Summa summae S. Thomae sive compendium theologiae

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.