Summa summae S. Thomae sive compendium theologiae

There were three principal heresies against this mystery. The first was that of Sabellius, who denied the distinction of Persons. The second was that of Arius, who denied their consubstantiality. The third was that of Macedonius, who attacked the divinity of the Holy Spirit. All heresies in this matter can be referred back to these three headings.

These three heresies, long since suppressed, were revived by the Socinians around the middle of the sixteenth century, who asserted that the Father, the Son, and the Holy Spirit are indeed three, yet not three Persons, nor of the same substance, and that the Father alone is the true God.¹

I say: There is one God, numerically and individually, in three Persons — that is, one and the same individual divine essence in three really distinct Persons: the Father unbegotten, the Son begotten, the Holy Spirit proceeding.

Proof from the Old Testament. 1° Genesis I, 26: God said: Let us make man in our image and likeness. — Behold plurality. And immediately after, v. 27: He created man in his own image. — Behold unity. 2° Genesis XVIII, 1–3: The Lord appeared to him [Abraham] in the valley of Mambre… And when he raised his eyes, there appeared to him three men standing near him; and when he saw them… he bowed to the ground. And said: Lord, if I have found favour in your eyes. Weighing these words, Augustine, Against Maximinus, bk. II, c. 26, n. 5, says: "He sees three, yet calls them not 'lords' but 'Lord,' because the Trinity indeed consists of three Persons, but there is one Lord God."

Proof from the New Testament. 1° Matthew XXVIII, 19: Baptizing them in the name of the Father, and of the Son, and of the Holy Spirit. In these words the unity of essence is indicated by the singular in the name — not in the names — and the Trinity of Persons by the enumeration: of the Father, and of the Son, and of the Holy Spirit. 2° 1 John V, 7: There are three who give testimony in heaven: the Father, the Word, and the Holy Spirit; and these three are one.

Against this most forceful testimony the Socinians attack two things: the authenticity of the text and its meaning. Regarding the authenticity of the text, they say that this seventh verse of chapter V of the First Epistle of John is spurious: (1) because it is not found in the more ancient and well-attested manuscripts; (2) because it was not cited by Athanasius, Hilary, Chrysostom, Ambrose, Gregory Nazianzen, and others against the Arians and Sabellians, even though it would have been most apt for refuting them. To the first objection, we admit that this verse, whether in full or in part, is not found in certain ancient manuscript copies; but it is found in far more of the most ancient and best-attested manuscripts.

That it is absent from a few copies could have occurred: (1) through the treachery of the Arians, who erased this text as too contrary to their error, as Jerome attests in his Prologue to the Catholic Epistles — if indeed that Prologue is Jerome's, a point currently debated by critics. But whatever the case, St. Ambrose frequently reproaches the Arians for this sort of fraud: On the Faith, bk. II, c. 15; bk. III, c. 16; On the Holy Spirit, bk. IV, c. 40. (2) The omission could also have arisen from a copyist's error: having arrived at the words of verse 7, There are three who give testimony, his eye skipped to verse 8, where the same words are repeated. This slip is common among copyists when the same words are repeated with scarcely any interval.

Moreover, our Vulgate edition was made according to the copies which were in everyday use among the faithful. These are far more difficult to corrupt, owing to their daily use and the certain risk of the fraud being detected; they therefore deserve far greater credibility than those that lie hidden in the corners of libraries, where through the negligence or malice of copyists they lie open to tampering and falsification.

