Summa Th. I EN Qu.55 a.3
We now inquire into the knowledge of the angels with regard to the objects known by them. We shall treat of their knowledge, first, of immaterial things, secondly of things material. Under the first heading there are three points of inquiry:
(1) Does an angel know himself?
(2) Does one angel know another?
(3) Does the angel know God by his own natural principles?
Objection: 1. It would seem that an angel does not know himself. For Dionysius says that "the angels do not know their own powers" (Coel. Hier. vi). But, when the substance is known, the power is known. Therefore an angel does not know his own essence.
2. Further, an angel is a single substance, otherwise he would not act, since acts belong to single subsistences. But nothing single is intelligible. Therefore, since the angel possesses only knowledge which is intellectual, no angel can know himself.
3. Further, the intellect is moved by the intelligible object: because, as stated in De Anima iii, 4 understanding is a kind of passion. But nothing is moved by or is passive to itself; as appears in corporeal things. Therefore the angel cannot understand himself.
On the contrary Augustine says (Gn ad lit. ii) that "the angel knew himself when he was established, that is, enlightened by truth."
I answer that As is evident from what has been previously said (Question , Article ; Question , Article ), the object is on a different footing in an immanent, and in a transient, action. In a transient action the object or matter into which the action passes is something separate from the agent, as the thing heated is from what gave it heat, and the building from the builder; whereas in an immanent action, for the action to proceed, the object must be united with the agent; just as the sensible object must be in contact with sense, in order that sense may actually perceive. And the object which is united to a faculty bears the same relation to actions of this kind as does the form which is the principle of action in other agents: for, as heat is the formal principle of heating in the fire, so is the species of the thing seen the formal principle of sight to the eye.
It must, however, be borne in mind that this image of the object exists sometimes only potentially in the knowing faculty; and then there is only knowledge in potentiality; and in order that there may be actual knowledge, it is required that the faculty of knowledge be actuated by the species. But if it always actually possesses the species, it can thereby have actual knowledge without any preceding change or reception. From this it is evident that it is not of the nature of knower, as knowing, to be moved by the object, but as knowing in potentiality. Now, for the form to be the principle of the action, it makes no difference whether it be inherent in something else, or self-subsisting; because heat would give forth heat none the less if it were self-subsisting, than it does by inhering in something else. So therefore, if in the order of intelligible beings there be any subsisting intelligible form, it will understand itself. And since an angel is immaterial, he is a subsisting form; and, consequently, he is actually intelligible. Hence it follows that he understands himself by his form, which is his substance.
Reply to Objection: 1. That is the text of the old translation, which is amended in the new one, and runs thus: "furthermore they," that is to say the angels, "knew their own powers": instead of which the old translation read---"and furthermore they do not know their own powers." Although even the letter of the old translation might be kept in this respect, that the angels do not know their own power perfectly; according as it proceeds from the order of the Divine Wisdom, Which to the angels is incomprehensible.
2. We have no knowledge of single corporeal things, not because of their particularity, but on account of the matter, which is their principle of individuation. Accordingly, if there be any single things subsisting without matter, as the angels are, there is nothing to prevent them from being actually intelligible.
3. It belongs to the intellect, in so far as if is in potentiality, to be moved and to be passive. Hence this does not happen in the angelic intellect, especially as regards the fact that he understands himself. Besides the action of the intellect is not of the same nature as the action found in corporeal things, which passes into some other matter.
Objection: 1. It would seem that one angel does not know another. For the Philosopher says (De Anima iii, text. 4), that if the human intellect were to have in itself any one of the sensible things, then such a nature existing within it would prevent it from apprehending external things; as likewise, if the pupil of the eye were colored with some particular color, it could not see every color. But as the human intellect is disposed for understanding corporeal things, so is the angelic mind for understanding immaterial things. Therefore, since the angelic intellect has within itself some one determinate nature from the number of such natures, it would seem that it cannot understand other natures.
2. Further, it is stated in De Causis that "every intelligence knows what is above it, in so far as it is caused by it; and what is beneath it, in so far as it is its cause." But one angel is not the cause of another. Therefore one angel does not know another.
