Summa Theologica, Part I (Prima Pars) From the Complete...

After considering what belongs to the angel's substance, we now proceed to his knowledge. This investigation will be fourfold. In the first place inquiry must be made into his power of knowledge: secondly, into his medium of knowledge: thirdly, into the objects known: and fourthly, into the manner whereby he knows them.

Objection 1: It would seem that the angel's act of understanding is his substance. For the angel is both higher and simpler than the active intellect of a soul. But the substance of the active intellect is its own action; as is evident from Aristotle (De Anima iii) and from his Commentator [*Averroes, A.D. 1126-1198]. Therefore much more is the angel's substance his action—that is, his act of understanding.

Obj. 2: Further, the Philosopher says (Metaph. xii, text 39) that "the action of the intellect is life." But "since in living things to live is to be," as he says (De Anima ii, text 37), it seems that life is essence. Therefore the action of the intellect is the essence of an angel who understands.

Obj. 3: Further, if the extremes be one, then the middle does not differ from them; because extreme is farther from extreme than the middle is. But in an angel the intellect and the object understood are the same, at least in so far as he understands his own essence. Therefore the act of understanding, which is between the intellect and the thing understood, is one with the substance of the angel who understands.

On the contrary, The action of anything differs more from its substance than does its existence. But no creature's existence is its substance, for this belongs to God only, as is evident from what was said above (Q. 3, A. 4). Therefore neither the action of an angel, nor of any other creature, is its substance.

I answer that, It is impossible for the action of an angel, or of any creature, to be its own substance. For an action is properly the actuality of a power; just as existence is the actuality of a substance or of an essence. Now it is impossible for anything which is not a pure act, but which has some admixture of potentiality, to be its own actuality: because actuality is opposed to potentiality. But God alone is pure act. Hence only in God is His substance the same as His existence and His action.

Besides, if an angel's act of understanding were his substance, it would be necessary for it to be subsisting. Now a subsisting act of intelligence can be but one; just as an abstract thing that subsists. Consequently an angel's substance would neither be distinguished from God's substance, which is His very act of understanding subsisting in itself, nor from the substance of another angel.

Reply Obj. 1: When the active intellect is said to be its own action, such predication is not essential, but concomitant, because, since its very nature consists in act, instantly, so far as lies in itself, action accompanies it: which cannot be said of the passive intellect, for this has no actions until after it has been reduced to act.

Reply Obj. 2: The relation between "life" and "to live" is not the same as that between "essence" and "to be"; but rather as that between "a race" and "to run," one of which signifies the act in the abstract, and the other in the concrete. Hence it does not follow, if "to live" is "to be," that "life" is "essence." Although life is sometimes put for the essence, as Augustine says (De Trin. x), "Memory and understanding and will are one essence, one life": yet it is not taken in this sense by the Philosopher, when he says that "the act of the intellect is life."

Reply Obj. 3: The action which is transient, passing to some extrinsic object, is really a medium between the agent and the subject receiving the action. The action which remains within the agent, is not really a medium between the agent and the object, but only according to the manner of expression; for it really follows the union of the object with the agent. For the act of understanding is brought about by the union of the object understood with the one who understands it, as an effect which differs from both. _______________________

Objection 1: It would seem that in the angel to understand is to exist. For in living things to live is to be, as the Philosopher says (De Anima ii, text. 37). But to "understand is in a sense to live" (De Anima ii, text. 37). Therefore in the angel to understand is to exist.

I answer that, The action of the angel, as also the action of any creature, is not his existence. For as it is said (Metaph. ix, text. 16), there is a twofold class of action; one which passes out to something beyond, and causes passion in it, as burning and cutting; and another which does not pass outwards, but which remains within the agent, as to feel, to understand, to will; by such actions nothing outside is changed, but the whole action takes place within the agent. It is quite clear regarding the first kind of action that it cannot be the agent's very existence: because the agent's existence is signified as within him, while such an action denotes something as issuing from the agent into the thing done. But the second action of its own nature has infinity, either simple or relative. As an example of simple infinity, we have the act "to understand," of which the object is "the true"; and the act "to will," of which the object is "the good"; each of which is convertible with being; and so, to understand and to will, of themselves, bear relation to all things, and each receives its species from its object. But the act of sensation is relatively infinite, for it bears relation to all sensible things; as sight does to all things visible. Now the being of every creature is restricted to one in genus and species; God's being alone is simply infinite, comprehending all things in itself, as Dionysius says (Div. Nom. v). Hence the Divine nature alone is its own act of understanding and its own act of will.

Reply Obj. 1: Life is sometimes taken for the existence of the living subject: sometimes also for a vital operation, that is, for one whereby something is shown to be living. In this way the Philosopher says that to understand is, in a sense, to live: for there he distinguishes the various grades of living things according to the various functions of life.

Reply Obj. 2: The essence of an angel is the reason of his entire existence, but not the reason of his whole act of understanding, since he cannot understand everything by his essence. Consequently in its own specific nature as such an essence, it is compared to the existence of the angel, whereas to his act of understanding it is compared as included in the idea of a more universal object, namely, truth and being. Thus it is evident, that, although the form is the same, yet it is not the principle of existence and of understanding according to the same formality. On this account it does not follow that in the angel "to be" is the same as 'to understand.' _______________________

Objection 1: It would seem that in an angel the power or faculty of understanding is not different from his essence. For, "mind" and "intellect" express the power of understanding. But in many passages of his writings, Dionysius styles angels "intellects" and "minds." Therefore the angel is his own power of intelligence.

Obj. 2: Further, if the angel's power of intelligence be anything besides his essence, then it must needs be an accident; for that which is besides the essence of anything, we call it accident. But "a simple form cannot be a subject," as Boethius states (De Trin. 1). Thus an angel would not be a simple form, which is contrary to what has been previously said (Q. 50, A. 2).

Obj. 3: Further, Augustine (Confess. xii) says, that God made the angelic nature "nigh unto Himself," while He made primary matter "nigh unto nothing"; from this it would seem that the angel is of a simpler nature than primary matter, as being closer to God. But primary matter is its own power. Therefore much more is an angel his own power of intelligence.

I answer that, Neither in an angel nor in any creature, is the power or operative faculty the same as its essence: which is made evident thus. Since every power is ordained to an act, then according to the diversity of acts must be the diversity of powers; and on this account it is said that each proper act responds to its proper power. But in every creature the essence differs from the existence, and is compared to it as potentiality is to act, as is evident from what has been already said (Q. 44, A. 1). Now the act to which the operative power is compared is operation. But in the angel to understand is not the same as to exist, nor is any operation in him, nor in any other created thing, the same as his existence. Hence the angel's essence is not his power of intelligence: nor is the essence of any creature its power of operation.

Reply Obj. 2: A simple form which is pure act cannot be the subject of accident, because subject is compared to accident as potentiality is to act. God alone is such a form: and of such is Boethius speaking there. But a simple form which is not its own existence, but is compared to it as potentiality is to act, can be the subject of accident; and especially of such accident as follows the species: for such accident belongs to the form—whereas an accident which belongs to the individual, and which does not belong to the whole species, results from the matter, which is the principle of individuation. And such a simple form is an angel.