To the second objection — that several Fathers did not cite this verse against heretics — I reply that several others did cite it. Tertullian cited it, Against Praxeas, c. 31; St. Cyprian, On the Unity of the Church; Jerome, in his Prologue to the Catholic Epistles; Cassiodorus, Fulgentius, and several others. This positive proof certainly outweighs the negative argument of the Socinians. Hence, that we do not read this verse having been cited in the writings of certain ancients is probably due to the fact that they happened upon a defective codex, or that not all their writings have come down to us, or that they were corrupted by enemies of the faith.¹

Regarding the meaning of this verse, the Socinians say that the words and these three are one do not signify unity of nature or substance, but unity of testimony — because in verse 8 following, of the spirit, the blood, and the water it is likewise said: and these three are one, which is not understood as unity of nature but of testimony, insofar as they concur in the same testimony about Christ, namely that he is the truth, just as the Father, the Son, and the Holy Spirit do. Reply 1°: These words of verse 8, and these three are one, are absent from many Latin codices. The Louvain correctors count fifteen in which they are not read. Innocent III, in the decretal found in Decretals III, tit. 41, c. In quadam, says that "in most codices" — probably Latin ones — "they are not found." The Greek codices do have them, yet not as cited, but thus: and these three are unto one [in unum], that is, they concur in one testimony. It is therefore rightly presumed that, through Arian fraud or copyist negligence, the word in dropped out of the Latin codices that contain these words. But even if our Vulgate does not read it that way, it must still be so explained as to correspond to the Greek original, so that the sense is: the spirit, the water, and the blood concur in attesting the same thing, namely that Christ is true man. And although in both verses there is a certain parallel in rendering testimony, it is not necessary that there be a parallel in the signification of the words and these three are one.

Reply 2°: Granted that these words express a parallel, that parallel is indeed found; for these three — Spirit, Water, and Blood — are in some manner substantially one. Let the sense then be: The Spirit, Water, and Blood gave testimony about Christ at the time of his passion: the Spirit, when he cried out and expired; the Blood and Water flowing from his side. And these three are substantially one, that is, they belong to one and the same human substance in Christ — just as the Father, the Son, and the Holy Spirit belong to one and the same divine substance — with this difference, however, that the divine substance is supremely simple and one, while the human substance is composite. 3° John X, 30: I and the Father are one. I and the Father are — behold the distinction of Persons; one — behold consubstantiality. Hence Augustine, Tract. XXXVI on John ch. VIII, says: "What he said, one, frees you from Arius; what he said, are, frees you from Sabellius." This passage was urged most forcefully by the Fathers against the heretics.

4° What could be plainer than John I, 1: In the beginning was the Word, and the Word was with God, and the Word was God?

Proof of the conclusion from Tradition. 1° From the form of Baptism which has been constantly in use from the very beginning of the Church; this form contains a profession of three Persons in one numerically identical substance, as we have considered above.

2° From the protest of the whole Church against the heresies that arose concerning this mystery — those of Sabellius, Arius, Macedonius, and others. From this it is clear that this is and has been the ancient and constant teaching of the faithful.

3° From the holy Fathers who in the first three centuries before the Council of Nicaea expressed this faith in their writings.

First century. Hermas, disciple of Paul, in the work called The Shepherd, bk. III, Similitudes 5 and 9. St. Clement, fellow worker of Paul and successor of Peter in the Roman See, Epistle to the Corinthians, n. 16 and n. 161 [sic — verify]. St. Dionysius the Areopagite, another disciple of St. Paul, On the Divine Names, c. 1. St. Ignatius Martyr, hearer of John the Evangelist, Epistles to the Ephesians and to the Magnesians.

Second century. St. Polycarp, disciple of both St. John the Evangelist and St. Ignatius, bishop of Smyrna, and with him the entire Church of Smyrna, in the letter written about St. Polycarp's martyrdom to the Churches of Pontus, in Eusebius, Ecclesiastical History, bk. IV, c. 15. St. Justin Martyr, Apology II. Athenagoras, the Christian philosopher, Apology for Christians to the Emperors. St. Irenaeus, disciple of St. Polycarp, bishop of Lyons and martyr, Against Heresies, bk. I, c. 2.

Third century. Clement of Alexandria, Paedagogus, bk. I, c. 6. Tertullian, Against Praxeas, c. 2, and On Modesty, c. 21. St. Cyprian, On the Unity of the Church, c. 4.

Finally, in the fourth century: at the Council of Nicaea in the year 325, against Arius, and at the Council of Constantinople in the year 381, against Macedonius, the Catholic faith concerning the Trinity and the consubstantiality of the Persons in one and undivided God was upheld — a faith which all the faithful have since unanimously professed in the Creed sung by the Church.

