God is one and yet God is three. In this simple statement of Trinitarian faith lays one of the greatest mysteries of Christianity. That it is true is a matter of faith and, Aquinas believes, it cannot be demonstrated on purely metaphysical grounds. Still, we can ask whether it can be considered coherent. Aquinas has identified that scripture reveals to us that there are real subsisting relations within the Godhead and that we can identify these with the “persons” identified in the creedal statements of the Church. Aquinas now focuses on the question of plurality in the Godhead with respect to the persons: is there plurality? How many persons are there in the Godhead? In what sense can we even think about using number when it comes to the persons of the Godhead?
The Thread of the Argument
A1: In the light of the Christian teaching on the unity and simplicity of God, the first question to ask is whether it makes sense to talk about a plurality of persons in God. Of course the Christian Tradition, here illustrated by the Athanasian Creed, insists upon such a plurality and Aquinas aligns his teaching with this. As the notion of “person” corresponds to a relation subsisting as a reality in the Godhead and as there are a plurality of such relations, then it makes sense to talk of a plurality of persons in God.
The reply to the first objection sees Aquinas continuing his explanation of the possibilities for confusion in the Greek and Latin terminology. The second objection asks why, when the absolute properties of God (such as goodness and wisdom) do not lead to differentiation, relations do lead to such distinctions. Aquinas recalls the fundamental difference between absolute and relative properties: the very being of relations is founded in their pointing to something else; they exist in opposition. It is this that creates the multiplicity from relations. Continuing this theme, for the third objection Aquinas points out that a plurality of absolute things (such as goodness, wisdom) does not create plurality in God because of His simplicity. But relations, because of their pointing-to-the-other, do not create the type of composition of thing-and-property that would contradict simplicity. Finally number, by its very definition, would seem to create parts-within-a-whole. Aquinas replies that, at the very least, we can attribute number as an intellectual construct to God because such a construct exists in the intellect rather than in the thing itself. He postpones until Question 42 Article 4 a discussion of why number existing in things (as when we count parts of a whole) does not pose a challenge when we apply it to the Trinity.
A2: Having accepted that we can reasonably talk about persons in the Godhead, we must continue the enquiry of Question 27 Article 5 and Question 28 Article 4 and check that Aquinas’s Trinitarian theory gives us the “right” number of persons. Aquinas argues that the real distinctions among the persons arise from their being in relational opposition to one another; therefore all he has to do is to count the genuine relation oppositions. The technical difficulty arises from the doctrine that the Holy Spirit proceeds from the Father and the Son (the famous filioque clause of the creed). Unless care is taken over the relational opposites associated with the Holy Spirit, there will be some double counting.
The relations to sort out are the spiration and the procession (the latter in the sense specialized to the Holy Spirit). First Aquinas points out that procession cannot be associated with the Father and/or the Son, since if this were so the relations of paternity and sonship (based on intellectual procession) would be founded on the procession of the will. Therefore procession is associated with the Holy Spirit and spiration is associated with both the Father and the Son. In the reply to the first objection, Aquinas goes a little bit further and explains that whilst paternity, filiation and procession are personal properties (i.e. they constitute the persons), spiration is not as it neither belongs to a single person nor constitutes a single person.
A3: When we talk about plurality or number in the Godhead we are faced with one of the central mysteries of the Trinity: how can there be just one God (who is absolutely simple) and yet there be these three “persons” in the Godhead. So far, we may have been unconsciously assuming that we apply the concept of number univocally to God and to creatures; but is this valid? What does it mean to apply number to God? Do numerical terms imply some reality in God?
Aquinas observes that the notion of plurality arises in two ways. On the one hand, material things can be divided into subsets and from this we associate number with quantity. On the other hand there is a transcendental notion of plurality that arises from dividing being into the one and the many. This latter is the only sort of plurality that makes sense for immaterial things. Aquinas claims that previous authors have become muddled on this issue by attempting to apply the first notion of number to God. Aquinas rejects this line of thinking, suggesting that if it is followed one can only make sense of numerical claims about God in terms of metaphor.
