Summa summae S. Thomae sive compendium theologiae

[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.]