Objection 1: You will object first: This mystery is contrary to several principles known by the natural light [of reason], and firstly to this one: "Things which are the same as a third thing are the same as each other," upon which the whole art of syllogism rests. For the Persons are identified with the divine essence, and yet are really distinguished from one another. 2nd. This principle is not preserved: "Nothing produces its own being." For the producing Person and the produced Person have the same being. 3rd. It overturns this principle: "Person renders a nature incommunicable to another suppositum [subject];" because the nature which is in the Father is communicated to the Son and to the Holy Spirit. Therefore, this mystery is against reason, and thus impossible.

Response — I deny the antecedent.¹

To the first [objection] I answer, that this axiom must be understood of those things which are the same as a third thing in reality and in concept. In this sense it is explained that this one third thing is not virtually multiple, but that the extremes are united to it under the same formality and concept, not under a different one. Hence, although "action" is the same as "motion," and similarly "passion" [being acted upon], it does not follow that action and passion are the same; because in action a relation is implied as that from which motion exists in a movable object, but in passion as that which is from another. Similarly, although paternity is the same in reality as the divine essence, and similarly filiation, nevertheless these two in their proper concepts imply opposite relations, whence they are distinguished from each other.

So that you may understand this more deeply, note carefully that it is proper to an infinite thing to identify things with itself, preserving their formal concepts, when they do not imply imperfection. Thus, for example, the formal concept of wisdom, which is to know things through their highest cause, and likewise the formal concepts of justice, mercy, etc., are most perfectly preserved in God, notwithstanding their real identity with His essence. But the proper concept of a relation is to be opposed to its correlative and to be really distinguished from it; and accordingly the divine relations, notwithstanding their real identity with the essence, are opposed to each other relatively, and by reason of this opposition they are really distinguished from each other.

If you weigh these things well, you will easily solve whatever objections arise.

To the second I answer, that the Father does not produce His own being, but only communicates it; which He is able to do because that being is of such eminence and fecundity that, remaining the same, it can be possessed by multiple [Persons]: and since it is entirely the same in the Father and in the Son, it is not from the Father as from a cause with dependence, but as from a principle of origin.

To the third principle derived from the definition of person, I answer, this is understood by many in this way: that personality renders incommunicable not the nature in itself, but the composite itself and the person, or the nature reduplicatively as personated. Which is also verified in this mystery; for the Person of the Father, or the divine nature with the mode of paternity and as personated, is not communicated to another; for there is only one Father in the Godhead. Besides, granted that in created things it is understood otherwise—so that in them personality renders the nature itself incommunicable to another suppositum because a created nature, since it is finite, is fulfilled by a single personality—nevertheless, it must be verified in the Godhead in the first sense. This is both because, on account of its infinity and infinite fecundity, it is not equated or fulfilled by one personality, as a created nature is; and also because personality in the Godhead is not something absolute, as in created things, but something relative, and it is of the nature of a relative thing that it has a correlative.

Objection 2: From the infinity of the divine nature we gather, with St. Thomas, that it is one and unmultipliable. But a Person in the Godhead, as virtually distinct from the essence, is also infinite. Therefore, [there is only] one Person.

Response 1. I distinguish the minor premise. A Person in the Godhead, as virtually distinct from the essence, is infinite by reason of the essence which it includes: I concede; by reason of its relative concept precisely: I deny. For since under that respect it does not add perfection, it does not add infinity either, but abstracts from infinity and finitude.

Response 2. Granted the minor premise, I deny the consequence. The disparity is that, since a Person in the Godhead is constituted by a relation, as we shall see below, and this necessarily demands a term to which it refers, it does not imply infinity simply [in an absolute sense], but in a certain genus (e.g., paternity in the concept of paternity): and therefore it does not exclude just any other Person, but only another Father. But indeed, if there were multiple infinite essences, since they would not be opposed to each other relatively, nor consequently distinguished by reason of that opposition, they would have to be distinguished by some formal and essential concept which one would have and not the other, which therefore would not be infinite.

