Summa Theologica, by St. Thomas Aquinas, [1947], at sacred-texts.com
We next inquire about the angels in comparison with corporeal things; and in the first place about their comparison with bodies; secondly, of the angels in comparison with corporeal places; and, thirdly, of their comparison with local movement.
Under the first heading there are three points of inquiry:
(1) Whether angels have bodies naturally united to them?
(2) Whether they assume bodies?
(3) Whether they exercise functions of life in the bodies assumed?
Objection 1: It would seem that angels have bodies naturally united to them. For Origen says (Peri Archon i): "It is God's attribute alone---that is, it belongs to the Father, the Son, and the Holy Ghost, as a property of nature, that He is understood to exist without any material substance and without any companionship of corporeal addition." Bernard likewise says (Hom. vi. super Cant.): "Let us assign incorporeity to God alone even as we do immortality, whose nature alone, neither for its own sake nor on account of anything else, needs the help of any corporeal organ. But it is clear that every created spirit needs corporeal substance." Augustine also says (Gen. ad lit. iii): "The demons are called animals of the atmosphere because their nature is akin to that of aerial bodies." But the nature of demons and angels is the same. Therefore angels have bodies naturally united to them.
Objection 2: Further, Gregory (Hom. x in Ev.) calls an angel a rational animal. But every animal is composed of body and soul. Therefore angels have bodies naturally united to them.
Objection 3: Further, life is more perfect in the angels than in souls. But the soul not only lives, but gives life to the body. Therefore the angels animate bodies which are naturally united to them.
On the contrary, Dionysius says (Div. Nom. iv) that "the angels are understood to be incorporeal."
I answer that, The angels have not bodies naturally united to them. For whatever belongs to any nature as an accident is not found universally in that nature; thus, for instance, to have wings, because it is not of the essence of an animal, does not belong to every animal. Now since to understand is not the act of a body, nor of any corporeal energy, as will be shown later (Q[75], A[2]), it follows that to have a body united to it is not of the nature of an intellectual substance, as such; but it is accidental to some intellectual substance on account of something else. Even so it belongs to the human soul to be united to a body, because it is imperfect and exists potentially in the genus of intellectual substances, not having the fulness of knowledge in its own nature, but acquiring it from sensible things through the bodily senses, as will be explained later on (Q[84], A[6]; Q[89], A[1]). Now whenever we find something imperfect in any genus we must presuppose something perfect in that genus. Therefore in the intellectual nature there are some perfectly intellectual substances, which do not need to acquire knowledge from sensible things. Consequently not all intellectual substances are united to bodies; but some are quite separated from bodies, and these we call angels.
Reply to Objection 1: As was said above (Q[50], A[1]) it was the opinion of some that every being is a body; and consequently some seem to have thought that there were no incorporeal substances existing except as united to bodies; so much so that some even held that God was the soul of the world, as Augustine tells us (De Civ. Dei vii). As this is contrary to Catholic Faith, which asserts that God is exalted above all things, according to Ps. 8:2: "Thy magnificence is exalted beyond the heavens"; Origen, while refusing to say such a thing of God, followed the above opinion of others regarding the other substances; being deceived here as he was also in many other points, by following the opinions of the ancient philosophers. Bernard's expression can be explained, that the created spirit needs some bodily instrument, which is not naturally united to it, but assumed for some purpose, as will be explained (A[2]). Augustine speaks, not as asserting the fact, but merely using the opinion of the Platonists, who maintained that there are some aerial animals, which they termed demons.
Reply to Objection 2: Gregory calls the angel a rational animal metaphorically, on account of the likeness to the rational nature.
Reply to Objection 3: To give life effectively is a perfection simply speaking; hence it belongs to God, as is said (1 Kings 2:6): "The Lord killeth, and maketh alive." But to give life formally belongs to a substance which is part of some nature, and which has not within itself the full nature of the species. Hence an intellectual substance which is not united to a body is more perfect than one which is united to a body.
Objection 1: It would seem that angels do not assume bodies. For there is nothing superfluous in the work of an angel, as there is nothing of the kind in the work of nature. But it would be superfluous for the angels to assume bodies, because an angel has no need for a body, since his own power exceeds all bodily power. Therefore an angel does not assume a body.
