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Home > Summa Theologiae > First Part > Question 42

Question 42. Equality and likeness among the divine persons

  1. Is there equality among the divine persons?
  2. Is the person who proceeds equal to the one from Whom He proceeds in eternity?
  3. Is there any order among the divine persons?
  4. Are the divine persons equal in greatness?
  5. Is the one divine person in another?
  6. Are they equal in power?

Article 1. Whether there is equality in God?

Objection 1. It would seem that equality is not becoming to the divine persons. For equality is in relation to things which are one in quantity as the Philosopher says (Metaph. v, text 20). But in the divine persons there is no quantity, neither continuous intrinsic quantity, which we call size, nor continuous extrinsic quantity, which we call place and time. Nor can there be equality by reason of discrete quantity, because two persons are more than one. Therefore equality is not becoming to the divine persons.

Objection 2. Further, the divine persons are of one essence, as we have said (I:39:2. Now essence is signified by way of form. But agreement in form makes things to be alike, not to be equal. Therefore, we may speak of likeness in the divine persons, but not of equality.

Objection 3. Further, things wherein there is to be found equality, are equal to one another, for equality is reciprocal. But the divine persons cannot be said to be equal to one another. For as Augustine says (De Trin. vi, 10): "If an image answers perfectly to that whereof it is the image, it may be said to be equal to it; but that which it represents cannot be said to be equal to the image." But the Son is the image of the Father; and so the Father is not equal to the Son. Therefore equality is not to be found among the divine persons.

Objection 4. Further, equality is a relation. But no relation is common to the three persons; for the persons are distinct by reason of the relations. Therefore equality is not becoming to the divine persons.

On the contrary, Athanasius says that "the three persons are co-eternal and co-equal to one another."

I answer that, We must needs admit equality among the divine persons. For, according to the Philosopher (Metaph. x, text 15,16, 17), equality signifies the negation of greater or less. Now we cannot admit anything greater or less in the divine persons; for as Boethius says (De Trin. i): "They must needs admit a difference [namely, of Godhead] who speak of either increase or decrease, as the Arians do, who sunder the Trinity by distinguishing degrees as of numbers, thus involving a plurality." Now the reason of this is that unequal things cannot have the same quantity. But quantity, in God, is nothing else than His essence. Wherefore it follows, that if there were any inequality in the divine persons, they would not have the same essence; and thus the three persons would not be one God; which is impossible. We must therefore admit equality among the divine persons.

Reply to Objection 1. Quantity is twofold. There is quantity of "bulk" or dimensive quantity, which is to be found only in corporeal things, and has, therefore, no place in God. There is also quantity of "virtue," which is measured according to the perfection of some nature or form: to this sort of quantity we allude when we speak of something as being more, or less, hot; forasmuch as it is more or less, perfect in heat. Now this virtual quantity is measured firstly by its source—that is, by the perfection of that form or nature: such is the greatness of spiritual things, just as we speak of great heat on account of its intensity and perfection. And so Augustine says (De Trin. vi, 18) that "in things which are great, but not in bulk, to be greater is to be better," for the more perfect a thing is the better it is.

Secondly, virtual quantity is measured by the effects of the form. Now the first effect of form is being, for everything has being by reason of its form. The second effect is operation, for every agent acts through its form. Consequently virtual quantity is measured both in regard to being and in regard to action: in regard to being, forasmuch as things of a more perfect nature are of longer duration; and in regard to action, forasmuch as things of a more perfect nature are more powerful to act. And so as Augustine (Fulgentius, De Fide ad Petrum i) says: "We understand equality to be in the Father, Son and Holy Ghost, inasmuch as no one of them either precedes in eternity, or excels in greatness, or surpasses in power."

Reply to Objection 2. Where we have equality in respect of virtual quantity, equality includes likeness and something besides, because it excludes excess. For whatever things have a common form may be said to be alike, even if they do not participate in that form equally, just as the air may be said to be like fire in heat; but they cannot be said to be equal if one participates in the form more perfectly than another. And because not only is the same nature in both Father and Son, but also is it in both in perfect equality, therefore we say not only that the Son is like to the Father, in order to exclude the error of Eunomius, but also that He is equal to the Father to exclude the error of Arius.

Reply to Objection 3. Equality and likeness in God may be designated in two ways—namely, by nouns and by verbs. When designated by nouns, equality in the divine persons is mutual, and so is likeness; for the Son is equal and like to the Father, and conversely. This is because the divine essence is not more the Father's than the Son's. Wherefore, just as the Son has the greatness of the Father, and is therefore equal to the Father, so the Father has the greatness of the Son, and is therefore equal to the Son. But in reference to creatures, Dionysius says (Div. Nom. ix): "Equality and likeness are not mutual." For effects are said to be like their causes, inasmuch as they have the form of their causes; but not conversely, for the form is principally in the cause, and secondarily in the effect.

