“Perichoresis” or, in Latin, circumincessio, has been a fairly traditional term in trinitarian theology since at least the time of John of Damascus. Before he applied it to the trinitarian issue, it was used to speak of the mutual interpenetration of the human and divine natures of Christ in the incarnation. But in trinitarian theology, it speaks of the mutual indwelling of the persons of the Trinity. Scripturally, the taproot of the doctrine comes in Jesus’ discourses in John where he says things like, “I am in the Father and the Father is in me” and so forth (John 14:10-11). The point is that there is a “reciprocal interiority” of Father, Son, and Spirit in that they exist within the other persons in an unconfused, but ineffable unity.

In recent theology the concept has become sexy and made to do a lot of work in broader theological systems. For instance, in the work of types like Jurgen Moltmann, the perichoresis of the persons has been used to secure the unity of the Trinity in a social doctrine of the Trinity, while at the same time speaking to the God-world relationship. Colin Gunton has expanded it out as a “transcendental” that allows us to understand the deep, interpenetrating structures of reality. People have developed spiritualities, political and economic programs, and even marital models out of it, leaving theologians like Karen Kilby to wonder if the process of projection hasn’t been at work here.

In any case, as I was reading Gilles Emery’s exposition The Trinitarian Theology of Thomas Aquinas, he draws attention to the Thomas’ doctrine of perichoresis as something of a synthesis of his trinitarian doctrine as a whole. Given its contemporary importance, it seemed worth reviewing what this giant of Western trinitarianism had to say on the subject.

To be begin, it might seem like he has little to say, simply because neither the Greek term “perichoresis” nor the Latin term “circumincessio” appear in Thomas. But Emery notes that while the specific terms may not appear, a battery of other phrases demonstrate that the concept is deeply rooted in Thomas’ thought:

In presenting the ‘in being’ of the persons, he uses, rather, the expressions ‘union or intrinsic conjunction’, ‘interiority’, ‘intimacy’, ‘existing in’, ‘being in that which is the most intimate and most secret’ (this is how the Son is in the Father), ‘reciprocal communality of “in being,”’ ‘communal union’, etc. In every case, the communal presence of the persons excludes their confusion, because it is based in their real distinction. It rules out the ‘isolation’ of one person, since it implies a communal relationship of persons. The divine persons are not ‘solitaries’: they are ‘inseparables’. (302)

With that linguistic point out of the way, Emery shows that for Thomas, the communal immanence of the persons rests three main bases: their consubstantiality, their relations, and the processions. I’ll try to briefly review them following Emery’s discussion (pp. 302-308).

To begin, following the Fathers, especially Hilary, Thomas places the unity of God’s nature, or the consubstantiality of the persons, front and center:

As to essence, the Father is in the Son because the Father is his essence and he shares it with the Son without any change taking place in himself; therefore because the Father’s essence is in the Son, it follows that the Father is in the Son. Equally, the Son being his own essence, it follows that he is in the Father, in whom the same essence is present. (ST I, q. 42, a. 5)

It’s not just that the persons share the same kind of nature. In fact, they share the same concrete nature. According to his doctrine of simplicity, we have to say that each of the persons are the divine nature. And so, “the nature of the Father is in the Son, and conversely, the Father is in the Son and reciprocally” (Commentary on John, 10.38). The mutual immanence of the persons, therefore, rests on their unity of nature.

Second, the relations also play a role. Emery suggests that Thomas follows John of Damascus by way of his teacher Albert the Great here. The point is that the in itself, the idea or notion of relations include an inherent mutuality. “Likewise as to the relations, it is clear that each of the relative opposites is in the notion of the other” (ST, I q. 42, a. 5). Less abstractly, as realities naturally relating to each other, the notions of “Father” and “Son” are mutually-implicated and included within the other:

In God, the Son is also properly in the Father from the perspective of relation—and that in a more fitting way than amongst human fathers and sons—because it is by his relation that the Son is a subsisting person: his relation is his personality. (I Sent. d. 19, q. 3, a. 2, ad 1)

As Emery highlights, “It is not just that a relative reality cannot be thought without its correlative. It cannot exist as such without it…” (304). For Thomas, persons are “subsistent relations”—the relations constitute the persons. And this is one of the features that distinguishes divine personality from other forms, and makes true reciprocal interiority an exclusively divine property.

Emery also highlights that their reciprocal interiority is not a flat one. At the level of the unity of nature, their interiority is the same. But when you look at it from the angle of the relations, their presence within each other implies a particular mode of relations, a mode of being which is distinct.

Which brings us to the third angle from which to consider perichoresis, which is that of the processions, or origin of the relations. In other words, the generation of the Son and the procession of the Spirit. Now, one might think that the notion of procession might disrupt perichoresis, since linguistically and even conceptually it implies a “going out.” But Thomas clarifies by distinguishing divine procession from material procession:

In material things, what comes forth from another is no longer in it, since it comes from it by a separation from it in essence or in space. But in God, coming forth does not arise in this way. The Son came forth eternally from the Father in such a way that the Son is still in the Father from all eternity. And so, when he is in the Father, he comes forth. And when he comes forth, he is in him, in such a way that he is always coming forth, and always in him. (Commentary on John, 16:28)

It’s important to remember that Thomas follows after Augustine in thinking through the processions on analogy of mental self-presence. The Son is the mental Word which is conceived and dwells in the mind of the Father. Also, as the Love or bond between the Father and Son, the Spirit dwells within both from whom he proceeds. And so the eternal processions, along with the relations, and the consubstantiality of the persons ground their unity, their distinctness, and their mutual indwelling precisely as eternal Father, Son, and Spirit.

Now, in context, Emery is keen to show in his analysis the way Thomas developed the mutual indwelling of the persons in Thomas in order to combat the dual errors of Sabellianism and subordination, as well as develop the notion of trinitarian action. The analysis is helpful and worth consulting, since I’ve only given a thumbnail sketch here.

What struck me, though, is the way that perichoresis is treated as a summary doctrine built upon and tying together the other threads of consubstantiality, relation, and procession. In Thomas, (and arguably the Fathers whom he follows) perichoresis is the fruit of the three other notions, not their foundation.

This appears to be a valuable approach towards thinking about and deploying the concept of perichoresis. In the first place, it helps pump the brakes against certain expositions treating perichoresis as a stand-alone formula or mechanism, which is supposed to do all the work in trinitarian theology. Trinitarian dogmatics cannot live by perichoresis alone. On the other hand, some of us may therefore be tempted to downplay, or ignore the concept by way of reaction against those formulations. To those, Thomas can help us see its place as a crowning summary concept, allowing us to appreciate the beautifully unifying the whole, and worship more fully the One who is Three and the Three who are One.

Soli Deo Gloria