Objection 2: Further, every assumption is terminated in some union; because to assume implies a taking to oneself [ad se sumere]. But a body is not united to an angel as to a form, as stated (A[1]); while in so far as it is united to the angel as to a mover, it is not said to be assumed, otherwise it would follow that all bodies moved by the angels are assumed by them. Therefore the angels do not assume bodies.
Objection 3: Further, angels do not assume bodies from the earth or water, or they could not suddenly disappear; nor again from fire, otherwise they would burn whatever things they touched; nor again from air, because air is without shape or color. Therefore the angels do not assume bodies.
On the contrary, Augustine says (De Civ. Dei xvi) that angels appeared to Abraham under assumed bodies.
I answer that, Some have maintained that the angels never assume bodies, but that all that we read in Scripture of apparitions of angels happened in prophetic vision---that is, according to imagination. But this is contrary to the intent of Scripture; for whatever is beheld in imaginary vision is only in the beholder's imagination, and consequently is not seen by everybody. Yet Divine Scripture from time to time introduces angels so apparent as to be seen commonly by all; just as the angels who appeared to Abraham were seen by him and by his whole family, by Lot, and by the citizens of Sodom; in like manner the angel who appeared to Tobias was seen by all present. From all this it is clearly shown that such apparitions were beheld by bodily vision, whereby the object seen exists outside the person beholding it, and can accordingly be seen by all. Now by such a vision only a body can be beheld. Consequently, since the angels are not bodies, nor have they bodies naturally united with them, as is clear from what has been said (A[1]; Q[50], A[1]), it follows that they sometimes assume bodies.
Reply to Objection 1: Angels need an assumed body, not for themselves, but on our account; that by conversing familiarly with men they may give evidence of that intellectual companionship which men expect to have with them in the life to come. Moreover that angels assumed bodies under the Old Law was a figurative indication that the Word of God would take a human body; because all the apparitions in the Old Testament were ordained to that one whereby the Son of God appeared in the flesh.
Reply to Objection 2: The body assumed is united to the angel not as its form, nor merely as its mover, but as its mover represented by the assumed movable body. For as in the Sacred Scripture the properties of intelligible things are set forth by the likenesses of things sensible, in the same way by Divine power sensible bodies are so fashioned by angels as fittingly to represent the intelligible properties of an angel. And this is what we mean by an angel assuming a body.
Reply to Objection 3: Although air as long as it is in a state of rarefaction has neither shape nor color, yet when condensed it can both be shaped and colored as appears in the clouds. Even so the angels assume bodies of air, condensing it by the Divine power in so far as is needful for forming the assumed body.
Objection 1: It would seem that the angels exercise functions of life in assumed bodies. For pretence is unbecoming in angels of truth. But it would be pretence if the body assumed by them, which seems to live and to exercise vital functions, did not possess these functions. Therefore the angels exercise functions of life in the assumed body.
Objection 2: Further, in the works of the angels there is nothing without a purpose. But eyes, nostrils, and the other instruments of the senses, would be fashioned without a purpose in the body assumed by the angel, if he perceived nothing by their means. Consequently, the angel perceives by the assumed body; and this is the most special function of life.
Objection 3: Further, to move hither and thither is one of the functions of life, as the Philosopher says (De Anima ii). But the angels are manifestly seen to move in their assumed bodies. For it was said (Gn. 18:16) that "Abraham walked with" the angels, who had appeared to him, "bringing them on the way"; and when Tobias said to the angel (Tob. 5:7, 8): "Knowest thou the way that leadeth to the city of Medes?" he answered: "I know it; and I have often walked through all the ways thereof." Therefore the angels often exercise functions of life in assumed bodies.
Objection 4: Further, speech is the function of a living subject, for it is produced by the voice, while the voice itself is a sound conveyed from the mouth. But it is evident from many passages of Sacred Scripture that angels spoke in assumed bodies. Therefore in their assumed bodies they exercise functions of life.
Objection 5: Further, eating is a purely animal function. Hence the Lord after His Resurrection ate with His disciples in proof of having resumed life (Lk. 24). Now when angels appeared in their assumed bodies they ate, and Abraham offered them food, after having previously adored them as God (Gn. 18). Therefore the angels exercise functions of life in assumed bodies.
Objection 6: Further, to beget offspring is a vital act. But this has befallen the angels in their assumed bodies; for it is related: "After the sons of God went in to the daughters of men, and they brought forth children, these are the mighty men of old, men of renown" (Gn. 6:4). Consequently the angels exercised vital functions in their assumed bodies.