But verbs signify equality with movement. And although movement is not in God, there is something that receives. Since, therefore, the Son receives from the Father, this, namely, that He is equal to the Father, and not conversely, for this reason we say that the Son is equalled to the Father, but not conversely.

Reply to Objection 4. In the divine persons there is nothing for us to consider but the essence which they have in common and the relations in which they are distinct. Now equality implies both —namely, distinction of persons, for nothing can be said to be equal to itself; and unity of essence, since for this reason are the persons equal to one another, that they are of the same greatness and essence. Now it is clear that the relation of a thing to itself is not a real relation. Nor, again, is one relation referred to another by a further relation: for when we say that paternity is opposed to filiation, opposition is not a relation mediating between paternity and filiation. For in both these cases relation would be multiplied indefinitely. Therefore equality and likeness in the divine persons is not a real relation distinct from the personal relations: but in its concept it includes both the relations which distinguish the persons, and the unity of essence. For this reason the Master says (Sent. i, D, xxxi) that in these "it is only the terms that are relative."

Article 2. Whether the person proceeding is co-eternal with His principle, as the Son with the Father?

Objection 1. It would seem that the person proceeding is not co-eternal with His principle, as the Son with the Father. For Arius gives twelve modes of generation. The first mode is like the issue of a line from a point; wherein is wanting equality of simplicity. The second is like the emission of rays from the sun; wherein is absent equality of nature. The third is like the mark or impression made by a seal; wherein is wanting consubstantiality and executive power. The fourth is the infusion of a good will from God; wherein also consubstantiality is wanting. The fifth is the emanation of an accident from its subject; but the accident has no subsistence. The sixth is the abstraction of a species from matter, as sense receives the species from the sensible object; wherein is wanting equality of spiritual simplicity. The seventh is the exciting of the will by knowledge, which excitation is merely temporal. The eighth is transformation, as an image is made of brass; which transformation is material. The ninth is motion from a mover; and here again we have effect and cause. The tenth is the taking of species from genera; but this mode has no place in God, for the Father is not predicated of the Son as the genus of a species. The eleventh is the realization of an idea [ideatio], as an external coffer arises from the one in the mind. The twelfth is birth, as a man is begotten of his father; which implies priority and posteriority of time. Thus it is clear that equality of nature or of time is absent in every mode whereby one thing is from another. So if the Son is from the Father, we must say that He is less than the Father, or later than the Father, or both.

Objection 2. Further, everything that comes from another has a principle. But nothing eternal has a principle. Therefore the Son is not eternal; nor is the Holy Ghost.

Objection 3. Further, everything which is corrupted ceases to be. Hence everything generated begins to be; for the end of generation is existence. But the Son is generated by the Father. Therefore He begins to exist, and is not co-eternal with the Father.

Objection 4. Further, if the Son be begotten by the Father, either He is always being begotten, or there is some moment in which He is begotten. If He is always being begotten, since, during the process of generation, a thing must be imperfect, as appears in successive things, which are always in process of becoming, as time and motion, it follows that the Son must be always imperfect, which cannot be admitted. Thus there is a moment to be assigned for the begetting of the Son, and before that moment the Son did not exist.

On the contrary, Athanasius declares that "all the three persons are co-eternal with each other."

I answer that, We must say that the Son is co-eternal with the Father. In proof of which we must consider that for a thing which proceeds from a principle to be posterior to its principle may be due to two reasons: one on the part of the agent, and the other on the part of the action. On the part of the agent this happens differently as regards free agents and natural agents. In free agents, on account of the choice of time; for as a free agent can choose the form it gives to the effect, as stated above (I:41:2), so it can choose the time in which to produce its effect. In natural agents, however, the same happens from the agent not having its perfection of natural power from the very first, but obtaining it after a certain time; as, for instance, a man is not able to generate from the very first. Considered on the part of action, anything derived from a principle cannot exist simultaneously with its principle when the action is successive. So, given that an agent, as soon as it exists, begins to act thus, the effect would not exist in the same instant, but in the instant of the action's termination. Now it is manifest, according to what has been said (I:41:2, that the Father does not beget the Son by will, but by nature; and also that the Father's nature was perfect from eternity; and again that the action whereby the Father produces the Son is not successive, because thus the Son would be successively generated, and this generation would be material, and accompanied with movement; which is quite impossible. Therefore we conclude that the Son existed whensoever the Father existed and thus the Son is co-eternal with the Father, and likewise the Holy Ghost is co-eternal with both.

