Divine Persons and Notional Acts in the Trinitarian Theology of Thomas Aquinas

Medieval Trinitarian Terminology as Interpreted by Thomas Aquinas

Probably the single greatest obstacle to the contemporary retrieval of medieval trinitarian theology is its highly technical terminology. It is filled with metaphysical and philosophical presuppositions foreign to most people today and is difficult even for professional theologians to access. Complicating matters further is the fact that the same terms can be used with subtle, but significant, differences in meaning. Accordingly, there is considerable confusion and disagreement in the secondary literature on Thomas Aquinas about what he means by the term notional act. In particular, there is great disagreement about whether he recognizes four notional acts or only two—a question of considerable importance for his understanding of the notional acts. Yet this confusion and disagreement is rarely noted or even addressed. Consequently, before turning to the question of how Aquinas relates the Divine Persons to their notional acts, which is the principal interest of this article, it is necessary to provide an overview of his interpretation of medieval trinitarian terminology, and also to clarify how many notional acts he thinks there are.

Following patristic custom, medieval theologians attribute relations to the Divine Persons. Three relations are proper to a single Person only: the relation of paternity, proper to the Father and directed to the Son; the relation of filiation, proper to the Son and directed to the Father; and the relation of procession, proper to the Spirit and directed to Father and Son. These three relations are sometimes called personal relations. Then there is a fourth relation: the relation of common spiration, also known as active spiration, which belongs to both the Father and the Son and is directed to the Holy Spirit. These relations do not subsist between Persons. In the typical modern understanding of a relationship, a relationship is a common reality shared by two or more people. Trinitarian relations, however, are different. They are Aristotelian relations. They are properties. For example, the Father has the relation of paternity, which means that he relates to the Son as Father. The Father’s relation of paternity is not common to Father and Son, nor is it a tertium quid “between” Father and Son. It is proper to the Father, and only to the Father, even though it is directed to the Son. Aquinas embraces this tradition and assigns the four relations to the three Divine Persons accordingly. ¹⁵

In addition to the four relations, Aquinas also lists five notions. Sometime in the twelfth century, theologians began to speak of notions. ¹⁶ Notions are ideas by which the Divine Persons are known. ¹⁷ Notions include relations, but they also include the property of unbegottenness (innascibility) proper to the Father. For some time, it was debated how many notions there were, and, in the process, what exactly a notion consisted of. The view that became standard—which is also Aquinas’s view—is that there are five notions: the four relations plus the property of unbegottenness. ¹⁸ This settled enumeration implicitly clarified the meaning of notion. It also more firmly established the technical terms of paternity, filiation, procession, common spiration, and unbegottenness in medieval trinitarian theology.

In addition to the five notions, medieval theologians also speak of four intratrinitarian activities, which correspond to the relations like verbs to nouns. ¹⁹ To the Father is assigned generation, also known as active generation; to the Son, nativity, also known as passive generation; to the Spirit, procession, also known as passive spiration; to Father and Son together, spiration, also known as active or common spiration. ²⁰ The term generation denotes the Father’s generating of the Son; the term nativity denotes the Son’s coming forth from the Father; the term procession denotes the Spirit’s coming forth from Father and Son; the term spiration denotes the Father’s and Son’s spirating of the Holy Spirit. (Very confusingly, the terms spiration and procession are the same terms used for the relations of common spiration and procession.) By the time of Aquinas, these terms had become standard for talking about the intratrinitarian activities attributed to the Divine Persons.