Objection 3: A reason cannot be assigned why there should be three Persons rather than two, or four, or more. Therefore.

Response. I deny the antecedent, and I assign a reason. In God there must be one unproduced Person and two produced, and no more. Therefore.—I prove the antecedent. Personal distinction in the Godhead, as we shall say below, is only according to the relation of origin; from which it follows 1st that there can be only one unproduced Person, since between unproduced Persons there is no given relation of origin. It follows 2nd that, since there are only two processions in the Godhead—one through the intellect, the other through the will (for procession in the Godhead is not considered according to a transient action, but an immanent one, which is twofold: to understand and to will)—there are also consequently only two proceeding Persons, or Persons terminating the twofold procession.—More on this below.

[I say 1°: The mystery of the Most Holy Trinity cannot be known or demonstrated by any natural reason.¹

This is against Abelard and certain others, who maintained that the mysteries of our faith can be demonstrated by reason, whom St. Bernard refuted, lib. V de Consideratione, c. 8, and especially Epist. 190 to Innocent II against certain articles of the errors of Abelard, ch. 1. Before Abelard, a certain Mamertus — not the one who was bishop of Vienne, but a priest of the same church — had asserted, in de Statu animae, VIII, that Plato had divined the Most Holy Trinity by the powers of his own genius. After him, Raymond Lull was putting forward an argument of his own invention, by which he maintained that the divine Trinity could be made rationally evident. In the Trinity, he said, there is infinite posse, and consequently infinite possificans. But the infinite possificans of God necessarily produces in man a possificatum of the same nature. Therefore man finds in himself the notion of the Trinity. This Raymond was condemned by Gregory XI.

Proof 1° from authority. Matt., XI, 27, it is said: No one knows the Son except the Father; nor does anyone know the Father except the Son, and he to whom the Son wills to reveal him. In the same place, XVI, 17, Christ says to Peter, who professed his divine sonship: Blessed are you, Simon Bar-Jona, for flesh and blood has not revealed this to you, but my Father who is in heaven. And Pope Hormisdas, in Epist. 79 to Emperor Justin: «The secret of the Trinity no nature of visible or invisible things was able to investigate.»

Proof 2° from reason.² Nothing about God can we know through natural reason except from created effects; for we know nothing of God a priori and through a cause, since there is no cause of God or of the Trinity. But from created effects, at least natural ones, we cannot arrive at knowledge of so great a mystery. Therefore. — Proof of the minor. An effect, however perfectly known, does not lead to knowledge of the cause except under that aspect by which it proceeds from it and has an essential connection with it. Thus, e.g., an effect proceeding from a craftsman — say, a house from a builder — manifests indeed the art from which it essentially proceeds, and the man insofar as he is a craftsman, but not the other accidents of this man that do not pertain to his art, e.g., whether he was tall or short, white or dark, fat or lean, dressed in red or green, etc. But created effects do not proceed nor depend essentially on God as triune, but only insofar as he is one. Therefore. — Proof of the minor. Created effects proceed from God by reason of divinity as the radical cause, and by reason of omnipotence as the proximate cause. But omnipotence belongs to God prior to the relations by which the persons are constituted being able to be conceived, and pertains to the nature insofar as it is one, not insofar as it is triune in persons; for not each person has its own distinct omnipotence: whence it is commonly said that the works of the Most Holy Trinity ad extra are undivided. Therefore created effects do not proceed essentially from God as triune, but only concomitantly, insofar as the producing power is one and the same in the three. Whence if, per impossibile, God were not triune, creatures would nevertheless remain, because the power productive of them would remain.

From this you conclude, 1° that even granted faith, this mystery cannot be evidently demonstrated by natural reason alone, because divine revelation does not make creatures depend and proceed essentially from God as triune, nor does it place in creatures any trace of the Most Holy Trinity.

You conclude 2°, for the same reason, that not even the possibility of this mystery can be established by natural reason alone.