Reply to Objection 1. As Augustine says (De Verbis Domini, Serm. 38), no mode of the procession of any creature perfectly represents the divine generation. Hence we need to gather a likeness of it from many of these modes, so that what is wanting in one may be somewhat supplied from another; and thus it is declared in the council of Ephesus: "Let Splendor tell thee that the co-eternal Son existed always with the Father; let the Word announce the impassibility of His birth; let the name Son insinuate His consubstantiality." Yet, above them all the procession of the word from the intellect represents it more exactly; the intellectual word not being posterior to its source except in an intellect passing from potentiality to act; and this cannot be said of God.

Reply to Objection 2. Eternity excludes the principle of duration, but not the principle of origin.

Reply to Objection 3. Every corruption is a change; and so all that corrupts begins not to exist and ceases to be. The divine generation, however, is not changed, as stated above (I:27:2). Hence the Son is ever being begotten, and the Father is always begetting.

Reply to Objection 4. In time there is something indivisible—namely, the instant; and there is something else which endures—namely, time. But in eternity the indivisible "now" stands ever still, as we have said above (I:10:2 ad 1, I:10:4 ad 2). But the generation of the Son is not in the "now" of time, or in time, but in eternity. And so to express the presentiality and permanence of eternity, we can say that "He is ever being born," as Origen said (Hom. in Joan. i). But as Gregory [Moral. xxix, 21] and Augustine [Super Ps. 2:7] said, it is better to say "ever born," so that "ever" may denote the permanence of eternity, and "born" the perfection of the only Begotten. Thus, therefore, neither is the Son imperfect, nor "was there a time when He was not," as Arius said.

Article 3. Whether in the divine persons there exists an order of nature?

Objection 1. It would seem that among the divine persons there does not exist an order of nature. For whatever exists in God is the essence, or a person, or a notion. But the order of nature does not signify the essence, nor any of the persons, or notions. Therefore there is no order of nature in God.

Objection 2. Further, wherever order of nature exists, there one comes before another, at least, according to nature and intellect. But in the divine persons there exists neither priority nor posteriority, as declared by Athanasius. Therefore, in the divine persons there is no order of nature.

Objection 3. Further, wherever order exists, distinction also exists. But there is no distinction in the divine nature. Therefore it is not subject to order; and order of nature does not exist in it.

Objection 4. Further, the divine nature is the divine essence. But there is no order of essence in God. Therefore neither is there of nature.

On the contrary, Where plurality exists without order, confusion exists. But in the divine persons there is no confusion, as Athanasius says. Therefore in God order exists.

I answer that, Order always has reference to some principle. Wherefore since there are many kinds of principle—namely, according to site, as a point; according to intellect, as the principle of demonstration; and according to each individual cause—so are there many kinds of order. Now principle, according to origin, without priority, exists in God as we have stated (I:33:1: so there must likewise be order according to origin, without priority; and this is called 'the order of nature': in the words of Augustine (Contra Maxim. iv): "Not whereby one is prior to another, but whereby one is from another."

Reply to Objection 1. The order of nature signifies the notion of origin in general, not a special kind of origin.

Reply to Objection 2. In things created, even when what is derived from a principle is co-equal in duration with its principle, the principle still comes first in the order of nature and reason, if formally considered as principle. If, however, we consider the relations of cause and effect, or of the principle and the thing proceeding therefrom, it is clear that the things so related are simultaneous in the order of nature and reason, inasmuch as the one enters the definition of the other. But in God the relations themselves are the persons subsisting in one nature. So, neither on the part of the nature, nor on the part the relations, can one person be prior to another, not even in the order of nature and reason.

Reply to Objection 3. The order of nature means not the ordering of nature itself, but the existence of order in the divine Persons according to natural origin.

Reply to Objection 4. Nature in a certain way implies the idea of a principle, but essence does not; and so the order of origin is more correctly called the order of nature than the order of essence.

Article 4. Whether the Son is equal to the Father in greatness?

Objection 1. It would seem that the Son is not equal to the Father in greatness. For He Himself said (John 14:28): "The Father is greater than I"; and the Apostle says (1 Corinthians 15:28): "The Son Himself shall be subject to Him that put all things under Him."

Objection 2. Further, paternity is part of the Father's dignity. But paternity does not belong to the Son. Therefore the Son does not possess all the Father's dignity; and so He is not equal in greatness to the Father.