3. Further, one angel cannot be known to another angel by the essence of the one knowing; because all knowledge is effected by way of a likeness. But the essence of the angel knowing is not like the essence of the angel known, except generically; as is clear from what has been said before (Question , Article ; Question , Article , ad 3). Hence, it follows that one angel would not have a particular knowledge of another, but only a general knowledge. In like manner it cannot be said that one angel knows another by the essence of the angel known; because that whereby the intellect understands is something within the intellect; whereas the Trinity alone can penetrate the mind. Again, it cannot be said that one angel knows the other by a species; because that species would not differ from the angel understood, since each is immaterial. Therefore in no way does it appear that one angel can understand another.
4. Further, if one angel did understand another, this would be either by an innate species; and so it would follow that, if God were now to create another angel, such an angel could not be known by the existing angels; or else he would have to be known by a species drawn from things; and so it would follow that the higher angels could not know the lower, from whom they receive nothing. Therefore in no way does it seem that one angel knows another.
On the contrary We read in De Causis that "every intelligence knows the things which are not corrupted."
I answer that As Augustine says (Gn ad lit. lit. ii), such things as pre-existed from eternity in the Word of God, came forth from Him in two ways: first, into the angelic mind; and secondly, so as to subsist in their own natures. They proceeded into the angelic mind in such a way, that God impressed upon the angelic mind the images of the things which He produced in their own natural being. Now in the Word of God from eternity there existed not only the forms of corporeal things, but likewise the forms of all spiritual creatures. So in every one of these spiritual creatures, the forms of all things, both corporeal and spiritual, were impressed by the Word of God; yet so that in every angel there was impressed the form of his own species according to both its natural and its intelligible condition, so that he should subsist in the nature of his species, and understand himself by it; while the forms of other spiritual and corporeal natures were impressed in him only according to their intelligible natures, so that by such impressed species he might know corporeal and spiritual creatures.
Reply to Objection: 1. The spiritual natures of the angels are distinguished from one another in a certain order, as was already observed (Question , Article , ad 1,2). So the nature of an angel does not hinder him from knowing the other angelic natures, since both the higher and lower bear affinity to his nature, the only difference being according to their various degrees of perfection.
2. The nature of cause and effect does not lead one angel to know another, except on account of likeness, so far as cause and effect are alike. Therefore if likeness without causality be admitted in the angels, this will suffice for one to know another.
3. One angel knows another by the species of such angel existing in his intellect, which differs from the angel whose image it is, not according to material and immaterial nature, but according to natural and intentional existence. The angel is himself a subsisting form in his natural being; but his species in the intellect of another angel is not so, for there it possesses only an intelligible existence. As the form of color on the wall has a natural existence; but, in the deferent medium, it has only intentional existence.
4. God made every creature proportionate to the universe which He determined to make. Therefore had God resolved to make more angels or more natures of things, He would have impressed more intelligible species in the angelic minds; as a builder who, if he had intended to build a larger house, would have made larger foundations. Hence, for God to add a new creature to the universe, means that He would add a new intelligible species to an angel.
Objection: 1. It would seem that the angels cannot know God by their natural principles. For Dionysius says (Div. Nom. i) that God "by His incomprehensible might is placed above all heavenly minds." Afterwards he adds that, "since He is above all substances, He is remote from all knowledge."
2. Further, God is infinitely above the intellect of an angel. But what is infinitely beyond cannot be reached. Therefore it appears that an angel cannot know God by his natural principles.
3. Further, it is written (1Co 13,12): "We see now through a glass in a dark manner; but then face to face." From this it appears that there is a twofold knowledge of God; the one, whereby He is seen in His essence, according to which He is said to be seen face to face; the other whereby He is seen in the mirror of creatures. As was already shown (Question , Article ), an angel cannot have the former knowledge by his natural principles. Nor does vision through a mirror belong to the angels, since they do not derive their knowledge of God from sensible things, as Dionysius observes (Div. Nom. vii). Therefore the angels cannot know God by their natural powers.
On the contrary The angels are mightier in knowledge than men. Yet men can know God through their natural principles; according to Rm 1,19: "what is known of God is manifest in them." Therefore much more so can the angels.
