In light of recent discussion (between those within the Council and its friends) on the doctrine of the Eternal Generation of the Son, here are Richard Muller’s relatively brief statements (from his theological dictionary) on the doctrine of the Trinity, which touch upon the issues that are part of the discussion (for more see here):

 

Trinitas: Trinity; viz., the existence of God as one in essence (essentia, q.v.) and three in person (persona, q.v.). The doctrine of the Trinity arises out of the church’s reflection on the biblical declaration that God is one but is known as Father, Son, and Spirit. The correlation of the way in which God is known through his self-revelation and the way in which God truly is in himself constitutes the necessary presupposition of true doctrine, i.e., of the truth of the revelation itself; therefore the revelation that God is one and the revelation that God is three cannot be reduced to an eternal oneness and a temporal or economical threeness. Equally, the oneness cannot be defined in such a way that it ultimately abolishes the threeness, or the threeness in such a way that it ultimately abolishes the oneness. Trinity, therefore, is an attempt to avoid both a monadic oneness and a tritheistic view of God through the affirmation that God is one in essence and three in person. The terms used to elucidate this doctrine come from both the patristic and the medieval church. For convenience, we introduce the patristic terms first and then give their later scholastic equivalents and elaborations. (NB: Important terms employed in the following section are defined individually, some at length, elsewhere in this dictionary.)

The first important set of terms was established by Tertullian (ca. 220) in his debate with the modalistic monarchian heresy. Against the notion that the monarchy, or sole rule, of God could best be explained if the Father, Son, and Spirit were modes or roles taken by the one God in his self-revelation, Tertullian argued for the eternal truth of God’s existence as one and as Father, Son, and Spirit: God is one in substantia (q.v.), or substance, and three in persona (person). In the Greek church, the problem was not so much establishing a language of oneness and threeness as it was defending the essential oneness or numerical unity of the Godhead in the Father, Son, and Spirit. Against the subordinationistic and tritheistic view of Arius, Athanasius and the Council of Nicaea (325) argued for the consubstantiality of the Father, Son, and Spirit. The Arians viewed the persons as of different essence (heteroousios) and as unlike (anomoios); Athanasius held that the persons were of one essence, or consubstantial (homoousios). Although the term homoousios was embodied in the Creed of Nicaea, many bishops of the fourth century doubted the wisdom of speaking about God in the potentially materialistic philosophical language of essence (ousia). Others, accepting the language of ousia, thought that homoousios, or consubstantiality, threatened the conception of God as truly three. They found the term reminiscent of modalistic monarchianism. So they proposed to argue, against both the Arians and the Athanasians, that Father, Son, and Spirit were of like essence (homoiousios) or, with a view to avoiding the question of essence entirely, that Father, Son, and Spirit were like or similar (homoios). Final acceptance of the Athanasian language of homoousios was made possible by the use of that term in connection with an adequate explanation of the threeness of the Godhead. This was the achievement of the Cappadocian fathers: Basil of Caesarea, Gregory of Nyssa, and Gregory of Nazianzus. The Cappadocians argued for one ousia but three hypostases, defining hypostasis as a particularization, or an individual instance, of an essence, or ousia. Thus Peter, James, and John are three individual instances, or hypostases, of the essence, or ousia, of humanity. In order to avoid a tritheism of three essentially coequal gods, the Cappadocians further stipulated that the entire divine ousia is indivisibly present in the three hypostases or, more precisely, that the three hypostases are eternally subsistent relations in the one ousia. Expressed individually as relations, the hypostases of the Father (Pater), Son (Huios), and Spirit (Pneuma) are the unbegottenness (agennēsia) of the Father, the begottenness (gennēsia) of the Son, and the procession (ekporeusis) of the Spirit, all of which occur eternally, without beginning or end, in the divine ousia. This trinitarian model is characterized by a unity of essence and a threeness, with relational subordination in order only. The Father is understood as the first principle (archē) of the Trinity and therefore as the unifying principle of the hypostases. The Son is begotten from the Father, and the Spirit proceeds from the Father through the Son.

