Objection 5: Further, if the active intellect is something in the soul, it must be a power. For it is neither a passion nor a habit; since habits and passions are not in the nature of agents in regard to the passivity of the soul; but rather passion is the very action of the passive power; while habit is something which results from acts. But every power flows from the essence of the soul. It would therefore follow that the active intellect flows from the essence of the soul. And thus it would not be in the soul by way of participation from some higher intellect: which is unfitting. Therefore the active intellect is not something in our soul.
On the contrary, The Philosopher says (De Anima iii, 5), that "it is necessary for these differences," namely, the passive and active intellect, "to be in the soul."
I answer that, The active intellect, of which the Philosopher speaks, is something in the soul. In order to make this evident, we must observe that above the intellectual soul of man we must needs suppose a superior intellect, from which the soul acquires the power of understanding. For what is such by participation, and what is mobile, and what is imperfect always requires the pre-existence of something essentially such, immovable and perfect. Now the human soul is called intellectual by reason of a participation in intellectual power; a sign of which is that it is not wholly intellectual but only in part. Moreover it reaches to the understanding of truth by arguing, with a certain amount of reasoning and movement. Again it has an imperfect understanding; both because it does not understand everything, and because, in those things which it does understand, it passes from potentiality to act. Therefore there must needs be some higher intellect, by which the soul is helped to understand.
Wherefore some held that this intellect, substantially separate, is the active intellect, which by lighting up the phantasms as it were, makes them to be actually intelligible. But, even supposing the existence of such a separate active intellect, it would still be necessary to assign to the human soul some power participating in that superior intellect, by which power the human soul makes things actually intelligible. Just as in other perfect natural things, besides the universal active causes, each one is endowed with its proper powers derived from those universal causes: for the sun alone does not generate man; but in man is the power of begetting man: and in like manner with other perfect animals. Now among these lower things nothing is more perfect than the human soul. Wherefore we must say that in the soul is some power derived from a higher intellect, whereby it is able to light up the phantasms. And we know this by experience, since we perceive that we abstract universal forms from their particular conditions, which is to make them actually intelligible. Now no action belongs to anything except through some principle formally inherent therein; as we have said above of the passive intellect (Q[76], A[1]). Therefore the power which is the principle of this action must be something in the soul. For this reason Aristotle (De Anima iii, 5) compared the active intellect to light, which is something received into the air: while Plato compared the separate intellect impressing the soul to the sun, as Themistius says in his commentary on De Anima iii. But the separate intellect, according to the teaching of our faith, is God Himself, Who is the soul's Creator, and only beatitude; as will be shown later on (Q[90], A[3]; FS, Q[3], A[7]). Wherefore the human soul derives its intellectual light from Him, according to Ps. 4:7, "The light of Thy countenance, O Lord, is signed upon us."
Reply to Objection 1: That true light enlightens as a universal cause, from which the human soul derives a particular power, as we have explained.
Reply to Objection 2: The Philosopher says those words not of the active intellect, but of the intellect in act: of which he had already said: "Knowledge in act is the same as the thing." Or, if we refer those words to the active intellect, then they are said because it is not owing to the active intellect that sometimes we do, and sometimes we do not understand, but to the intellect which is in potentiality.
Reply to Objection 3: If the relation of the active intellect to the passive were that of the active object to a power, as, for instance, of the visible in act to the sight; it would follow that we could understand all things instantly, since the active intellect is that which makes all things (in act). But now the active intellect is not an object, rather is it that whereby the objects are made to be in act: for which, besides the presence of the active intellect, we require the presence of phantasms, the good disposition of the sensitive powers, and practice in this sort of operation; since through one thing understood, other things come to be understood, as from terms are made propositions, and from first principles, conclusions. From this point of view it matters not whether the active intellect is something belonging to the soul, or something separate from the soul.
Reply to Objection 4: The intellectual soul is indeed actually immaterial, but it is in potentiality to determinate species. On the contrary, phantasms are actual images of certain species, but are immaterial in potentiality. Wherefore nothing prevents one and the same soul, inasmuch as it is actually immaterial, having one power by which it makes things actually immaterial, by abstraction from the conditions of individual matter: which power is called the "active intellect"; and another power, receptive of such species, which is called the "passive intellect" by reason of its being in potentiality to such species.
Reply to Objection 5: Since the essence of the soul is immaterial, created by the supreme intellect, nothing prevents that power which it derives from the supreme intellect, and whereby it abstracts from matter, flowing from the essence of the soul, in the same way as its other powers.
Whether the active intellect is one in all?
Objection 1: It would seem that there is one active intellect in all. For what is separate from the body is not multiplied according to the number of bodies. But the active intellect is "separate," as the Philosopher says (De Anima iii, 5). Therefore it is not multiplied in the many human bodies, but is one for all men.