[You conclude 3° that, if a wayfarer-man were to know quiddidatively, that is, through essence, the beatific vision, the light of glory, the hypostatic union — which does not seem repugnant, since every created thing is knowable through its proper species — he would also evidently know the mystery of the Most Holy Trinity as to whether it exists, on account of the connection which those supernatural effects have with the Trinity, not indeed as cause, but as object or united term. Hence I said in the proof of the conclusion: from created effects, at least natural ones.]

If you object that certain pagan philosophers had some knowledge of the mystery of the Most Holy Trinity, I reply that they drew it not through natural reason from created effects, but either from the teaching and tradition of the Hebrews, some of whom, as we shall say below, knew this mystery through divine and personal manifestation, or from the reading of the Sacred Scriptures or the Sibylline books, or from divine revelation, as in the case of the Sibyls themselves, or even from the revelation of demons, who, before they fell, knew this mystery by divine illumination, and could have imparted knowledge of it to men, whether by God's command or out of malice, so that, by positing three persons, they might persuade men that there are three gods — whence Plato, who is said to have admitted the Trinity, also professed three gods.³

I say 2°: Granted faith, this mystery can be commended by various congruences and defended against opposing arguments. Hence it is commonly said that it is above, but not against reason.

Proof of the first part, by proposing various congruences: 1° from reason; 2° from examples; 3° from the ternary number.

From reason, the first congruence is drawn from the nature of the highest good, which is maximally diffusive of itself, and this maximum diffusion shines forth especially in the mystery of the Most Holy Trinity. — The second is grounded in the notion of friendship and society, which is congruently required for supreme happiness. But friendship and society require a number of equal persons; for there is no friendship or society between things of different species, e.g., between a man and a brute or a stone. — The third congruence is grounded in the fact that to beget one's like is a perfection. — The fourth, because in ourselves we experience a procession of word and love, which, since it can be purified of its imperfections, seems to have to be admitted in God. — The fifth congruence is proposed thus. A wholly infinite being, such as God is, must include every possible conceivable entity, and therefore both absolute and relative. But the relative requires a correlative distinct from itself, to which it is referred; for nothing is referred to itself. Hence these relatives, because they have relative opposition to each other, are really distinguished among themselves; but because they have no opposition with the absolute, they are really identified with it. Now relative opposition in God is grounded in origin, which is twofold, one through intellect, the other through will: hence there are three relatives, one unproduced and producing, two produced. We have therefore three relatives really distinct among themselves and identified in one absolute: and because these three relatives in God cannot be accidents, since accident involves imperfection, it follows that they are substances, and indeed persons, because by reason of their relation and correlation they are incommunicable.

From examples. First. In the rational soul there are found esse, nosse, velle. Likewise, in the same soul there are memory, intellect and will. So St. Aug., lib. XIV de Trinitate, c. 8, n. 11. — Second. In fire there are three things: motion, brightness and heat, and yet it is one fire. So St. Aug., serm. 384,⁴ n. 2. In a tree: trunk, branches and leaves, and yet it is one tree. — These examples, however, as St. Thomas notes elsewhere, have more dissimilarity than similarity.

From the ternary number. In the world, the whole universe consists of three genera of beings: being, living, understanding. The principle of natural beings is threefold: matter, form and privation. There are three parts of time: past, present and future. Three measures of duration: time, aevum, eternity. Three species of quantity: line, surface, body. Three dimensions of body: length, breadth, depth. In man, a threefold faculty: memory, intellect, will. A threefold operation: vegetative, sensitive, intellectual. A threefold operation of the mind: simple apprehension, judgment, discourse. In the angels, three hierarchies; in each hierarchy, three choirs; in each choir, a threefold operation: purification, illumination, perfection. Finally, in all creatures these three are found: unity, species and order. Likewise: one, true, good. Likewise: being, power and operation.

Hence the ternary number is so celebrated that by it we signify what we consider absolute over all numbers, as when we say, e.g., «thrice blessed,» and that saying of the poet: Numero Deus impare gaudet. For the ternary number contains all perfections, namely: the principle, which is unity; the species, which is duality; the complement, which is the third unity.