That much is clear. What is not clear, however, is how medieval theologians classified generation, nativity, procession, and spiration. They all agreed that paternity, filiation, procession, and common spiration were relations. And they all agreed that paternity, filiation, procession, common spiration, and unbegottenness were notions. But what were generation, nativity, procession, and spiration? Among medieval theologians, there is no single category for all four that claims widespread consensus, at least in terms of explicit endorsement. In fact, at least until Thomas Aquinas, medieval theologians rarely even hint at one. They do, however, agree about some things. They agree that nativity and procession can be classified as origins: the way by which the Son and the Spirit receive their respective identities. They agree that nativity and procession can also be classified as processions: the way that the Son and the Spirit come forth from their respective principles (with the Son’s principle being the Father, and the Spirit’s principle being the Father and the Son together). ²¹

Medieval theologians also agree on another point. Beginning in the thirteenth century, after the terminology of notions had been well established, some theologians also speak about notional acts. ²² Notional acts are acts associated with the notions, and therefore individual Divine Persons. Beyond that, the category of notional act is not well defined. Among those theologians who use the term notional act, there is little consensus about its meaning and proper usage. Nevertheless, they agree on one important point: generation and spiration can be classified as notional acts.

But apart from these points of agreement, medieval theologians give mixed indications. Should the categories of origin and procession be taken to include generation and spiration (in addition to nativity and procession)? And should the category of notional act be taken to include nativity and procession (in addition to generation and spiration)? The answer is not immediately apparent. For example, medieval theologians often speak of origins in a generic way that clearly includes nativity and procession, but may or may not include generation and spiration. For the most part, medieval theologians do not attempt to clarify which intratrinitarian activities fall under the categories of origin or notional act. They simply talk about them in the course of addressing some topic in trinitarian theology. They rarely discuss how they should be classified.

On a few occasions, Thomas Aquinas makes an effort to explain his understanding of how these four intratrinitarian activities to relate to each other and other trinitarian categories. In question 40 of the Prima Pars of the Summa Theologiae, in the course of explaining why the Divine Persons are constituted by relations not origins, he states that origins can be understood from either an active perspective or a passive perspective. ²³ Taken actively, the category of origin encompasses generation and spiration. Taken passively, the category of origin encompasses nativity and procession. Elsewhere, in the Compendium Theologiae, he states that common spiration and procession, as well as generation and nativity, all signify origin. ²⁴ Based on these passages, it is clear that, for Aquinas, each of these four intratrinitarian activities can be classified under the category of origin.

What Aquinas says about origins seems to apply to processions as well. On multiple occasions, Aquinas speaks of “origins or processions” in a way that implicitly equates origins with processions. ²⁵ It is easy to understand why Aquinas equates origins and processions. If origins are the way by which Divine Persons receive their identity, and processions are the way that Divine Persons come forth from their respective principles, then of course it makes sense to equate origins with processions. The terms origin and procession each signify the same reality. The concept of origin puts the emphasis on how Divine Persons receive their identity, while the concept of procession puts the emphasis on how those same Divine Persons come forth from their principles, but both origin and procession signify the same reality. And if origin and procession signify the same reality, it follows that, for Aquinas, processions can also be understood from either an active or a passive perspective, just like origins. ²⁶ In fact, in one place in his Sentences commentary, he uses the expression passive procession. ²⁷ His use of this term implies that there is also such a thing as active procession. And if there is such a thing as active procession, then clearly procession can be understood either actively (from the perspective of the Father and the Son) or passively (from the perspective of the Spirit). Elsewhere he confirms this implication by stating that the terms spiration and procession each pertain to the “processions or origins.” ²⁸ For Aquinas, then, the category of procession, like the category of origin, has a double aspect, in that it can be understood either actively or passively. The category of procession does not apply merely to the Son and the Spirit coming forth from their respective principles; it also applies to the Father generating the Son, and to the Father and the Son together spirating the Spirit.

Like the categories of origin and procession, the category of notional act has a double aspect, too, both active and passive. Most of the time, Aquinas applies the category of notional act in an active sense, either to the Father generating the Son, or to the Father and the Son together spirating the Spirit. Yet he also implicitly classifies nativity and procession as notional acts. In one passage, Aquinas describes the Son’s receiving of the divine essence from the Father as a notional act, ²⁹ and in another he implies that generation and nativity are each equally notional acts. ³⁰ Likewise, in a couple of other passages, he refers to the Spirit’s procession as a notional act. ³¹ He also says that the Holy Spirit “proceeds as a subsisting operation,” ³² a phrase that implies that the Spirit’s proceeding is a kind of act. Individually and together, these passing comments all suggest that, for Aquinas, it is not merely generation and spiration that can rightly be classified as notional acts but also nativity and procession.

