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Home > Summa Theologiae > First Part > Question 31

Question 31. The unity or plurality in God

  1. The word "Trinity"
  2. Can we say that the Son is other than the Father?
  3. Can an exclusive term, which seems to exclude otherness, be joined to an essential name in God?
  4. Can it be joined to a personal term?

Article 1. Whether there is trinity in God?

Objection 1. It would seem there is not trinity in God. For every name in God signifies substance or relation. But this name "Trinity" does not signify the substance; otherwise it would be predicated of each one of the persons: nor does it signify relation; for it does not express a name that refers to another. Therefore the word "Trinity" is not to be applied to God.

Objection 2. Further, this word "trinity" is a collective term, since it signifies multitude. But such a word does not apply to God; as the unity of a collective name is the least of unities, whereas in God there exists the greatest possible unity. Therefore this word "trinity" does not apply to God.

Objection 3. Further, every trine is threefold. But in God there is not triplicity; since triplicity is a kind of inequality. Therefore neither is there trinity in God.

Objection 4. Further, all that exists in God exists in the unity of the divine essence; because God is His own essence. Therefore, if Trinity exists in God, it exists in the unity of the divine essence; and thus in God there would be three essential unities; which is heresy.

Objection 5. Further, in all that is said of God, the concrete is predicated of the abstract; for Deity is God and paternity is the Father. But the Trinity cannot be called trine; otherwise there would be nine realities in God; which, of course, is erroneous. Therefore the word trinity is not to be applied to God.

On the contrary, Athanasius says: "Unity in Trinity; and Trinity in Unity is to be revered."

I answer that, The name "Trinity" in God signifies the determinate number of persons. And so the plurality of persons in God requires that we should use the word trinity; because what is indeterminately signified by plurality, is signified by trinity in a determinate manner.

Reply to Objection 1. In its etymological sense, this word "Trinity" seems to signify the one essence of the three persons, according as trinity may mean trine-unity. But in the strict meaning of the term it rather signifies the number of persons of one essence; and on this account we cannot say that the Father is the Trinity, as He is not three persons. Yet it does not mean the relations themselves of the Persons, but rather the number of persons related to each other; and hence it is that the word in itself does not express regard to another.

Reply to Objection 2. Two things are implied in a collective term, plurality of the "supposita," and a unity of some kind of order. For "people" is a multitude of men comprehended under a certain order. In the first sense, this word "trinity" is like other collective words; but in the second sense it differs from them, because in the divine Trinity not only is there unity of order, but also with this there is unity of essence.

Reply to Objection 3. "Trinity" is taken in an absolute sense; for it signifies the threefold number of persons. "Triplicity" signifies a proportion of inequality; for it is a species of unequal proportion, according to Boethius (Arithm. i, 23). Therefore in God there is not triplicity, but Trinity.

Reply to Objection 4. In the divine Trinity is to be understood both number and the persons numbered. So when we say, "Trinity in Unity," we do not place number in the unity of the essence, as if we meant three times one; but we place the Persons numbered in the unity of nature; as the "supposita" of a nature are said to exist in that nature. On the other hand, we say "Unity in Trinity"; meaning that the nature is in its "supposita."

Reply to Objection 5. When we say, "Trinity is trine," by reason of the number implied, we signify the multiplication of that number by itself; since the word trine imports a distinction in the "supposita" of which it is spoken. Therefore it cannot be said that the Trinity is trine; otherwise it follows that, if the Trinity be trine, there would be three "supposita" of the Trinity; as when we say, "God is trine," it follows that there are three "supposita" of the Godhead.

Article 2. Whether the Son is other than the Father?

Objection 1. It would seem that the Son is not other than the Father. For "other" is a relative term implying diversity of substance. If, then, the Son is other than the Father, He must be different from the Father; which is contrary to what Augustine says (De Trin. vii), that when we speak of three persons, "we do not mean to imply diversity."

Objection 2. Further, whosoever are other from one another, differ in some way from one another. Therefore, if the Son is other than the Father, it follows that He differs from the Father; which is against what Ambrose says (De Fide i), that "the Father and the Son are one in Godhead; nor is there any difference in substance between them, nor any diversity."