Proof of the second part. Whatever arguments are put forward against the documents of faith do not proceed from principles known by nature per se, and therefore do not have the force of demonstration, but are reasons either only probable or sophistical. Therefore a place remains for solving them. — Proof of the antecedent. The true is not contrary to the true, but only to the false. But principles known by nature per se are true, and likewise the documents of faith are most true. Therefore.

The same truth is proved by all the motives of credibility of the mysteries of our religion, of which in the treatise de Fide.

One may ask what knowledge of this mystery was granted to the Jews.

Reply 1°. To the patriarchs, prophets and those excelling in singular holiness, an open knowledge of this mystery was granted.

Proof 1° from Sacred Scripture. To the aforementioned was granted a notion, or explicit faith, of the Incarnation of the Word. But this presupposes an open knowledge of the Trinity, since Christ is the second uncreated person of the Trinity. Therefore. — Proof of the major from the desires of the saints of the Old Testament. Matt., XIII, 17: Amen I say to you, says Christ, that many prophets and just men longed to see what you see, and did not see it. And John, VIII, 56: Abraham your father rejoiced to see my day: he saw it and was glad. But this desire to see Christ presupposes knowledge of him.

Proof 2° from the Fathers. St. Ambrose, lib. I de Cain et Abel, c. 8, and St. Aug., lib. II de Trinitate, c. 11, n. 20, teach that Abraham recognized the Trinity when he saw three and adored one. Augustine says pointedly there: «When three men were seen, and none of them was said to be greater than the others in form, age or power: why should we not here understand that the equality of the Trinity was visibly suggested through a visible creature, and in three persons one and the same substance?» St. Epiph., Haeresi V: «One Trinity, he says, was always announced in that singular divinity and believed by those who excelled the others,» and of this kind were the prophets and men endowed with exceptional holiness. Likewise Cyril of Alexandria, Theodoret, and others.

Proof 3° from reason. The patriarchs and prophets themselves committed this mystery to writing, as we saw above in the proof of the truth of the mystery itself. Therefore they knew it.

Reply 2°. It is probable that certain scribes and experts in the law of the Jewish people were granted knowledge of this mystery.

Proof. Because this mystery is indicated for us in the Sacred Scriptures of the Old Testament. Nothing therefore prevents the doctors of the Jewish people, who scrutinized the Sacred Scriptures, from having seen it in them.

Reply 3°. According to the Fathers, knowledge of this mystery was not granted to the common people of the Jewish nation. So Tertullian, adv. Praxeam, c. 31; Theodoret, Serm. II de Graecis affectionibus; St. Greg. Naz., Orat. 37; St. Basil, lib. II contra Eunomium; St. Greg. of Nyssa, lib. de Imagine Dei; St. Chrysostom, hom. 5 de Incomprehensibili Dei natura, and others. For this economy several reasons were present, of which the chief is that the Jewish people, more prone to idolatry, were not capable of this mystery. «Since they had dwelt in Egypt for a very long time, says Theodoret at the place cited, and had there learned the worship of many gods after the Egyptian rite, the all-wise God did not hand down to them the mystery of the Trinity clearly in all its fullness, lest from it they should take occasion of a multitude of gods, being inclined toward the impiety of the Egyptians.» The other reason, put forward by Tertullian at the place mentioned above, is that a more perfect knowledge of divinity was to be reserved for the new law, as the nobler one, so that from this a clearer distinction between both laws might be had.

If you say that the Jewish people were granted faith in Christ, which presupposes knowledge of the Trinity, I reply that this people was granted implicit faith in Christ, but not explicit faith; for this was not required before the Incarnation, but implicit faith sufficed, which does not presuppose knowledge of a plurality of persons in God. [But that the common people of this nation did not explicitly know the Incarnation as something future is clear from the fact that the Jews wanted to stone Christ because he called himself God, and from the fact that they believed the Messiah would come as a temporal king, who would free his people from enemies and servitude by arms.]