I answer that The angels can have some knowledge of God by their own principles. In evidence whereof it must be borne in mind that a thing is known in three ways: first, by the presence of its essence in the knower, as light can be seen in the eye; and so we have said that an angel knows himself---secondly, by the presence of its similitude in the power which knows it, as a stone is seen by the eye from its image being in the eye---thirdly, when the image of the object known is not drawn directly from the object itself, but from something else in which it is made to appear, as when we behold a man in a mirror.
To the first-named class that knowledge of God is likened by which He is seen through His essence; and knowledge such as this cannot accrue to any creature from its natural principles, as was said above (Question , Article ). The third class comprises the knowledge whereby we know God while we are on earth, by His likeness reflected in creatures, according to Rm 1,20: "The invisible things of God are clearly seen, being understood by the things that are made." Hence, too, we are said to see God in a mirror. But the knowledge, whereby according to his natural principles the angel knows God, stands midway between these two; and is likened to that knowledge whereby a thing is seen through the species abstracted from it. For since God's image is impressed on the very nature of the angel in his essence, the angel knows God in as much as he is the image of God. Yet he does not behold God's essence; because no created likeness is sufficient to represent the Divine essence. Such knowledge then approaches rather to the specular kind; because the angelic nature is itself a kind of mirror representing the Divine image.
Reply to Objection: 1. Dionysius is speaking of the knowledge of comprehension, as his words expressly state. In this way God is not known by any created intellect.
2. Since an angel's intellect and essence are infinitely remote from God, it follows that he cannot comprehend Him; nor can he see God's essence through his own nature. Yet it does not follow on that account that he can have no knowledge of Him at all: because, as God is infinitely remote from the angel, so the knowledge which God has of Himself is infinitely above the knowledge which an angel has of Him.
3. The knowledge which an angel has of God is midway between these two kinds of knowledge; nevertheless it approaches more to one of them, as was said above.
We next investigate the material objects which are known by the angels. Under this heading there are five points of inquiry:
(1) Whether the angels know the natures of material things?
(2) Whether they know single things?
(3) Whether they know the future?
(4) Whether they know secret thoughts?
(5) Whether they know all mysteries of grace?
Objection: 1. It would seem that the angels do not know material things. For the object understood is the perfection of him who understands it. But material things cannot be the perfections of angels, since they are beneath them. Therefore the angels do not know material things.
2. Further, intellectual vision is only of such things as exist within the soul by their essence, as is said in the gloss [*On 2Co 12,2, taken from Augustine (Gn ad lit. xii. 28)]. But the material things cannot enter by their essence into man's soul, nor into the angel's mind. Therefore they cannot be known by intellectual vision, but only by imaginary vision, whereby the images of bodies are apprehended, and by sensible vision, which regards bodies in themselves. Now there is neither imaginary nor sensible vision in the angels, but only intellectual. Therefore the angels cannot know material things.
3. Further, material things are not actually intelligible, but are knowable by apprehension of sense and of imagination, which does not exist in angels. Therefore angels do not know material things.
On the contrary Whatever the lower power can do, the higher can do likewise. But man's intellect, which in the order of nature is inferior to the angel's, can know material things. Therefore much more can the mind of an angel.
I answer that The established order of things is for the higher beings to be more perfect than the lower; and for whatever is contained deficiently, partially, and in manifold manner in the lower beings, to be contained in the higher eminently, and in a certain degree of fulness and simplicity. Therefore, in God, as in the highest source of things, all things pre-exist supersubstantially in respect of His simple Being itself, as Dionysius says (Div. Nom. 1). But among other creatures the angels are nearest to God, and resemble Him most; hence they share more fully and more perfectly in the Divine goodness, as Dionysius says (Coel. Hier. iv). Consequently, all material things pre-exist in the angels more simply and less materially even than in themselves, yet in a more manifold manner and less perfectly than in God.
Now whatever exists in any subject, is contained in it after the manner of such subject. But the angels are intellectual beings of their own nature. Therefore, as God knows material things by His essence, so do the angels know them, forasmuch as they are in the angels by their intelligible species.
Reply to Objection: 1. The thing understood is the perfection of the one who understands, by reason of the intelligible species which he has in his intellect. And thus the intelligible species which are in the intellect of an angel are perfections and acts in regard to that intellect.