There is another reason to think that, for Aquinas, the category of notional act includes nativity and procession and not just generation and spiration. In his commentary on the Sentences, he explains that there are not two operations in the Father’s generation and the Son’s nativity, but only one. “By one and the same operation,” he writes, “the Father generates and the Son is born; but this operation is in the Father and the Son differently according to their respective relations.” ³³ For Aquinas, generation and nativity are not two distinct operations; they are the same operation from two different perspectives. By implication, the same must be true of spiration and procession. And if spiration and procession are one and the same operation from different perspectives, then they must each also be acts—or more precisely, notional acts.

Aquinas makes a clarification about the Son’s generation that bolsters this conclusion. In the Summa Theologiae, he explains that when we speak of the Son being generated, we must understand any implied passivity in a “grammatical” sense only, according to the way we talk about the Son’s generation, and not in the sense of moving from potency to act. ³⁴ Since God is pure act, there can be no metaphysical passivity in the Son’s nativity or the Spirit’s procession. Only one conclusion is possible: that both nativity (passive generation) and procession (passive spiration) are acts, too. ³⁵

For a variety of reasons, then, we have good grounds to conclude that, for Aquinas, the categories of origin, procession, and notional act designate the same realities in God. Yet this conclusion stands in some tension with the way Aquinas usually talks. Most of the time when he speaks about origins and processions, Aquinas seems to have in mind the coming forth of a Person from his principle, and, therefore, either nativity or procession. ³⁶ Likewise, when Aquinas speaks about notional acts, he usually seems to have in mind the acts proper to the principle of a procession, namely generation and spiration. ³⁷ And when it comes to the question of how many notional acts there are, he gives mixed signals. Sometimes he seems to classify generation, nativity, spiration, and procession as four distinct notional acts. On other occasions, he speaks as though there are only two origins, processions, or notional acts. In the Summa Theologiae, for example, he states that there are only two actions in God, namely the action of the intellect and the action of the will, and that, as a result, there are only two processions, namely the procession of the Word and the procession of love. ³⁸

The tension between Aquinas’s definitions of key terms and his actual use of them reflects larger tensions in medieval theology. Medieval theologians, like theologians today, never sat down to agree to any conventions about how they would speak about the Trinity. They just spoke about the Trinity with the vocabularies that they had inherited, and in conversation with each other, they gradually refined those vocabularies and settled on ways of speaking that allowed them to communicate, however imperfectly. The result was a functional, but not entirely consistent, terminology. Despite Aquinas’s evident interest in formulating systematic definitions and developing grammatical rules for using terms consistently, he is constrained by his inherited vocabulary. There is only so much order he can inject into linguistic conventions that arose organically, and not by design.

Aquinas’s lack of consistency explains the confusion and disagreement in the secondary literature about his theology of notional acts. In the secondary literature, scholars generally agree that, for Aquinas, processions, origins, and notional acts all somehow signify the emanation of the Son and the Holy Spirit from their respective principles. But they differ about whether these expressions signify the same realities in God. Some hold that notional act means the same thing as procession. ³⁹ Others hold that these two terms denote two separate categories, with notional acts relating to processions like action to passion. ⁴⁰ Interpreters also disagree about the number of notional acts. Some speak of two notional acts. ⁴¹ Others count four: generation (active generation) and nativity (passive generation), and then spiration (active spiration) and procession (passive spiration). ⁴² Still others speak of two notional acts: generation and spiration, but then specify that each notional act has a double aspect, such that generation and spiration can be considered from either an active perspective or a passive perspective. ⁴³

Having considered the conflicting evidence, we can easily account for this diversity of opinions among interpreters of Aquinas. Does he hold for two notional acts or four? Are processions, origins, and notional acts all the same thing, or do the terms procession, origin, and notional act refer to different realities in God? Aquinas is not entirely consistent. As a result, a variety of answers to these questions can claim good textual support. But on balance, if we pay particular attention to how he defines terms and the architectonic structure of his trinitarian metaphysics, we have good grounds to conclude that, for Aquinas, generation, nativity, spiration, and procession can each be classified as notional acts (whether that implies four notional acts, or two notional acts that can be considered from either an active or passive perspective), and that most of what he says about processions and origins applies to notional acts, and vice versa.

