from the flesh, but as hollowness.” Then in the eighth chapter Aristotle goes on to say: “But as no object is separated from its perceived dimensions, so in the forms perceived by sense there are also objects of thought, both abstract conceptions and the qualities (ἕξεις) and determinations of the objects of sense. In this way he who perceives nothing by his senses learns nothing and understands nothing; when he discerns anything (θεωρῇ), he must necessarily discern it as a pictorial conception, for such conceptions are like sense-perceptions, only without matter. In what way then are our primary ideas distinguished, so as not to be mistaken for conceptions? Or is it not the case also that other thoughts even are not pictorial conceptions, but only that they are never found unassociated with such conceptions?” Since what follows contains no answer to the questions raised here at the very end, this would seem an additional indication that these portions follow later.[100] Aristotle concludes the seventh chapter with the words: “Speaking generally, the understanding is the faculty which thinks things in their real activity. Whether, however, it can think the absolute or not, unless it be itself separated from the sensuous, we shall inquire later (ὕστερον).” This “later” Buhle considers to have reference to the “highest philosophy.”[101]