Thomas Aquinas, Summa Theologiae

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 (Question 39, Article 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 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."

Articulus 1

Argumentum 1

Ad primum sic proceditur. Videtur quod aequalitas non competat divinis personis. Aequalitas enim attenditur secundum unum in quantitate, ut patet per philosophum, V metaphys..

In divinis autem personis non invenitur neque quantitas continua intrinseca, quae dicitur magnitudo; neque quantitas continua extrinseca, quae dicitur locus et tempus; neque secundum quantitatem discretam invenitur in eis aequalitas, quia duae personae sunt plures quam una.

Ergo divinis personis non convenit aequalitas.

Argumentum 2

Praeterea, divinae personae sunt unius essentiae, ut supra dictum est.

Essentia autem significatur per modum formae. Convenientia autem in forma non facit aequalitatem, sed similitudinem. Ergo in divinis personis est dicenda similitudo, et non aequalitas.

Argumentum 3

Praeterea, in quibuscumque invenitur aequalitas, illa sunt sibi invicem aequalia, quia aequale dicitur aequali aequale. Sed divinae personae non possunt sibi invicem dici aequales.

Quia, ut Augustinus dicit, VI de Trin., imago, si perfecte implet illud cuius est imago, ipsa coaequatur ei, non illud imagini suae.

Imago autem patris est filius, et sic pater non est aequalis filio. Non ergo in divinis personis invenitur aequalitas.

Argumentum 4

Praeterea, aequalitas relatio quaedam est. Sed nulla relatio est communis omnibus personis, cum secundum relationes personae ab invicem distinguantur. Non ergo aequalitas divinis personis convenit.

Sed Contra

Sed contra est quod Athanasius dicit, quod tres personae coaeternae sibi sunt et coaequales.

Corpus

Respondeo dicendum quod necesse est ponere aequalitatem in divinis personis.

Quia secundum philosophum, in X metaphys., aequale dicitur quasi per negationem minoris et maioris.

Non autem possumus in divinis personis ponere aliquid maius et minus, quia, ut boetius dicit, in libro de Trin., eos differentia, scilicet deitatis, comitatur, qui vel augent vel minuunt, ut Ariani, qui gradibus meritorum trinitatem variantes distrahunt, atque in pluralitatem deducunt.

Cuius ratio est, quia inaequalium non potest esse una quantitas numero. Quantitas autem in divinis non est aliud quam eius essentia. Unde relinquitur quod, si esset aliqua inaequalitas in divinis personis, quod non esset in eis una essentia, et sic non essent tres personae unus deus, quod est impossibile.

Oportet igitur aequalitatem ponere in divinis personis.

Ad 1

Ad primum ergo dicendum quod duplex est quantitas. Una scilicet quae dicitur quantitas molis, vel quantitas dimensiva, quae in solis rebus corporalibus est, unde in divinis personis locum non habet. Sed alia est quantitas virtutis, quae attenditur secundum perfectionem alicuius naturae vel formae, quae quidem quantitas designatur secundum quod dicitur aliquid magis vel minus calidum, inquantum est perfectius vel minus perfectum in caliditate. Huiusmodi autem quantitas virtualis attenditur primo quidem in radice, idest in ipsa perfectione formae vel naturae, et sic dicitur magnitudo spiritualis, sicut dicitur magnus calor propter suam intensionem et perfectionem.

Et ideo dicit Augustinus, VI de Trin., quod in his quae non mole magna sunt, hoc est maius esse, quod est melius esse, nam melius dicitur quod perfectius est. Secundo autem attenditur quantitas virtualis in effectibus formae. Primus autem effectus formae est esse, nam omnis res habet esse secundum suam formam.

Secundus autem effectus est operatio, nam omne agens agit per suam formam. Attenditur igitur quantitas virtualis et secundum esse, et secundum operationem, secundum esse quidem, inquantum ea quae sunt perfectioris naturae, sunt maioris durationis; secundum operationem vero, inquantum ea quae sunt perfectioris naturae, sunt magis potentia ad agendum.

Sic igitur, ut Augustinus dicit, in libro de fide ad Petrum, aequalitas intelligitur in patre et filio et spiritu sancto, inquantum nullus horum aut praecedit aeternitate, aut excedit magnitudine, aut superat potestate.

Ad 2

Ad secundum dicendum quod ubi attenditur aequalitas secundum quantitatem virtualem, aequalitas includit in se similitudinem, et aliquid plus, quia excludit excessum. Quaecumque enim communicant in una forma, possunt dici similia, etiamsi inaequaliter illam formam participant, sicut si dicatur aer esse similis igni in calore, sed non possunt dici aequalia, si unum altero perfectius formam illam participet. Et quia non solum una est natura patris et filii, sed etiam aeque perfecte est in utroque, ideo non solum dicimus filium esse similem patri, ut excludatur error eunomii; sed etiam dicimus aequalem, ut excludatur error Arii.

Ad 3

Ad tertium dicendum quod aequalitas vel similitudo dupliciter potest significari in divinis, scilicet per nomina et per verba.

Secundum quidem quod significatur per nomina, mutua aequalitas dicitur in divinis personis et similitudo, filius enim est aequalis et similis patri, et e converso. Et hoc ideo, quia essentia divina non magis est patris quam filii, unde, sicut filius habet magnitudinem patris, quod est esse eum aequalem patri, ita pater habet magnitudinem filii, quod est esse eum aequalem filio.

Sed quantum ad creaturas, ut dionysius dicit, IX cap. De div. Nom., non recipitur conversio aequalitatis et similitudinis.

Dicuntur enim causata similia causis, inquantum habent formam causarum, sed non e converso, quia forma principaliter est in causa, et secundario in causato. Sed verba significant aequalitatem cum motu. Et licet motus non sit in divinis, est tamen ibi accipere. Quia igitur filius accipit a patre unde est aequalis ei, et non e converso, propter hoc dicimus quod filius coaequatur patri, et non e converso.

Ad 4

Ad quartum dicendum quod in divinis personis nihil est considerare nisi essentiam, in qua communicant, et relationes, in quibus distinguuntur. Aequalitas autem utrumque importat, scilicet distinctionem personarum, quia nihil sibi ipsi dicitur aequale; et unitatem essentiae, quia ex hoc personae sunt sibi invicem aequales, quod sunt unius magnitudinis et essentiae.

Manifestum est autem quod idem ad seipsum non refertur aliqua relatione reali. Nec iterum una relatio refertur ad aliam per aliquam aliam relationem, cum enim dicimus quod paternitas opponitur filiationi, oppositio non est relatio media inter paternitatem et filiationem. Quia utroque modo relatio multiplicaretur in infinitum. Et ideo aequalitas et similitudo in divinis personis non est aliqua realis relatio distincta a relationibus personalibus, sed in suo intellectu includit et relationes distinguentes personas, et essentiae unitatem.

Et propterea magister dicit, in XXXI dist. I Sent., quod in his appellatio tantum est relativa.