What are the differentiating characteristics of these persons thus constituted by relations of origin? Here Aquinas works out an impressive synthesis of the various biblical names given to the three persons such as Father, Son, Word, Image, Holy Spirit, Love, and Gift on the one hand and their ontological analyses and interpretations on the other. In the process he is also concerned to show how these names are thoroughly relational or personal and proper to each.
The Father
For Aquinas, the Father is not just one of the three persons but first and foremost the origin or “principle of the whole Godhead” (principium totius divinitatis) (Summa theologiae i, q. 39, a. 5). As such, the Father is the source of all things, both divine and created, without himself deriving from another, and in this sense the “unbegotten” “principle not from a principle” (principium non de principio), in contrast to the Son, who is referred to as the “principle from a principle” (i, q. 33, a. 4). In distinction from “cause,” which denotes diversity of substance and the dependence of one thing on another, Aquinas here prefers “principle” as more fitting to apply to God because this means only that from which something proceeds in any way whatsoever, that is, only a certain order of relation to each other (e.g., the point as the principle of a line), and origin without implying (temporal) priority, and is more comprehensive than “cause” (i, q. 33, a. 1).
For Aquinas, “Father” is the “proper” name of the person of the Father in the sense that it signifies paternity, which distinguishes the Father from the other persons and which is unique or proper to him. In fact, paternity, like generation, is predicated of God before creatures as regards its pure signified reality, although not as regards its finite mode of signification. In this regard, it is important to note that Aquinas does not locate the fatherhood of the Father in some moral qualities such as love and care independent of the act of generation, as do John D.
Zizioulas and Thomas F. Torrance, but precisely in the generation of the Son, as does the entire patristic tradition.2The essence of generation lies in the communication of the same nature to another, and the perfection of generation lies in the nearness and similitude of the generated to the
form of the generator. The Father’s generation of the Son is an infinitely perfect generation because the Father communicates to the Son the totality of his divine nature which is identical “numerically,” not just
“specifically” as in creatures, rendering the Father and the Son totally identical and equal in what they are, their essence as God, and mutually immanent, while distinguishing them only in their mutual relations as Father and Son. In this sense, paternity applies most properly, not metaphorically, to the Father, from whom all human fatherhood derives, as Ephesians 3:15 asserts (Summa theologiae i, q. 33, a. 2).
Fatherhood is not only the “proper” name of the Father but also his “personal” name in the sense that it defines his relation to the Son that constitutes the person of the Father, although it can also secon-darily be an “essential” name referring to the divine essence as such and applying to God’s relationship to his creatures. A name applies pri-marily to that which perfectly preserves the essential meaning (ratio) of the word and secondarily to that which does so in a partial way and in similarity to the former. Because of the oneness of the nature and glory that belong to the Father and the Son, the meaning of fatherhood is paradigmatically realized in the Father’s relation to the Son. Thus the name applies primarily to the personal relation between the two, and only secondarily to the relation between God and creatures where the two parties do not share the same nature, where creatures acquire a certain likeness to the creator only in proportion as they are “con-formed” to the Son by participating in his likeness to the Father. In this sense fatherhood is primarily a personal name defining the Father’s con-stitutive relation to the Son and only secondarily an essential name describing God’s relationship to his creatures (Summa theologiae i, q. 33, a. 3).
The Son
If the Father is above all the “unbegotten” origin of the divinity of the Son and the Holy Spirit, for Aquinas the Son is primarily the “begot-ten” of the Father born of the ineffable communication of the Father’s numerically identical divine nature and thus totally “consubstantial”
(homoousios) with the Father. The Son proceeds from the “substance”
of the Father, as creatures do not (Summa contra gentiles iv, 7, 5). This Son has two other names, Word and Image. Are these also personal and proper names of the second person, not essential names that apply to the divine essence as such? Do they both constitutively relate the Son to other persons (“personal”) and distinguish him from them (“proper”) as authentic trinitarianism would require?
For Aquinas, the Word in God, taken properly, is a personal, not essential, name. “Word” can mean three related things, the external sound, the concept of the intellect that constitutes the signification of the sound, and the external sound as imagined. Of these, of course, only the concept of the intellect can apply to the Word in God. “Word”
in the sense of the internal concept, however, refers to something that proceeds from something other than itself, that is, from the knowledge of the Father understanding himself, and contains in its very nature a reference to another from which it proceeds, that is, a relation of origin, which makes it personal, not essential. Just as Word in God is personal, not essential, so is speaking in God. There are not three speakers, the Father, Son, and Holy Spirit, as Anselm says. For Aquinas, as the Word is not common to the three persons, so speaking is not common to them either. To speak is to utter a word and implies a habitude or relation to the thing conceived and understood. As a relational name, speaking belongs only to the Father who utters the Word, and being spoken as a word is spoken belongs only to the Word. Insofar as being spoken also includes being understood in the word, it also belongs to each person to be spoken. As Aquinas succinctly puts it: “the Father, by understanding Himself, the Son, and the Holy Spirit, and all other things comprised in this knowledge, conceives the Word; so that thus the whole Trinity is spoken in the Word; and likewise also all creatures” (Summa theologiae i, q. 34, a. 1 ad 3).