On the contrary, The bodies assumed by angels have no life, as was stated in the previous article (ad 3). Therefore they cannot exercise functions of life through assumed bodies.
I answer that, Some functions of living subjects have something in common with other operations; just as speech, which is the function of a living creature, agrees with other sounds of inanimate things, in so far as it is sound; and walking agrees with other movements, in so far as it is movement. Consequently vital functions can be performed in assumed bodies by the angels, as to that which is common in such operations; but not as to that which is special to living subjects; because, according to the Philosopher (De Somn. et Vig. i), "that which has the faculty has the action." Hence nothing can have a function of life except what has life, which is the potential principle of such action.
Reply to Objection 1: As it is in no wise contrary to truth for intelligible things to be set forth in Scripture under sensible figures, since it is not said for the purpose of maintaining that intelligible things are sensible, but in order that properties of intelligible things may be understood according to similitude through sensible figures; so it is not contrary to the truth of the holy angels that through their assumed bodies they appear to be living men, although they are really not. For the bodies are assumed merely for this purpose, that the spiritual properties and works of the angels may be manifested by the properties of man and of his works. This could not so fittingly be done if they were to assume true men; because the properties of such men would lead us to men, and not to angels.
Reply to Objection 2: Sensation is entirely a vital function. Consequently it can in no way be said that the angels perceive through the organs of their assumed bodies. Yet such bodies are not fashioned in vain; for they are not fashioned for the purpose of sensation through them, but to this end, that by such bodily organs the spiritual powers of the angels may be made manifest; just as by the eye the power of the angel's knowledge is pointed out, and other powers by the other members, as Dionysius teaches (Coel. Hier.).
Reply to Objection 3: Movement coming from a united mover is a proper function of life; but the bodies assumed by the angels are not thus moved, since the angels are not their forms. Yet the angels are moved accidentally, when such bodies are moved, since they are in them as movers are in the moved; and they are here in such a way as not to be elsewhere which cannot be said of God. Accordingly, although God is not moved when the things are moved in which He exists, since He is everywhere; yet the angels are moved accidentally according to the movement of the bodies assumed. But they are not moved according to the movement of the heavenly bodies, even though they be in them as the movers in the thing moved, because the heavenly bodies do not change place in their entirety; nor for the spirit which moves the world is there any fixed locality according to any restricted part of the world's substance, which now is in the east, and now in the west, but according to a fixed quarter; because "the moving energy is always in the east," as stated in Phys. viii, text 84.
Reply to Objection 4: Properly speaking, the angels do not talk through their assumed bodies; yet there is a semblance of speech, in so far as they fashion sounds in the air like to human voices.
Reply to Objection 5: Properly speaking, the angels cannot be said to eat, because eating involves the taking of food convertible into the substance of the eater.
Although after the Resurrection food was not converted into the substance of Christ's body, but resolved into pre-existing matter; nevertheless Christ had a body of such a true nature that food could be changed into it; hence it was a true eating. But the food taken by angels was neither changed into the assumed body, nor was the body of such a nature that food could be changed into it; consequently, it was not a true eating, but figurative of spiritual eating. This is what the angel said to Tobias: "When I was with you, I seemed indeed to eat and to drink; but I use an invisible meat and drink" (Tob. 12:19).
Abraham offered them food, deeming them to be men, in whom, nevertheless, he worshipped God, as God is wont to be in the prophets, as Augustine says (De Civ. Dei xvi).
Reply to Objection 6: As Augustine says (De Civ. Dei xv): "Many persons affirm that they have had the experience, or have heard from such as have experienced it, that the Satyrs and Fauns, whom the common folk call incubi, have often presented themselves before women, and have sought and procured intercourse with them. Hence it is folly to deny it. But God's holy angels could not fall in such fashion before the deluge. Hence by the sons of God are to be understood the sons of Seth, who were good; while by the daughters of men the Scripture designates those who sprang from the race of Cain. Nor is it to be wondered at that giants should be born of them; for they were not all giants, albeit there were many more before than after the deluge." Still if some are occasionally begotten from demons, it is not from the seed of such demons, nor from their assumed bodies, but from the seed of men taken for the purpose; as when the demon assumes first the form of a woman, and afterwards of a man; just as they take the seed of other things for other generating purposes, as Augustine says (De Trin. iii), so that the person born is not the child of a demon, but of a man.