Objection 3. Further, the term alien is taken from "alius" [other]. But the Son is not alien from the Father, for Hilary says (De Trin. vii) that "in the divine persons there is nothing diverse, nothing alien, nothing separable." Therefore the Son is not other than the Father.

Objection 4. Further, the terms "other person" and "other thing" [alius et aliud] have the same meaning, differing only in gender. So if the Son is another person from the Father, it follows that the Son is a thing apart from the Father.

On the contrary, Augustine [Fulgentius, De Fide ad Petrum i.] says: "There is one essence of the Father and Son and Holy Ghost, in which the Father is not one thing, the Son another, and the Holy Ghost another; although the Father is one person, the Son another, and the Holy Ghost another."

I answer that, Since as Jerome remarks [In substance, Ep. lvii.], a heresy arises from words wrongly used, when we speak of the Trinity we must proceed with care and with befitting modesty; because, as Augustine says (De Trin. i, 3), "nowhere is error more harmful, the quest more toilsome, the finding more fruitful." Now, in treating of the Trinity, we must beware of two opposite errors, and proceed cautiously between them—namely, the error of Arius, who placed a Trinity of substance with the Trinity of persons; and the error of Sabellius, who placed unity of person with the unity of essence.

Thus, to avoid the error of Arius we must shun the use of the terms diversity and difference in God, lest we take away the unity of essence: we may, however, use the term "distinction" on account of the relative opposition. Hence whenever we find terms of "diversity" or "difference" of Persons used in an authentic work, these terms of "diversity" or "difference" are taken to mean "distinction." But lest the simplicity and singleness of the divine essence be taken away, the terms "separation" and "division," which belong to the parts of a whole, are to be avoided: and lest quality be taken away, we avoid the use of the term "disparity": and lest we remove similitude, we avoid the terms "alien" and "discrepant." For Ambrose says (De Fide i) that "in the Father and the Son there is no discrepancy, but one Godhead": and according to Hilary, as quoted above, "in God there is nothing alien, nothing separable."

To avoid the heresy of Sabellius, we must shun the term "singularity," lest we take away the communicability of the divine essence. Hence Hilary says (De Trin. vii): "It is sacrilege to assert that the Father and the Son are separate in Godhead." We must avoid the adjective "only" [unici] lest we take away the number of persons. Hence Hilary says in the same book: "We exclude from God the idea of singularity or uniqueness." Nevertheless, we say "the only Son," for in God there is no plurality of Sons. Yet, we do not say "the only God," for the Deity is common to several. We avoid the word "confused," lest we take away from the Persons the order of their nature. Hence Ambrose says (De Fide i): "What is one is not confused; and there is no multiplicity where there is no difference." The word "solitary" is also to be avoided, lest we take away the society of the three persons; for, as Hilary says (De Trin. iv), "We confess neither a solitary nor a diverse God."

This word "other" [alius], however, in the masculine sense, means only a distinction of "suppositum"; and hence we can properly say that "the Son is other than the Father," because He is another "suppositum" of the divine nature, as He is another person and another hypostasis.

Reply to Objection 1. "Other," being like the name of a particular thing, refers to the "suppositum"; and so, there is sufficient reason for using it, where there is a distinct substance in the sense of hypostasis or person. But diversity requires a distinct substance in the sense of essence. Thus we cannot say that the Son is diverse from the Father, although He is another.

Reply to Objection 2. "Difference" implies distinction of form. There is one form in God, as appears from the text, "Who, when He was in the form of God" (Philippians 2:6). Therefore the term "difference" does not properly apply to God, as appears from the authority quoted. Yet, Damascene (De Fide Orth. i, 5) employs the term "difference" in the divine persons, as meaning that the relative property is signified by way of form. Hence he says that the hypostases do not differ from each other in substance, but according to determinate properties. But "difference" is taken for "distinction," as above stated.

Reply to Objection 3. The term "alien" means what is extraneous and dissimilar; which is not expressed by the term "other" [alius]; and therefore we say that the Son is "other" than the Father, but not that He is anything "alien."