2. Sense does not apprehend the essences of things, but only their outward accidents. In like manner neither does the imagination; for it apprehends only the images of bodies. The intellect alone apprehends the essences of things. Hence it is said (De Anima iii, text. 26) that the object of the intellect is "what a thing is," regarding which it does not err; as neither does sense regarding its proper sensible object. So therefore the essences of material things are in the intellect of man and angels, as the thing understood is in him who understands, and not according to their real natures. But some things are in an intellect or in the soul according to both natures; and in either case there is intellectual vision.
3. If an angel were to draw his knowledge of material things from the material things themselves, he would require to make them actually intelligible by a process of abstraction. But he does not derive his knowledge of them from the material things themselves; he has knowledge of material things by actually intelligible species of things, which species are connatural to him; just as our intellect has, by species which it makes intelligible by abstraction.
Objection: 1. It would seem that angels do not know singulars. For the Philosopher says (Poster. i, text. 22): "The sense has for its object singulars, but the intellect, universals." Now, in the angels there is no power of understanding save the intellectual power, as is evident from what was said above (Question , Article ). Consequently they do not know singulars.
2. Further, all knowledge comes about by some assimilation of the knower to the object known. But it is not possible for any assimilation to exist between an angel and a singular object, in so far as it is singular; because, as was observed above (Question , Article ), an angel is immaterial, while matter is the principle of singularity. Therefore the angel cannot know singulars.
3. Further, if an angel does know singulars, it is either by singular or by universal species. It is not by singular species; because in this way he would require to have an infinite number of species. Nor is it by universal species; since the universal is not the sufficient principle for knowing the singular as such, because singular things are not known in the universal except potentially. Therefore the angel does not know singulars.
On the contrary No one can guard what he does not know. But angels guard individual men, according to Ps 90,11: "He hath given His angels charge over Thee." Consequently the angels know singulars.
I answer that Some have denied to the angels all knowledge of singulars. In the first place this derogates from the Catholic faith, which asserts that these lower things are administered by angels, according to He 1,14: "They are all ministering spirits." Now, if they had no knowledge of singulars, they could exercise no provision over what is going on in this world; since acts belong to individuals: and this is against the text of Qo 5,5: "Say not before the angel: There is no providence." Secondly, it is also contrary to the teachings of philosophy, according to which the angels are stated to be the movers of the heavenly spheres, and to move them according to their knowledge and will.
Consequently others have said that the angel possesses knowledge of singulars, but in their universal causes, to which all particular effects are reduced; as if the astronomer were to foretell a coming eclipse from the dispositions of the movements of the heavens. This opinion does not escape the aforesaid implications; because, to know a singular, merely in its universal causes, is not to know it as singular, that is, as it exists here and now. The astronomer, knowing from computation of the heavenly movements that an eclipse is about to happen, knows it in the universal; yet he does not know it as taking place now, except by the senses. But administration, providence and movement are of singulars, as they are here and now existing.
Therefore, it must be said differently, that, as man by his various powers of knowledge knows all classes of things, apprehending universals and immaterial things by his intellect, and things singular and corporeal by the senses, so an angel knows both by his one mental power. For the order of things runs in this way, that the higher a thing is, so much the more is its power united and far-reaching: thus in man himself it is manifest that the common sense which is higher than the proper sense, although it is but one faculty, knows everything apprehended by the five outward senses, and some other things which no outer sense knows; for example, the difference between white and sweet. The same is to be observed in other cases. Accordingly, since an angel is above man in the order of nature, it is unreasonable to say that a man knows by any one of his powers something which an angel by his one faculty of knowledge, namely, the intellect, does not know. Hence Aristotle pronounces it ridiculous to say that a discord, which is known to us, should be unknown to God (De Anima i, text. 80; Metaph. text. 15).
The manner in which an angel knows singular things can be considered from this, that, as things proceed from God in order that they may subsist in their own natures, so likewise they proceed in order that they may exist in the angelic mind. Now it is clear that there comes forth from God not only whatever belongs to their universal nature, but likewise all that goes to make up their principles of individuation; since He is the cause of the entire substance of the thing, as to both its matter and its form. And for as much as He causes, does He know; for His knowledge is the cause of a thing, as was shown above (Question , Article ). Therefore as by His essence, by which He causes all things, God is the likeness of all things, and knows all things, not only as to their universal natures, but also as to their singularity; so through the species imparted to them do the angels know things, not only as to their universal nature, but likewise in their individual conditions, in so far as they are the manifold representations of that one simple essence.