Father, Son, and Holy Spirit and Their Notional Acts

It is well known that, according to Thomas Aquinas, the Divine Persons are subsisting relations: that is, relations that subsist in and of themselves and not as accidents of some other substance. ⁴⁴ What is not as well known is that, for Aquinas, the Divine Persons are also, in reality, their respective notional acts. The way we talk and think about the Divine Persons differs from the way we talk and think about their respective notional acts, but they are ultimately one and the same thing. Divine Persons and their respective notional acts differ “according to mode of signification” (secundum modum significandi) or “according to mode of understanding” (secundum modum intelligendi), but in reality (in the res, in the thing), they are the same. The Father is generation, the Son is nativity, and the Spirit is procession.

Speaking of the Father, Aquinas explains, “Just as God’s act of understanding is God himself understanding, so the Father’s act of begetting is the begetting Father himself, although the modes of signifying are different.” ⁴⁵ The same applies to the other Divine Persons. Just as the Father is an act, the Son and the Spirit are acts, too. The Son is the act of proceeding from the Father, and the Holy Spirit is the act of proceeding from the Father and the Son. ⁴⁶ The reason for this identity between Person and action is, ultimately, divine simplicity. If there were a real distinction between Person and action in God, then action would be an accident, and divine simplicity rules out there being any accident in God. ⁴⁷

For similar reasons, Aquinas holds that, in reality, notional acts are identical with the corresponding relations. “Notional acts and the relations of Persons differ according to mode of signification, but in reality, they are entirely the same.” ⁴⁸ Notional acts differ from relations according to understanding and mode of signification, but they are the same in the sense that matters most: in actual, objective reality. Elsewhere, using the terminology of origins rather than notional acts, he makes a similar point. He explains that relations and origins are the same in reality, but relations signify “by way of form” while origins signify “by way of act.” ⁴⁹ The identity of relations and notional acts follows naturally from thinking of the Divine Persons as Aristotelian relations. For within the Trinity, relations imply processions, or more precisely, the Aristotelian categories of action and passion; with creatures, relations can be explained otherwise, but within God, only procession can explain relation. ⁵⁰ The relation of paternity, for example, implies generation. The Father’s relation to the Son as Father implies that the Father generates the Son. And due to the divine simplicity, anything attributed to a Divine Person must be identical with anything else attributed to that Person. So generation must be identical with paternity, and vice versa.

Compared to his contemporaries Alexander of Hales and Bonaventure (though not Albert) and many of his successors (notable exceptions including Henry of Ghent, John Duns Scotus, Dionysius the Carthusian), Aquinas stands out for how frequently he talks about notional acts. ⁵¹ This fact suggests that, compared to his contemporaries, he found the metaphysical category of act particularly useful when it comes to understanding the Divine Persons. Nevertheless, in asserting the ultimate identity of Persons, relations, and origins, Aquinas is not being innovative. He is asserting something held universally by his contemporaries. ⁵² The difference is that he also frequently invokes the category of notional act, which was just beginning to appear as a rough synonym for the category of origin, and thus extends the identity of Persons, relation, and origins to include notional acts as well. Bonaventure, for example, makes similar claims as Aquinas about the identity of Persons and origins. In the context of explaining how personal properties distinguish the Divine Persons from each other, Bonaventure explains that “in Divine Persons, ‘to originate,’ ‘to be,’ and ‘to refer to another’ are all the same,” but we can distinguish between them according to our mode of understanding. ⁵³ Later, he applies this principle to God the Father. He maintains that paternity and generation “are the same property in reality (secundum rem),” but this same property can signified in different ways. ⁵⁴ On these points, there is no substantive difference between Bonaventure and Aquinas. They agree that the Father and the act of generating differ according to mode of signification; they also agree that, in reality (in the res), the Father and the act of generating are one and the same.