Reply to Objection 4. The neuter gender is formless; whereas the masculine is formed and distinct; and so is the feminine. So the common essence is properly and aptly expressed by the neuter gender, but by the masculine and feminine is expressed the determined subject in the common nature. Hence also in human affairs, if we ask, Who is this man? we answer, Socrates, which is the name of the "suppositum"; whereas, if we ask, What is he? we reply, A rational and mortal animal. So, because in God distinction is by the persons, and not by the essence, we say that the Father is other than the Son, but not something else; while conversely we say that they are one thing, but not one person.

Article 3. Whether the exclusive word "alone" should be added to the essential term in God?

Objection 1. It would seem that the exclusive word "alone" [solus] is not to be added to an essential term in God. For, according to the Philosopher (Elench. ii, 3), "He is alone who is not with another." But God is with the angels and the souls of the saints. Therefore we cannot say that God is alone.

Objection 2. Further, whatever is joined to the essential term in God can be predicated of every person "per se," and of all the persons together; for, as we can properly say that God is wise, we can say the Father is a wise God; and the Trinity is a wise God. But Augustine says (De Trin. vi, 9): "We must consider the opinion that the Father is not true God alone." Therefore God cannot be said to be alone.

Objection 3. Further if this expression "alone" is joined to an essential term, it would be so joined as regards either the personal predicate or the essential predicate. But it cannot be the former, as it is false to say, "God alone is Father," since man also is a father; nor, again, can it be applied as regards the latter, for, if this saying were true, "God alone creates," it would follow that the "Father alone creates," as whatever is said of God can be said of the Father; and it would be false, as the Son also creates. Therefore this expression "alone" cannot be joined to an essential term in God.

On the contrary, It is said, "To the King of ages, immortal, invisible, the only God" (1 Timothy 1:17).

I answer that, This term "alone" can be taken as a categorematical term, or as a syncategorematical term. A categorematical term is one which ascribes absolutely its meaning to a given "suppositum"; as, for instance, "white" to man, as when we say a "white man." If the term "alone" is taken in this sense, it cannot in any way be joined to any term in God; for it would mean solitude in the term to which it is joined; and it would follow that God was solitary, against what is above stated (Article 2). A syncategorematical term imports the order of the predicate to the subject; as this expression "every one" or "no one"; and likewise the term "alone," as excluding every other "suppositum" from the predicate. Thus, when we say, "Socrates alone writes," we do not mean that Socrates is solitary, but that he has no companion in writing, though many others may be with him. In this way nothing prevents the term "alone" being joined to any essential term in God, as excluding the predicate from all things but God; as if we said "God alone is eternal," because nothing but God is eternal.

Reply to Objection 1. Although the angels and the souls of the saints are always with God, nevertheless, if plurality of persons did not exist in God, He would be alone or solitary. For solitude is not removed by association with anything that is extraneous in nature; thus anyone is said to be alone in a garden, though many plants and animals are with him in the garden. Likewise, God would be alone or solitary, though angels and men were with Him, supposing that several persons were not within Him. Therefore the society of angels and of souls does not take away absolute solitude from God; much less does it remove respective solitude, in reference to a predicate.

Reply to Objection 2. This expression "alone," properly speaking, does not affect the predicate, which is taken formally, for it refers to the "suppositum," as excluding any other suppositum from the one which it qualifies. But the adverb "only," being exclusive, can be applied either to subject or predicate. For we can say, "Only Socrates"—that is, no one else—"runs: and Socrates runs only"—that is, he does nothing else. Hence it is not properly said that the Father is God alone, or the Trinity is God alone, unless some implied meaning be assumed in the predicate, as, for instance, "The Trinity is God Who alone is God." In that sense it can be true to say that the Father is that God Who alone is God, if the relative be referred to the predicate, and not to the "suppositum." So, when Augustine says that the Father is not God alone, but that the Trinity is God alone, he speaks expositively, as he might explain the words, "To the King of ages, invisible, the only God," as applying not to the Father, but to the Trinity alone.