Objection 2: Further, the active intellect is the cause of the universal, which is one in many. But that which is the cause of unity is still more itself one. Therefore the active intellect is the same in all.
Objection 3: Further, all men agree in the first intellectual concepts. But to these they assent by the active intellect. Therefore all agree in one active intellect.
On the contrary, The Philosopher says (De Anima iii, 5) that the active intellect is as a light. But light is not the same in the various things enlightened. Therefore the same active intellect is not in various men.
I answer that, The truth about this question depends on what we have already said (A[4]). For if the active intellect were not something belonging to the soul, but were some separate substance, there would be one active intellect for all men. And this is what they mean who hold that there is one active intellect for all. But if the active intellect is something belonging to the soul, as one of its powers, we are bound to say that there are as many active intellects as there are souls, which are multiplied according to the number of men, as we have said above (Q[76], A[2]). For it is impossible that one same power belong to various substances.
Reply to Objection 1: The Philosopher proves that the active intellect is separate, by the fact that the passive intellect is separate: because, as he says (De Anima iii, 5), "the agent is more noble than the patient." Now the passive intellect is said to be separate, because it is not the act of any corporeal organ. And in the same sense the active intellect is also called "separate"; but not as a separate substance.
Reply to Objection 2: The active intellect is the cause of the universal, by abstracting it from matter. But for this purpose it need not be the same intellect in all intelligent beings; but it must be one in its relationship to all those things from which it abstracts the universal, with respect to which things the universal is one. And this befits the active intellect inasmuch as it is immaterial.
Reply to Objection 3: All things which are of one species enjoy in common the action which accompanies the nature of the species, and consequently the power which is the principle of such action; but not so as that power be identical in all. Now to know the first intelligible principles is the action belonging to the human species. Wherefore all men enjoy in common the power which is the principle of this action: and this power is the active intellect. But there is no need for it to be identical in all. Yet it must be derived by all from one principle. And thus the possession by all men in common of the first principles proves the unity of the separate intellect, which Plato compares to the sun; but not the unity of the active intellect, which Aristotle compares to light.
Whether memory is in the intellectual part of the soul?
Objection 1: It would seem that memory is not in the intellectual part of the soul. For Augustine says (De Trin. xii, 2,3,8) that to the higher part of the soul belongs those things which are not "common to man and beast." But memory is common to man and beast, for he says (De Trin. xii, 2,3,8) that "beasts can sense corporeal things through the senses of the body, and commit them to memory." Therefore memory does not belong to the intellectual part of the soul.
Objection 2: Further, memory is of the past. But the past is said of something with regard to a fixed time. Memory, therefore, knows a thing under a condition of a fixed time; which involves knowledge under the conditions of "here" and "now." But this is not the province of the intellect, but of the sense. Therefore memory is not in the intellectual part, but only in the sensitive.
Objection 3: Further, in the memory are preserved the species of those things of which we are not actually thinking. But this cannot happen in the intellect, because the intellect is reduced to act by the fact that the intelligible species are received into it. Now the intellect in act implies understanding in act; and therefore the intellect actually understands all things of which it has the species. Therefore the memory is not in the intellectual part.
On the contrary, Augustine says (De Trin. x, 11) that "memory, understanding, and will are one mind."
I answer that, Since it is of the nature of the memory to preserve the species of those things which are not actually apprehended, we must first of all consider whether the intelligible species can thus be preserved in the intellect: because Avicenna held that this was impossible. For he admitted that this could happen in the sensitive part, as to some powers, inasmuch as they are acts of corporeal organs, in which certain species may be preserved apart from actual apprehension. But in the intellect, which has no corporeal organ, nothing but what is intelligible exists. Wherefore every thing of which the likeness exists in the intellect must be actually understood. Thus, therefore, according to him, as soon as we cease to understand something actually, the species of that thing ceases to be in our intellect, and if we wish to understand that thing anew, we must turn to the active intellect, which he held to be a separate substance, in order that the intelligible species may thence flow again into our passive intellect. And from the practice and habit of turning to the active intellect there is formed, according to him, a certain aptitude in the passive intellect for turning to the active intellect; which aptitude he calls the habit of knowledge. According, therefore, to this supposition, nothing is preserved in the intellectual part that is not actually understood: wherefore it would not be possible to admit memory in the intellectual part.
But this opinion is clearly opposed to the teaching of Aristotle. For he says (De Anima iii, 4) that, when the passive intellect "is identified with each thing as knowing it, it is said to be in act," and that "this happens when it can operate of itself. And, even then, it is in potentiality, but not in the same way as before learning and discovering." Now, the passive intellect is said to be each thing, inasmuch as it receives the intelligible species of each thing. To the fact, therefore, that it receives the species of intelligible things it owes its being able to operate when it wills, but not so that it be always operating: for even then is it in potentiality in a certain sense, though otherwise than before the act of understanding---namely, in the sense that whoever has habitual knowledge is in potentiality to actual consideration.