Beyond these points of agreement, however, Aquinas takes a position that differentiates him from Bonaventure. ⁵⁵ He holds that the Divine Persons are “constituted” not by origins or notional acts but by relations. ⁵⁶ More specifically, they are constituted by personal relations (that is, paternity, filiation, or procession). ⁵⁷ What he means by this claim is not entirely clear because Aquinas is not entirely clear about what it means to constitute a Divine Person in the first place. ⁵⁸ Nor does he explain how constituting differs from distinguishing. ⁵⁹ To constitute a Divine Person is to make him who he is; beyond that it is difficult to say more. But it is clear that, for Aquinas, relations have a conceptual priority over origins. Even though relations and origins denote the same thing in God, they differ in mode of signification. And according to Aquinas, the mode of signification proper to relations is suited to the Divine Persons in a way that the mode of signification proper to origins is not. Consequently, relations can be said to constitute the Divine Persons, but origins cannot. In taking this position, Aquinas is following his teacher, Albert, who held that the Father’s generation of the Son presupposes a distinct Person; therefore paternity precedes generation. ⁶⁰ His position on this point will be vigorously defended by many theologians, especially Dominicans, and strenuously criticized by others, especially Franciscans. ⁶¹

In light of the controversy that follows him, which hardens as the years pass, it is notable that Aquinas’s position on the constitution of Divine Persons evolves over the course of his life. In his earlier writings, he emphasizes the priority of relation emphatically. He argues that the Persons are distinguished only by relation, and he does so without mentioning mode of signification or mode of understanding. ⁶² Later, his position softens, and he makes qualifications. ⁶³ Quite possibly in response to Bonaventure, he concedes that, according to the order of understanding, origin does precede relation in the case of the Son. ⁶⁴ More significantly, he acknowledges that Persons are distinguished by origins as well as relations. He says that both relations and origins distinguish the Persons, but that “it is better to say that the Persons or hypostases are distinguished by relations than by origins” because the ratio of origin “signifies the way to a subsisting Person, and not yet as constituting it.” ⁶⁵ Despite these concessions, however, he remains true to his original intuition about the priority of relations over origins. He never wavers in his position that it is relations, and not origins, that “constitute” the Divine Persons. ⁶⁶

In explaining his position, Aquinas offers two main arguments. First, he acknowledges that relations and origins are ultimately the same in God, but he points out that relations signify “by way of form” while origins signify “by way of act.” ⁶⁷ Accordingly, relations express something intrinsic to the Persons, whereas origins express something extrinsic: namely, the way from something or the way to something. For example, the Son’s nativity “signifies the way to a subsisting Person, and not yet as constituting it.” ⁶⁸ Consequently, relations are suited to signifying the Divine Persons in a way that origins are not. Second, Aquinas notes that “an action presupposes an acting Person.” ⁶⁹ Even though Persons and notional acts are the same in reality, they are not the same according to our mode of understanding. Therefore, according to our mode of understanding, notional acts presuppose Persons. ⁷⁰

Aquinas’s position is puzzling. The idea that relation and origin could differ according to mode of signification, but in reality be the same, is not the puzzling part. It is widely held, for example, that God’s goodness and God’s wisdom differ in the way we think and talk about God, but in God himself, due to divine simplicity, God’s goodness and God’s wisdom are actually one and the same thing. But Aquinas goes beyond asserting that relation and origin differ according to mode of signification but in reality are the same. He also says that the Divine Persons are constituted exclusively by relation. It is difficult to fathom how this claim could be true. If relations and origins are the same in reality, then it follows that origins constitute the Divine Persons—make them what they are—just as much as relations. To deny this would be like saying that God’s goodness, but not his wisdom, makes God who he is, which makes no sense. If God’s goodness and God’s wisdom are the same in reality, they must both equally make God who he is.