Aquinas therefore considers number as applied to the Godhead in terms of the transcendental notions of unity and multiplicity. Aquinas has already applied the transcendental notion of unity (convertible with being) to God’s essence in Question 11 Article 1: When we say that God is one, we are positively affirming that His being is an undivided reality. Here Aquinas applies transcendental multiplicity to the Godhead: what this affirms is that each person is undivided and that each person is not some other person. Put in this way, Aquinas claims that we can then affirm number to the Godhead as a reality and not just as a metaphor or simply as an intellectual construct. Moreover, as Aquinas lays out in his reply to the third objection, unity does not exclude multiplicity but rather excludes division. Similarly, multiplicity does not exclude unity but rather division between the realities out of which the multiplicity is formed.
A4: The final article in this question is a somewhat technical exploration of how the notion of “person” can be considered common to the three persons. That there might be a problem is explored in the objections: for example, only essence is common to the three persons, therefore personhood cannot be common to them. Similarly, if “person” is common to the three then it is either a real or conceptual commonality. If it is only a conceptual commonality then there is really only one person; if it is a real commonality then this would seem to set up “person” as being a universal with God possessing particularity, or genus and species, with respect to this universal (see Question 3 Article 5).
Aquinas points out that when we talk about creatures such as men, the name “person” is common to them, but it is a different sort of commonality than that implied by saying that they share the same essence. It is not a real commonality, but the type of commonality that it is has been something over which various authors have disagreed. Aquinas argues that this commonality is a commonality of concept, pointing towards the notion of an indeterminate individual (such as we refer to when we say “a man” without any particular man in mind). Even with this vagueness, in the example of “a man”, we point towards a common nature, together with a particular mode of existing as a per se individual. Now when we use the term “person” (as opposed to “a man”) things are slightly different: we are pointing towards a reality that subsists in a particular nature. This is what is conceptually common to all of the divine persons.
In answer to the objection against conceptual commonality, Aquinas points out that even when we consider creatures, commonality of personhood does not set up commonality of genus or species, so the objection fails. Moreover, things are simply different when we consider the divine: the persons share a common being whereas creatures particularizing a universal have different beings.
- “Persons” in the Godhead correspond to subsisting relations and therefore we can talk about a plurality of such persons.
- Spiration is a real relation in the Godhead but does not belong to or constitute a person; therefore the four real relations in the Godhead correspond to three persons.
- In considering number and plurality to arise out of the division of being into the one and the many, Aquinas is following Aristotle’s Metaphysics.
- The discussion of number as applied to the Godhead had rumbled on for many years during the middle ages. A good discussion of the background to Aquinas’s treatment can be found in Chapter 7 of Emery’s “The Trinitarian Theology of St. Thomas Aquinas”.
- In the sed contra of Article 2, Aquinas quotes the famous Johannine Comma as an authority in favour of the tri-personality of God. Although the canonicity of this writing is disputed, it can still be considered at the very least as an ancient authority.
- Aquinas’s reduction of the four real relations in the Godhead to the three persons may seem a bit of an ad-hoc sleight of hand to accommodate the filioque. However, one might note that the problem doesn’t simply go away if one insists that the Holy Spirit proceeds only from the Father, and even might be considered worse if this were the case. Having two real relations (paternity and spiration) associated with the Father would seem to associate two persons with the Father!
- In the de potentia (Q.9 A.5) Aquinas writes that “The plurality of persons in God is an article of faith, and natural human reason is unable to investigate and adequately understand it.” We emphasize again that Aquinas is not trying here to derive this truth of faith from reason but is trying to show that it is at least rationally coherent.
- The difficult notion of transcendental multiplicity is discussed at more length in Aquinas’s de potentia Q.9 A.7.