Word is not only the personal but also the proper name of the Son. As an emanation of the intellect, Word is distinctive of the Son and belongs to him alone because the intellectual procession or emanation in God fulfills the meaning of generation in the most perfect way because of the numerical identity of the divine nature shared between the intellect and the intelligible in God, justifying and necessitating the name Son for the Word in which God’s self-understanding terminates. Word is the proper name of the Son as Son. In fact, Word is one of the many ways of expressing the perfections of the Son. In relation to the Father, the Son is called “the Son” to express his sharing of the same nature (connaturalis), “the Splendor” to show his co-eternity, “the Image” to manifest his total likeness (omnino similis), and “the Word” to express his being immaterially begotten. No one name can exhaustively express the richness of these divine truths.
The third name that Aquinas attributes to the Son is Image. Image is likewise both personal and proper to the Son. It is a personal name insofar as it implies origination or procession from something simi-lar to itself in nature or form. The Son is the perfect Image of the
Father because he receives the numerically identical divine nature of the Father, an imitation of the Father implying only assimiliation, not posteriority (Summa theologiae i, q. 35, a. 1). It is also a name proper to the Son, not to the Holy Spirit. It is true that both the Son and the Holy Spirit receive the nature of the Father through their respective processions. Still, the Holy Spirit is not said to be “born,” which makes it improper to call the Spirit the Image. The Son proceeds as Word, and it is essential to the Word to be of like nature or form with that from which it originates, but this is not the proper meaning of love, whose essence lies in the movement to the object loved, not similarity with it, although this similarity does obtain in the divine kind of love which is the Holy Spirit. Human beings are also called the image of God in the way that the image of a king may be found in something of a different nature like a coin, but the Son is the perfect Image of the Father in the way that the image of a king may be found in his son sharing the same nature (i, q. 35, a. 2).
The Holy Spirit
The third divine person, like the second, has three names, Holy Spirit, Love, and Gift, which are also both personal and proper names.
Unlike the procession of the Son, which has the name of generation, the procession of the Holy Spirit does not have an appropriate name, nor therefore do the relations that follow from this procession. “Holy Spirit”
does not seem of itself to indicate a relation like “Father” and “Son.” In order to meet this embarrassment, tradition has accommodated terms like “procession” and “spiration” to refer to relations, although they properly express originating acts more than relations. Nevertheless, Aquinas argues for the appropriateness of “Holy Spirit” in two ways.
First, it is appropriate for the Holy Spirit, who is common to the Father and the Son as their bond, to be called by a name that is also common to both. Both the Father and the Son are holy, and both are also spirits.
Second, “spirit” in corporeal things signifies impulse and movement, as in the case of breath and wind, and appropriately represents the prop-erty of love whereby love moves and impels the will of the lover toward the object loved, while “holy” refers to whatever is ordered to God. The Holy Spirit, therefore, is a proper name of the third person, who proceeds by way of the love whereby God is loved (Summa theologiae i, q. 36, a. 1).
Now, to touch upon an ecumenically sensitive issue, Aquinas argues that the Holy Spirit does also proceed from the Son, not only from the Father, that the Holy Spirit proceeds from the Father through the Son,
and that the Father and the Son are one principle of the Holy Spirit.
Aquinas makes a number of arguments for this thesis. First, the only distinction in God is due to relative opposition based on origin, as we saw earlier, which means that the Holy Spirit cannot be distinguished from the Son unless he is related and opposed to him either as that which proceeds to the principle from which it proceeds or as the prin-ciple to that which proceeds from that prinprin-ciple. Since we cannot say that the Son proceeds from the Holy Spirit, we must say that the Holy Spirit proceeds from the Son. Second, love must proceed from the Word because nothing can be loved unless it is first conceived and known.
Third, if two persons proceed from the one person of the Father, there must be some order or relation between the two, and this order within the same nature can be based only on origin. Fourth, the Father shares everything with the Son except what distinguishes each from the other, which means that one power belongs to both the Father and the Son, and whatever is from the Father must also be from the Son.
