Article 4 — Whether the agent intellect is something in the soul?

Objection 1: It would seem that the agent intellect is not something in the soul. For the effect of the agent intellect is to give light for the purpose of understanding. But this is done by something higher than the soul: according to John 1:9, He was the true light that enlighteneth every man coming into this world. Therefore the agent intellect is not something in the soul.

Obj. 2: Further, the Philosopher (De Anima iii, 5) says of the agent intellect, that it does not sometimes understand and sometimes not understand. But our soul does not always understand: sometimes it understands, sometimes it does not understand. Therefore the agent intellect is not something in our soul.

Obj. 3: Further, agent and patient suffice for action. If, therefore, the potential intellect, which is a passive power, is something belonging to the soul; and also the agent intellect, which is an active power: it follows that a man would always be able to understand when he wished, which is clearly false. Therefore the agent intellect is not something in our soul.

Obj. 4: Further, the Philosopher (De Anima iii, 5) says that the agent intellect is a substance in actual being. But nothing can be in potentiality and in act with regard to the same thing. If, therefore, the potential intellect, which is in potentiality to all things intelligible, is something in the soul, it seems impossible for the agent intellect to be also something in our soul.

Obj. 5: Further, if the agent 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 agent 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 agent 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 potential and agent intellect, to be in the soul.

I answer that, The agent 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 agent 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 agent 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 agent causes, each one is endowed with its proper powers derived from those universal agent 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 potential 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 agent 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; I-II, 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 Obj. 1: That true light enlightens as a universal cause, from which the human soul derives a particular power, as we have explained.

Reply Obj. 2: The Philosopher says those words not of the agent 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 agent intellect, then they are said because it is not owing to the agent intellect that sometimes we do, and sometimes we do not understand, but to the intellect which is in potentiality.

Reply Obj. 3: If the relation of the agent intellect to the potential 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 agent intellect is that which makes all things (in act). But now the agent 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 agent 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 agent intellect is something belonging to the soul, or something separate from the soul.

Reply Obj. 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 agent intellect; and another power, receptive of such species, which is called the potential intellect by reason of its being in potentiality to such species.

Reply Obj. 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.