Objection 3. Further, wherever there exist a whole and a part, many parts are more than one only, or than fewer parts; as three men are more than two, or than one. But in God a universal whole exists, and a part; for under relation or notion, several notions are included. Therefore, since in the Father there are three notions, while in the Son there are only two, the Son is evidently not equal to the Father.

On the contrary, It is said (Philippians 2:6): "He thought it not robbery to be equal with God."

I answer that, The Son is necessarily equal to the Father in greatness. For the greatness of God is nothing but the perfection of His nature. Now it belongs to the very nature of paternity and filiation that the Son by generation should attain to the possession of the perfection of the nature which is in the Father, in the same way as it is in the Father Himself. But since in men generation is a certain kind of transmutation of one proceeding from potentiality to act, it follows that a man is not equal at first to the father who begets him, but attains to equality by due growth, unless owing to a defect in the principle of generation it should happen otherwise. From what precedes (I:27:2; I:33:3), it is evident that in God there exist real true paternity and filiation. Nor can we say that the power of generation in the Father was defective, nor that the Son of God arrived at perfection in a successive manner and by change. Therefore we must say that the Son was eternally equal to the Father in greatness. Hence, Hilary says (De Synod. Can. 27): "Remove bodily weakness, remove the beginning of conception, remove pain and all human shortcomings, then every son, by reason of his natural nativity, is the father's equal, because he has a like nature."

Reply to Objection 1. These words are to be understood of Christ's human nature, wherein He is less than the Father, and subject to Him; but in His divine nature He is equal to the Father. This is expressed by Athanasius, "Equal to the Father in His Godhead; less than the Father in humanity": and by Hilary (De Trin. ix): "By the fact of giving, the Father is greater; but He is not less to Whom the same being is given"; and (De Synod.): "The Son subjects Himself by His inborn piety"—that is, by His recognition of paternal authority; whereas "creatures are subject by their created weakness."

Reply to Objection 2. Equality is measured by greatness. In God greatness signifies the perfection of nature, as above explained (Article 1, Reply to Objection 1), and belongs to the essence. Thus equality and likeness in God have reference to the essence; nor can there be inequality or dissimilitude arising from the distinction of the relations. Wherefore Augustine says (Contra Maxim. iii, 13), "The question of origin is, Who is from whom? but the question of equality is, Of what kind, or how great, is he?" Therefore, paternity is the Father's dignity, as also the Father's essence: since dignity is something absolute, and pertains to the essence. As, therefore, the same essence, which in the Father is paternity, in the Son is filiation, so the same dignity which, in the Father is paternity, in the Son is filiation. It is thus true to say that the Son possesses whatever dignity the Father has; but we cannot argue—"the Father has paternity, therefore the Son has paternity," for there is a transition from substance to relation. For the Father and the Son have the same essence and dignity, which exist in the Father by the relation of giver, and in the Son by relation of receiver.

Reply to Objection 3. In God relation is not a universal whole, although it is predicated of each of the relations; because all the relations are one in essence and being, which is irreconcilable with the idea of universal, the parts of which are distinguished in being. Persons likewise is not a universal term in God as we have seen above (I:30:4). Wherefore all the relations together are not greater than only one; nor are all the persons something greater than only one; because the whole perfection of the divine nature exists in each person.

Article 5. Whether the Son is in the Father, and conversely?

Objection 1. It would seem that the Son and the Father are not in each other. For the Philosopher (Phys. iv, text. 23) gives eight modes of one thing existing in another, according to none of which is the Son in the Father, or conversely; as is patent to anyone who examines each mode. Therefore the Son and the Father are not in each other.

Objection 2. Further, nothing that has come out from another is within it. But the Son from eternity came out from the Father, according to Micheas v. 2: "His going forth is from the beginning, from the days of eternity." Therefore the Son is not in the Father.

Objection 3. Further, one of two opposites cannot be in the other. But the Son and the Father are relatively opposed. Therefore one cannot be in the other.

On the contrary, It is said (John 14:10): "I am in the Father, and the Father is in Me."

I answer that, There are three points of consideration as regards the Father and the Son; the essence, the relation, and the origin; and according to each the Son and the Father are in each other. The Father is in the Son by His essence, forasmuch as the Father is His own essence, and communicates His essence to the Son not by any change on His part. Hence it follows that as the Father's essence is in the Son, the Father Himself is in the Son; likewise, since the Son is His own essence, it follows that He Himself is in the Father in Whom is His essence. This is expressed by Hilary (De Trin. v), "The unchangeable God, so to speak, follows His own nature in begetting an unchangeable subsisting God. So we understand the nature of God to subsist in Him, for He is God in God." It is also manifest that as regards the relations, each of two relative opposites is in the concept of the other. Regarding origin also, it is clear that the procession of the intelligible word is not outside the intellect, inasmuch as it remains in the utterer of the word. What also is uttered by the word is therein contained. And the same applies to the Holy Ghost.