Reply to Objection: 1. The Philosopher is speaking of our intellect, which apprehends only by a process of abstraction; and by such abstraction from material conditions the thing abstracted becomes a universal. Such a manner of understanding is not in keeping with the nature of the angels, as was said above (Question , Article , Article  ad 1), and consequently there is no comparison.
2. It is not according to their nature that the angels are likened to material things, as one thing resembles another by agreement in genus, species, or accident; but as the higher bears resemblance to the lower, as the sun does to fire. Even in this way there is in God a resemblance of all things, as to both matter and form, in so far as there pre-exists in Him as in its cause whatever is to be found in things. For the same reason, the species in the angel's intellect, which are images drawn from the Divine essence, are the images of things not only as to their form, but also as to their matter.
3. Angels know singulars by universal forms, which nevertheless are the images of things both as to their universal, and as to their individuating principles. How many things can be known by the same species, has been already stated above (Question , Article , ad 3).
Objection: 1. It would seem that the angels know future events. For angels are mightier in knowledge than men. But some men know many future events. Therefore much more do the angels.
2. Further, the present and the future are differences of time. But the angel's intellect is above time; because, as is said in De Causis, "an intelligence keeps pace with eternity," that is, aeviternity. Therefore, to the angel's mind, past and future are not different, but he knows each indifferently.
3. Further, the angel does not understand by species derived from things, but by innate universal species. But universal species refer equally to present, past, and future. Therefore it appears that the angels know indifferently things past, present, and future.
4. Further, as a thing is spoken of as distant by reason of time, so is it by reason of place. But angels know things which are distant according to place. Therefore they likewise know things distant according to future time.
On the contrary Whatever is the exclusive sign of the Divinity, does not belong to the angels. But to know future events is the exclusive sign of the Divinity, according to Is 41,23: "Show the things that are to come hereafter, and we shall know that ye are gods." Therefore the angels do not know future events.
I answer that The future can be known in two ways. First, it can be known in its cause. And thus, future events which proceed necessarily from their causes, are known with sure knowledge; as that the sun will rise tomorrow. But events which proceed from their causes in the majority of cases, are not known for certain, but conjecturally; thus the doctor knows beforehand the health of the patient. This manner of knowing future events exists in the angels, and by so much the more than it does in us, as they understand the causes of things both more universally and more perfectly; thus doctors who penetrate more deeply into the causes of an ailment can pronounce a surer verdict on the future issue thereof. But events which proceed from their causes in the minority of cases are quite unknown; such as casual and chance events.
In another way future events are known in themselves. To know the future in this way belongs to God alone; and not merely to know those events which happen of necessity, or in the majority of cases, but even casual and chance events; for God sees all things in His eternity, which, being simple, is present to all time, and embraces all time. And therefore God's one glance is cast over all things which happen in all time as present before Him; and He beholds all things as they are in themselves, as was said before when dealing with God's knowledge (Question , Article ). But the mind of an angel, and every created intellect, fall far short of God's eternity; hence the future as it is in itself cannot be known by any created intellect.
Reply to Objection: 1. Men cannot know future things except in their causes, or by God's revelation. The angels know the future in the same way, but much more distinctly.
2. Although the angel's intellect is above that time according to which corporeal movements are reckoned, yet there is a time in his mind according to the succession of intelligible concepts; of which Augustine says (Gn ad lit. viii) that "God moves the spiritual creature according to time." And thus, since there is succession in the angel's intellect, not all things that happen through all time, are present to the angelic mind.
3. Although the species in the intellect of an angel, in so far as they are species, refer equally to things present, past, and future; nevertheless the present, past, and future; nevertheless the present, past, and future do not bear the same relations to the species. Present things have a nature according to which they resemble the species in the mind of an angel: and so they can be known thereby. Things which are yet to come have not yet a nature whereby they are likened to such species; consequently, they cannot be known by those species.