Reply to Objection 3. In both ways can the term "alone" be joined to an essential term. For this proposition, "God alone is Father," can mean two things, because the word "Father" can signify the person of the Father; and then it is true; for no man is that person: or it can signify that relation only; and thus it is false, because the relation of paternity is found also in others, though not in a univocal sense. Likewise it is true to say God alone creates; nor, does it follow, "therefore the Father alone creates," because, as logicians say, an exclusive diction so fixes the term to which it is joined that what is said exclusively of that term cannot be said exclusively of an individual contained in that term: for instance, from the premiss, "Man alone is a mortal rational animal," we cannot conclude, "therefore Socrates alone is such."

Article 4. Whether an exclusive diction can be joined to the personal term?

Objection 1. It would seem that an exclusive diction can be joined to the personal term, even though the predicate is common. For our Lord speaking to the Father, said: "That they may know Thee, the only true God" (John 17:3). Therefore the Father alone is true God.

Objection 2. Further, He said: "No one knows the Son but the Father" (Matthew 11:27); which means that the Father alone knows the Son. But to know the Son is common (to the persons). Therefore the same conclusion follows.

Objection 3. Further, an exclusive diction does not exclude what enters into the concept of the term to which it is joined. Hence it does not exclude the part, nor the universal; for it does not follow that if we say "Socrates alone is white," that therefore "his hand is not white," or that "man is not white." But one person is in the concept of another; as the Father is in the concept of the Son; and conversely. Therefore, when we say, The Father alone is God, we do not exclude the Son, nor the Holy Ghost; so that such a mode of speaking is true.

Objection 4. Further, the Church sings: "Thou alone art Most High, O Jesus Christ."

On the contrary, This proposition "The Father alone is God" includes two assertions—namely, that the Father is God, and that no other besides the Father is God. But this second proposition is false, for the Son is another from the Father, and He is God. Therefore this is false, The Father alone is God; and the same of the like sayings.

I answer that, When we say, "The Father alone is God," such a proposition can be taken in several senses. If "alone" means solitude in the Father, it is false in a categorematical sense; but if taken in a syncategorematical sense it can again be understood in several ways. For if it exclude (all others) from the form of the subject, it is true, the sense being "the Father alone is God"—that is, "He who with no other is the Father, is God." In this way Augustine expounds when he says (De Trin. vi, 6): "We say the Father alone, not because He is separate from the Son, or from the Holy Ghost, but because they are not the Father together with Him." This, however, is not the usual way of speaking, unless we understand another implication, as though we said "He who alone is called the Father is God." But in the strict sense the exclusion affects the predicate. And thus the proposition is false if it excludes another in the masculine sense; but true if it excludes it in the neuter sense; because the Son is another person than the Father, but not another thing; and the same applies to the Holy Ghost. But because this diction "alone," properly speaking, refers to the subject, it tends to exclude another Person rather than other things. Hence such a way of speaking is not to be taken too literally, but it should be piously expounded, whenever we find it in an authentic work.

Reply to Objection 1. When we say, "Thee the only true God," we do not understand it as referring to the person of the Father, but to the whole Trinity, as Augustine expounds (De Trin. vi, 9). Or, if understood of the person of the Father, the other persons are not excluded by reason of the unity of essence; in so far as the word "only" excludes another thing, as above explained.

The same Reply can be given to Objection 2. For an essential term applied to the Father does not exclude the Son or the Holy Ghost, by reason of the unity of essence. Hence we must understand that in the text quoted the term "no one" [Nemo = non-homo, i.e. no man] is not the same as "no man," which the word itself would seem to signify (for the person of the Father could not be excepted), but is taken according to the usual way of speaking in a distributive sense, to mean any rational nature.

Reply to Objection 3. The exclusive diction does not exclude what enters into the concept of the term to which it is adjoined, if they do not differ in "suppositum," as part and universal. But the Son differs in "suppositum" from the Father; and so there is no parity.

Reply to Objection 4. We do not say absolutely that the Son alone is Most High; but that He alone is Most High "with the Holy Ghost, in the glory of God the Father."

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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