Reply to Objection 1. What is contained in creatures does not sufficiently represent what exists in God; so according to none of the modes enumerated by the Philosopher, are the Son and the Father in each other. The mode the most nearly approaching to the reality is to be found in that whereby something exists in its originating principle, except that the unity of essence between the principle and that which proceeds therefrom is wanting in things created.

Reply to Objection 2. The Son's going forth from the Father is by mode of the interior procession whereby the word emerges from the heart and remains therein. Hence this going forth in God is only by the distinction of the relations, not by any kind of essential separation.

Reply to Objection 3. The Father and the Son are relatively opposed, but not essentially; while, as above explained, one relative opposite is in the other.

Article 6. Whether the Son is equal to the Father in power?

Objection 1. It would seem that the Son is not equal to the Father in power. For it is said (John 5:19): "The Son cannot do anything of Himself but what He seeth the Father doing." But the Father can act of Himself. Therefore the Father's power is greater than the Son's.

Objection 2. Further, greater is the power of him who commands and teaches than of him who obeys and hears. But the Father commands the Son according to John 14:31: "As the Father gave Me commandment so do I." The Father also teaches the Son: "The Father loveth the Son, and showeth Him all things that Himself doth" (John 5:20). Also, the Son hears: "As I hear, so I judge" (John 5:30). Therefore the Father has greater power than the Son.

Objection 3. Further, it belongs to the Father's omnipotence to be able to beget a Son equal to Himself. For Augustine says (Contra Maxim. iii, 7), "Were He unable to beget one equal to Himself, where would be the omnipotence of God the Father?" But the Son cannot beget a Son, as proved above (I:41:6). Therefore the Son cannot do all that belongs to the Father's omnipotence; and hence He is not equal to Him power.

On the contrary, It is said (John 5:19): "Whatsoever things the Father doth, these the Son also doth in like manner."

I answer that, The Son is necessarily equal to the Father in power. Power of action is a consequence of perfection in nature. In creatures, for instance, we see that the more perfect the nature, the greater power is there for action. Now it was shown above (Article 4) that the very notion of the divine paternity and filiation requires that the Son should be the Father's equal in greatness—that is, in perfection of nature. Hence it follows that the Son is equal to the Father in power; and the same applies to the Holy Ghost in relation to both.

Reply to Objection 1. The words, "the Son cannot of Himself do anything," do not withdraw from the Son any power possessed by the Father, since it is immediately added, "Whatsoever things the Father doth, the Son doth in like manner"; but their meaning is to show that the Son derives His power from the Father, of Whom He receives His nature. Hence, Hilary says (De Trin. ix), "The unity of the divine nature implies that the Son so acts of Himself [per se], that He does not act by Himself [a se]."

Reply to Objection 2. The Father's "showing" and the Son's "hearing" are to be taken in the sense that the Father communicates knowledge to the Son, as He communicates His essence. The command of the Father can be explained in the same sense, as giving Him from eternity knowledge and will to act, by begetting Him. Or, better still, this may be referred to Christ in His human nature.

Reply to Objection 3. As the same essence is paternity in the Father, and filiation in the Son: so by the same power the Father begets, and the Son is begotten. Hence it is clear that the Son can do whatever the Father can do; yet it does not follow that the Son can beget; for to argue thus would imply transition from substance to relation, for generation signifies a divine relation. So the Son has the same omnipotence as the Father, but with another relation; the Father possessing power as "giving" signified when we say that He is able to beget; while the Son possesses the power of "receiving," signified by saying that He can be begotten.

The Summa Theologiæ of St. Thomas Aquinas
Second and Revised Edition, 1920
Literally translated by Fathers of the English Dominican Province
Online Edition Copyright © 2017 by Kevin Knight
Nihil Obstat. F. Innocentius Apap, O.P., S.T.M., Censor. Theol.
Imprimatur. Edus. Canonicus Surmont, Vicarius Generalis. Westmonasterii.
Nihil Obstat. F. Raphael Moss, O.P., S.T.L. and F. Leo Moore, O.P., S.T.L.
Imprimatur. F. Beda Jarrett, O.P., S.T.L., A.M., Prior Provincialis Angliæ


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