William of Ockham raises a similar objection. In his commentary on the Sentences, Ockham accurately summarizes Aquinas’s position and then responds to it. ⁷¹ In his response, he rejects the idea that modes of signification are relevant to the question of whether origins or relations constitute Divine Persons. “We cannot say,” Ockham writes, “that origin does not constitute, and relation does constitute, on the grounds that they differ according to modes of signification.” ⁷² Since origins and relations are the same in reality, if relations constitute Persons, then origins constitute Persons and vice versa. Modes of signification have no bearing on the matter because modes of signification are proper to signs, not things. ⁷³ And since Ockham agrees that relations and origins are the same in reality, he naturally concludes, against Aquinas, that origins, as well as relations, distinguish and constitute the Divine Persons.

It is difficult to see how Aquinas’s position could overcome Ockham’s objection. His claim that relations constitute Divine Persons, but origins do not, is not logically coherent. ⁷⁴ The root problem seems to be Aquinas’s understanding of signification. According to E. J. Ashworth, the theory of language that Aquinas shares with his contemporaries “tends to take words as units, endowed both with their signification and their modi significandi before they enter sentences and independently of speaker intention on any given occasion.” ⁷⁵ This approach to signification works well in a great variety of contexts, just as Newtonian mechanics works well with speeds not approaching the speed of light. Nevertheless, intention is intrinsic to words, ⁷⁶ and while Aquinas is sensitive to authorial intention when it comes to interpreting texts, ⁷⁷ his inherited theory of signification does not give adequate attention to speaker intention. Consequently, the theory is liable to break down in contexts where subtle shifts in intention change the meaning of words. That seems to be what is happening here. Aquinas seems to take the terms relation and origin to have a fixed mode of signification that transcends context or speaker intention. He also seems to treat their corresponding concepts as though they consist of mental representations. The problem is that words do not signify meaning apart from context and speaker intention. Moreover, mental concepts are not mini-models of external realities, but rather the medium through which we know the world, or in this case God. ⁷⁸ In his claim that relations, but not origins, constitute the Divine Persons, Aquinas confuses the order of signification with the order of reality. He fails to see that, by maintaining that relations and origins are the same in reality, he has committed himself to the view that origins, as well as relations, constitute the Divine Persons.

Putting aside these criticisms, we might well want to ask, Why does Aquinas fight so forcefully for the conceptual priority of relations over origins, when he concedes that, in reality, relations and origins are the same? Why does he care? A large part of the answer traces back to Peter Lombard’s Sentences. In book 1, distinction 27, Peter Lombard asks whether the Father is the Father because he begets or instead begets because he is the Father. Due to the influence of the Sentences, and the fact that theologians everywhere were required to teach from it and comment on it, this question was forced on theologians. Even when they made distinctions, as they usually did, the very process of answering the question encouraged them to think in binary terms and, as a result, to argue for the conceptual priority of either relations or origins. Battle lines were quickly drawn, and it became one of the great controversies of medieval trinitarian theology. ⁷⁹ With theologians long divided on this question by the time he started teaching, it would have been natural for Aquinas to assume that he had to take sides and very difficult for him to recognize that Lombard’s question was poorly framed and theologically misleading. It would also have been natural for Aquinas to favor relations over origins, as that was the position of his mentor, Albert. But whatever his precise reasons for emphasizing the conceptual priority of relations, it is striking that, as he grew older, Aquinas made more and more concessions to those who prioritized origins over relations—raising the possibility that, if he had lived longer, he may have made even more.

Explaining the Poor Reception of Aquinas’s Theology of Notional Acts

Probably for most theologians today, even for those with more than a passing acquaintance with the theology of Thomas Aquinas, it would likely come as a surprise to hear that, for Aquinas, the Divine Persons are, in reality, identical with their respective notional acts. Or that in taking this position, he was not proposing anything novel but simply echoing a commonplace of medieval theology about Persons and origins being identical with each other. And yet, the facts speak for themselves.