4. Things distant according to place are already existing in nature; and share in some species, whose image is in the angel; whereas this is not true of future things, as has been stated. Consequently there is no comparison.
Objection: 1. It would seem that the angels know secret thoughts. For Gregory (Moral. xviii), explaining Jb 28,17: "Gold or crystal cannot equal it," says that "then," namely in the bliss of those rising from the dead, "one shall be as evident to another as he is to himself, and when once the mind of each is seen, his conscience will at the same time be penetrated." But those who rise shall be like the angels, as is stated (Mt 22,30). Therefore an angel can see what is in another's conscience.
2. Further, intelligible species bear the same relation to the intellect as shapes do to bodies. But when the body is seen its shape is seen. Therefore, when an intellectual substance is seen, the intelligible species within it is also seen. Consequently, when one angel beholds another, or even a soul, it seems that he can see the thoughts of both.
3. Further, the ideas of our intellect resemble the angel more than do the images in our imagination; because the former are actually understood, while the latter are understood only potentially. But the images in our imagination can be known by an angel as corporeal things are known: because the imagination is a corporeal faculty. Therefore it seems that an angel can know the thoughts of the intellect.
On the contrary What is proper to God does not belong to the angels. But it is proper to God to read the secrets of hearts, according to Jr 17,9: "The heart is perverse above all things, and unsearchable; who can know it? I am the Lord, Who search the heart." Therefore angels do not know the secrets of hearts.
I answer that A secret thought can be known in two ways: first, in its effect. In this way it can be known not only by an angel, but also by man; and with so much the greater subtlety according as the effect is the more hidden. For thought is sometimes discovered not merely by outward act, but also by change of countenance; and doctors can tell some passions of the soul by the mere pulse. Much more then can angels, or even demons, the more deeply they penetrate those occult bodily modifications. Hence Augustine says (De divin. daemon.) that demons "sometimes with the greatest faculty learn man's dispositions, not only when expressed by speech, but even when conceived in thought, when the soul expresses them by certain signs in the body"; although (Retract. ii, 30) he says "it cannot be asserted how this is done."
In another way thoughts can be known as they are in the mind, and affections as they are in the will: and thus God alone can know the thoughts of hearts and affections of wills. The reason of this is, because the rational creature is subject to God only, and He alone can work in it Who is its principal object and last end: this will be developed later (Question , Article ; Question , Article ). Consequently all that is in the will, and all things that depend only on the will, are known to God alone. Now it is evident that it depends entirely on the will for anyone actually to consider anything; because a man who has a habit of knowledge, or any intelligible species, uses them at will. Hence the Apostle says (1Co 2,11): "For what man knoweth the things of a man, but the spirit of a man that is in him?"
Reply to Objection: 1. In the present life one man's thought is not known by another owing to a twofold hindrance; namely, on account of the grossness of the body, and because the will shuts up its secrets. The first obstacle will be removed at the Resurrection, and does not exist at all in the angels; while the second will remain, and is in the angels now. Nevertheless the brightness of the body will show forth the quality of the soul; as to its amount of grace and of glory. In this way one will be able to see the mind of another.
2. Although one angel sees the intelligible species of another, by the fact that the species are proportioned to the rank of these substances according to greater or lesser universality, yet it does not follow that one knows how far another makes use of them by actual consideration.
3. The appetite of the brute does not control its act, but follows the impression of some other corporeal or spiritual cause. Since, therefore, the angels know corporeal things and their dispositions, they can thereby know what is passing in the appetite or in the imaginative apprehension of the brute beasts, and even of man, in so far as the sensitive appetite sometimes, through following some bodily impression, influences his conduct, as always happens in brutes. Yet the angels do not necessarily know the movement of the sensitive appetite and the imaginative apprehension of man in so far as these are moved by the will and reason; because, even the lower part of the soul has some share of reason, as obeying its ruler, as is said in Ethics iii, 12. But it does not follow that, if the angel knows what is passing through man's sensitive appetite or imagination, he knows what is in the thought or will: because the intellect or will is not subject to the sensitive appetite or the imagination, but can make various uses of them.
Summa Th. I EN Qu.55 a.3