Insofar as the Son receives from the Father that the Holy Spirit pro-ceed from the Son, we can say that the Holy Spirit propro-ceeds from the Father through the Son, or immediately from the Father and mediately from the Son. This does not make the Son either a secondary source of the Holy Spirit independent of the Father, as J ¨urgen Moltmann might fear,3 or an instrumental cause of the Holy Spirit, because the power that the Son receives from the Father to spirate the Holy Spirit is not a numerically distinct but a numerically identical power. Because of the numerically identical divine nature totally shared between the Father and the Son, these are one in everything except where they are relation-ally opposed as Father and Son. Since there is no relative opposition in the matter of the spiration of the Holy Spirit, the Father and the Son constitute “one” principle of the Holy Spirit. Furthermore, the Father loves himself and the Son with one love, and the Father and the Son love each other, and it is from this mutual love that the Holy Spirit proceeds as their bond, as the “unitive love” (amor unitivus) of both (Summa theologiaei, q. 36, aa. 2–4; i, q. 37, a. 1 ad 3).
Can we predicate Love of the Holy Spirit? Can love be a personal name when it is also an essential name that applies to the divine essence as such and therefore to the whole Trinity? Is love not more a reference to an action than to a subsistent person? Here again we touch upon a certain linguistic peculiarity in naming the Holy Spirit. Just as “Father” can be taken both essentially and personally, so “Love,” if taken properly, can be taken both essentially as an attribute of the divine essence as such (Summa theologiae i, 20) and personally as the distinguishing attribute
of the Holy Spirit. For Aquinas, we are more familiar with the procession of the Word by way of the intellect than with the procession of Love by way of the will, and have been able to come up with more fitting names to describe the former than the latter. As a result, we are obliged to make do with circumlocutions such as “procession” and “spiration,” which are accommodated to refer to relations, although they refer to acts of origin in their proper meaning.
The Holy Spirit is not only Love but also Gift, which is a relational and therefore personal name. Gift implies an aptitude for being given and a relation to both the giver and the recipient to whom it is given. It is related to the giver, whose it is and who alone can give it to others, and to the recipient, who must be able to receive and possess it. The Holy Spirit and the Son belong to the Father by origin, who can therefore give them as gifts to others. Non-rational creatures, however, cannot truly receive and possess anything because they are not free to use and enjoy what they possess; they can be moved by a divine person but not enjoy him. As creatures capable of freely knowing and loving, rational creatures meet the necessary condition for receiving and possessing the divine gifts, but not the sufficient condition. Receiving, enjoying, and partaking of the divine Word and the divine Love so as to freely know and love God truly and rightly is not within their own natural power.
The power to do so must come from above, that is, must be given to them by God and thus as a gift. A divine person can be given and be a gift only by divine grace. The Holy Spirit is given to creatures only in time, but the aptitude to be given is eternal. The Holy Spirit is Gift from all eternity (Summa theologiae i, q. 38, a. 1).
Gift is not only a personal name but also a proper name of the Holy Spirit. A gift in the proper sense is something gratuitously given without the expectation of a return. The reason for gratuitous donation is love whereby we wish the recipient well. All true gifts are possible only through love, which therefore constitutes the first or primordial gift as condition of all genuine giving. Since the Holy Spirit proceeds as Love, he is also the first gift. The Son too is given, but given precisely from the Father’s love. Gift, therefore, is also the proper name of the Holy Spirit, as is Love (Summa theologiae i, q. 38, a. 2).
Mutual equality and indwelling
The same divine nature subsists in the three persons, making them alike, and does so in indivisible, perfect equality. We cannot say that the divine essence belongs more to the Father than to the Son. We can say, therefore, not only against Eunomius, that the Son is like to the
Father, but also, against Arius, that he is equal to the Father. By the same token, two divine persons do not mean more than one person, although two human persons mean more than one person. All the rela-tions and persons are numerically one in essence and being. In a most profound statement of the trinitarian mystery of infinite sharing among the persons, Aquinas says that “all the relations together are not greater than only one; nor are all the persons something greater than only one;
because the whole perfection of the divine nature [tota perfectio divinae naturae] exists in each person” (Summa theologiae i, q. 42, a. 4 ad 3).
Contemporary trinitarian theology is fond of the idea of perich ¯or ¯esis or the co-inherence of the divine persons in one another as an indication of the interpersonal communion that constitutes the life of the Triune God. The Father is in the Son, and the Son is in the Father (Jn 14:10).
What is the basis of this co-inherence? Aquinas gives three reasons based on essence, relation, and origin. First, the Father exists in the Son by his essence insofar as the Father is his essence and generates the Son by communicating that essence in its totality. The Father’s essence, that is, the Father himself, exists in the Son, who too is his own essence and is in the Father in whom he has his essence. Second, relations constitute the persons, who are subsisting relations to one another. The Father exists in the Son and the Son exists in the Father as mutually constituting opposites. Third, the procession of the intellectual word, as an immanent activity, occurs within, not outside, the speaker of the word. The same applies to the Holy Spirit (Summa theologiae i, q. 42, a. 5).