The idea that Father, Son, and Holy Spirit are, in reality, identical with their respective notional acts has no small significance—either in itself or in its implications. Why has this critical element of Aquinas’s trinitarian theology been so poorly recognized? How could it have been missed? There are many reasons. There is, first of all, the problem of his inherited terminology and his limited success in repurposing it to suit his theological ends. In conventional connotation and his own usage, notional acts were strongly associated with active generation and active spiration. Despite holding that nativity and procession can also be classified as notional acts, Aquinas never states his position clearly and unambiguously; their status as notional acts has to be inferred from passing comments and the internal logic of his system. Moreover, despite clarifying that, when we speak of the Son being generated, any implied passivity must be understood in a “grammatical” sense only, ⁸⁰ and thus tacitly qualifying the meaning of conventional terms like passive generation and passive spiration, Aquinas still continues to use this conventional terminology. By doing so, Aquinas obscures his commitment to the view that nativity and procession are, metaphysically, acts. ⁸¹

Having said that, the most decisive reasons for the poor reception of his theology of the notional acts do not lie in his terminology. They stem from his confusing distinctions about modes of signification and his commitment to false controversies about relations and origins, which muddy the waters and weaken the force of his metaphysical claims about the identity of Persons and acts. The sheer amount of attention that he gives to these issues, combined with the logical incoherence of his position and the subtle nature of his errors, distract greatly from what is most interesting and most significant about his theology of the notional acts—namely, his thoughtful elaboration of the view that the Divine Persons are, in reality, the same as their respective notional acts.

Things only got worse after his death. Due to the way that the Dominican tradition quickly united around him (something without parallel in the Franciscan tradition), and due to the tendency of the Franciscan tradition to define itself against the Dominican tradition, and vice versa, his problematic distinctions became perpetually frozen in theological discourse. ⁸² As his followers defended his distinctions, often with less suppleness and nuance than he did, his critics dug in their heels and became more extreme in their criticisms. To this day, the controversy about whether relations or origins constitute the Divine Persons has never been resolved, nor has there been any wide recognition that the controversy is a false one. Instead, it has mostly been forgotten. Like many forgotten controversies, however, it has not ceased to be influential—in this case, by obscuring what all medieval theologians believed in common and by burying deep in the tradition a false dichotomy between relations and origins. The hidden influence of this unresolved controversy has made it all the more difficult to appreciate the full significance of Aquinas’s view—shared by every one of his contemporaries—that, in reality, Divine Persons, relations, and origins are all the same.

Contemporary Applications

Once we strip away his confusing distinctions about modes of signification, Aquinas’s understanding of the notional acts opens up great possibilities for a better reception of his own theology and also for trinitarian theology more generally.

First, the idea that Divine Persons and their respective notional acts are one and the same supplies a very useful metaphysical category for thinking and talking about Father, Son, and Holy Spirit. In contemporary trinitarian theology, only a handful of metaphysical categories are ordinarily applied to Father, Son, and Holy Spirit: person, hypostasis, and relation. These are the only categories widely used to describe who and what they are. But the theology of Thomas Aquinas, and medieval theology more generally, give us good reasons to add a fourth: act. Father, Son, and Holy Spirit are not merely Persons, hypostases, and relations. They are eternal acts, too. ⁸³

Human language falls infinitely short of divine realities, and no human word, no human category, can ever do them justice. We therefore need a range of words to speak about the Trinity. Words communicate insight into divine realities only through metaphor and analogy, and the more metaphors and analogies at our disposal, the more we can play them off against each other to triangulate our meaning and better convey the truth about God. The category of act draws our attention to the dynamism and eternal liveliness of each Divine Person in a way that the categories of person, hypostasis, and relation do not. It puts the eternal activity of the Divine Persons front and center. It draws attention to the connection between persons and processions. ⁸⁴ It also clarifies that the Son’s generation is an eternal generation, without beginning or end, and that the Spirit’s eternal procession likewise has no beginning or end.

