That it is not impossible for the Potential and the Active Intellect to be united in the one Substance of the Soul

SOME one perhaps may think it impossible for one and the same substance, that of our soul, to be in potentiality to receive all intellectual impressions (which is the function of the potential intellect), and to actualise those impressions (which is the function of the active intellect); since nothing acts as it is in potentiality to receive, but only as it is in actual readiness to act. But, looking at the matter rightly, no inconvenience or difficulty will be found in this view of the union of the active and potential intellect in the one substance of the soul. For a thing may well be in potentiality in one respect and in actuality in another; and this we find to be the condition of the intellectual soul in its relation to phantasms, or impressions in phantasy. For the intellectual soul has something in actuality, to which the phantasm is in potentiality;* and on the other hand the intellectual soul is in potentiality to that which is actually found in the phantasms.* For the substance of the human soul has the attribute of immateriality: but it is not thereby assimilated to this or that definite thing; and yet such assimilation is requisite for our soul to know this or that thing definitely, since all cognition takes place by some likeness of the object known being stamped on the knowing mind.* Thus then the intellectual soul remains in potentiality, open to the reception of definite impressions in the likeness of things that come within our observation and knowledge, which are the natures of sensible things. These definite natures of sensible things are represented to us by phantasms, which however have not yet reached the stage of being objects of intellect, seeing that they are likenesses of sensible things under material conditions, which are individualising properties, -- and besides they are in bodily organs. They are therefore not actual objects of understanding; and yet since in the case of this man [or other sensible object], whose likeness is represented by phantasms, it is possible to fix upon a universal nature stripped of all individualising conditions, these phantasms are potentially intelligible. Thus then they have a potentially intelligible being, but an actually definite likeness to things, whereas in the intellectual soul, as we saw, the situation was the other way about. There is then in the intellectual soul a power exercising its activity upon phantasms, making them actual objects of understanding; and this power of the soul is called the active intellect. There is also in the soul a power that is potentially open to definite impressions of sensible things; and this power is the potential intellect.

But the intellectual soul does not lie open to receive impressions of the likenesses of things that are in phantasms in the way that the likeness exists in the phantasm, but according as those likenesses are raised to a higher stage, by being abstracted from individualising material conditions and rendered actual objects, or terms, of understanding. And therefore the action of the active intellect upon the phantasms precedes their being received into the potential intellect; and thus the prime agency is not attributable to the phantasms, but to the active intellect.

There are some animals that see better by night than by day, because they have weak eyes, which are stimulated by a little light, but dazzled by much. And the case is similar with our understanding, which is "to the clearest truths as the bat's eye to the sun" (Aristotle, Metaph. I, Appendix): hence the little intellectual light that is connatural to us is sufficient for us to understand with. But that the intellectual light connatural to our soul is sufficient to produce the action of the active intellect, will be clear to any one who considers the necessity for positing such an intellect. Our soul is found to be in potentiality to intelligible objects as sense to sensible objects: for as we are not always having sensations, so we are not always understanding.* These intelligible objects Plato assumed to exist by themselves, calling them 'Ideas': hence it was not necessary for him to posit any 'active intellect' rendering objects intelligible.* But if this Platonic position were true, the absolutely better objects of intelligence should be better also relatively to us, and be better understood by us, which is manifestly not the case: for things are more intelligible to us which are nigher to sense, though in themselves they are less excellent objects of understanding. Hence Aristotle was moved to lay down the doctrine, that the things which are intelligible to us are not any self-existent objects of understanding, but are gathered from objects of sense. Hence he had to posit some faculty to do this work of making terms of understanding: that faculty is the active intellect. The active intellect therefore is posited to make terms of understanding proportionate to our capacity. Such work does not transcend the measure of intellectual light connatural to us. Hence there is no difficulty in attributing the action of the active intellect to the native light of our soul, especially as Aristotle compares the active intellect to light (De anima, III, v, 2).

2.76 : That the Active Intellect is not a separately Subsisting Intelligence, but a Faculty of the Soul
2.78 : That it was not the Opinion of Aristotle that the Active Intellect is a separately Subsistent Intelligence, but rather that it is a Part of the Soul