In this way, the metaphysical category of act is a very useful complement to the metaphysical category of relation. With too much emphasis on relation, the Trinity becomes static and lifeless; with too much emphasis on act, the Trinity becomes unstable and seemingly in a process of temporal becoming, which runs against divine eternity and diminishes the coequal dignity of the Son and the Holy Spirit. By balancing out the emphasis on relations that has long characterized the Western tradition, attention to the category of act makes the Western tradition more accessible to Eastern theologians who do not share this emphasis and who tend to emphasize the distinct origins of the Divine Persons: the Father as without origin, the Son as generated, and the Spirit as proceeding. ⁸⁵ It does all of these things without abandoning traditional Western theologies or terminologies. Affirming that the Father is an eternal act, for example, does not contradict the idea that he is also the relation of paternity. It simply supplies a complementary vantage point from which to contemplate who the Father is.

Second, thinking of the Holy Spirit as identical with his own act of proceeding counters portrayals—or implicit portrayals—of the Holy Spirit as entirely passive within the Trinity. Although he receives his deity, he does not receive it in a passive way. He is the act of proceeding; there is no metaphysical passivity in him. Granted, not everyone objects to passive portrayals of the Holy Spirit. Walter Kasper, for example, calls him “pure reception, pure gift,” and in contrast to the Father and the Son who are givers, he describes the Holy Spirit as “pure recipient.” ⁸⁶ But for those who regard such passive portrayals as problematic, or at least incomplete, thinking of the Holy Spirit as the act of proceeding provides a welcome alternative and one that can claim the theological authority of Thomas Aquinas.

Third, thinking of Divine Persons as acts can help correct against dyadic formulations that define the identities of Father and Son exclusively in terms of each other. While it is true that, properly understood, the relations of paternity and filiation imply the Holy Spirit, proper understanding is not easy to come by. Trinitarian theology is difficult, and Aristotelian ways of thinking about relation are foreign to contemporary modes of thought. It requires significant philosophical background to grasp what Aquinas means when he says that the Father is constituted by paternity. Thinking of the Divine Persons as acts comes more easily to us. And just as we intuitively recognize that the same action can have multiple effects in the human realm, we can readily imagine how a single, eternal act might have multiple effects. By the single, eternal act proper to himself, the Father does not merely generate the Son; with the Son, he also spirates the Spirit. His action has two effects. And since the Father is identical with his own proper act, he is accordingly constituted as Father not merely by his generating of the Son, but also by his spirating the Spirit. We speak of his generating and spirating as though they are two different acts, but actually, they are two different effects of the same eternal act. The same applies to the Son. By the single, eternal act proper to himself, the Son actively receives his deity from the Father and, with the Father, spirates the Spirit. We speak of the Son’s nativity and spirating as though they are two different acts, but in reality, they are two different effects of the same eternal act. Robert Doran makes a similar point: “for the Father to beget the Son and for the Son to be begotten of the Father is for the two together to breathe the Holy Spirit. The entire system of exchanges in God is an eternal blaze of love.” ⁸⁷ Granted, thinking of the Divine Persons as acts does not eliminate the lure of dyadic formulations. Dyadic formulations will always be tempting. In our human experience, we have strong human analogues for the Father and the Son but not for the Holy Spirit. As a result, it is easy to fall into thinking that we can grasp the identities of Father and Son without reference to the Holy Spirit. Thinking of the Divine Persons as acts provides an important resource for countering dyadic formulations. It opens up avenues for explaining how the Holy Spirit is, in fact, integral to the personal identities of both the Father and the Son.

Conclusion

Thomas Aquinas gave more attention to the category of notional act than any of his predecessors. In a sophisticated way, he integrated what was then a relatively new category with the more established terminology of origins and processions. Unfortunately, the ambiguities of his inherited terminology obscured many of his systematic achievements. Confusing distinctions and false controversies made things worse. As a result, his account of the notional acts has been poorly received, and its full implications have not yet been widely recognized. A better appreciation for this aspect of his thought would correct against perceived weaknesses of relation-centered accounts of the Trinity and open up new possibilities for contemporary trinitarian theology.