 

The Western, or Latin, fathers recognized the validity or orthodoxy of this Greek expression but realized also the difference between it and the Western view, together with the difficulty of establishing Latin equivalents to the Greek terms used by the Cappadocians. Ousia, expressive of the oneness of divine essence, was viewed as the equivalent of Tertullian’s substantia, substance. Hypostasis, however, was only with difficulty assimilated to persona, since before the Cappadocian modification of the term, it had been used synonymously with ousia and also translated as substantia. In addition, persona, or person, does not have a philosophical or metaphysical capability coordinate with that of substantia. Two terms were therefore ultimately added to the Latin vocabulary, both of which had a major impact on scholastic formulation: subsistentia, indicating an individual instance of a substantia, as the equivalent of hypostasis; and modus subsistendi, mode of subsisting or manner of subsistence, as an attempt to express the implication of hypostasis as a relation within the Trinity. The latter term is particularly important for the distinctive Western and Augustinian view of the coequality of the persons as modes of subsistence of the one divine substance or essence (essentia). In the Western view, order and relation do not indicate subordination but are rather evidences of absolute coequality. Rather than view the Father as alone proceeding the Spirit, Western trinitarian theory argues for the double procession of the Spirit from the Father and the Son (filioque, literally, “and the Son”) and views the Spirit as the bond of love (vinculum caritatis, q.v.) between the Father and the Son. In this view the Spirit stands as a reciprocal relation between the Father and the Son; here, in contrast to the Greek theory, the Spirit accounts for the oneness of the three persons. In both the Greek and Latin trinitarian theories, the common possession of the entire essence by the persons is described as a coinherence of the persons in the essence and in one another: perichōrēsis (q.v.) or emperichōrēsis (q.v.) in Greek, circumincessio (q.v.) in Latin. Although it became the normative Latin usage to replace substantia with essentia, homoousios was rendered by both coessentialis and consubstantialis, coessential and consubstantial. Trinity can thus be defined as three persons in one divine essence (tres personae in una essentia divina) or as one divine essence subsisting in three modes (una divina essentia in tribus modis subsistis), the unity of essence being guaranteed by the consubstantiality and coinherence of the persons, the distinction of persons being manifest in their relations.

 

This patristic terminology was drawn into the scholastic formulation of the doctrine, with Latin equivalents being established for all the Greek terms and with general categories being developed in order to understand or describe the relation of the terms one to another. All the relations of the persons and corresponding activities or operations in the divine essence are called by the scholastics operationes or opera Dei personalia, operations or personal works of God. The term serves to distinguish the begetting and the proceeding of Son and Spirit from the common work of the Godhead, the opera Dei essentialia, or essential works of God. The opera Dei personalia can be considered (1) in terms of the activity itself of begetting and proceeding, (2) in terms of the persons or hypostases themselves, (3) in terms of the relations between the hypostases, and (4) in terms of the full set of personal characteristics implied by the persons and their relations.

 

Thus (1) the Trinity is seen in terms of two emanations (emanationes): the begetting (generatio), or generation, of the Son; and the procession (processio), or spiration (spiratio), of the Spirit. Generatio is the Latin equivalent of gennēsia, and processio that of ekporeusis. (2) The two emanationes imply the three personae, or hypostases, of the Trinity: the Father (Pater), who begets the Son and spirates the Spirit; the Son (Filius), who is begotten by the Father and who also spirates the Spirit; and the Spirit, who is spirated by or proceeds from the Father and the Son. Note that the scholastics assume the Western trinitarian model and the filioque or double-procession of the Spirit. (3) The two emanations and three persons are related to one another in this model by four personal relations (sg., relatio personalis): the Father relates to the Son by his active generation (generatio activa) of the Son, and to the Spirit by his active spiration (spiratio activa) of the Spirit; the Son relates to the Father by his begottenness or passive generation (generatio passiva), which is also termed filiation (filiatio), and to the Spirit by his active spiration of the Spirit, identical with the spiratio activa of the Spirit by the Father; and the Spirit relates to the Father and the Son by his procession, or passive spiration (spiratio passiva), from both Father and Son. The four personal relations, therefore, are generatio activa, generatio passiva, spiratio activa, and spiratio passiva, each active emanation being reflected in a passive reciprocal relation. (4) The trinitarian language is completed by the delineation actively and passively of the hypostatic or personal character (character hypostaticus sive personales) of each of the three persons, or in other words, by the statement of the five notiones personales that identify the three persons individually and in their relations. The hypostatic character of the Father is his paternity (paternitas), which is defined by three notiones, or notions: innascibilitas, or unbegottenness, generatio activa, and spiratio activa. (Innascibilitas is the Latin equivalent of agennēsia.) The hypostatic character of the Son, loosely called filiatio, is defined by two notiones: generatio passiva or filiatio, strictly so called, and spiratio activa. The hypostatic character of the Spirit, loosely called processio, is defined by one notio, or notion: spiratio passiva. The personal notions or characteristics (notiones personales) are thus identical with the relationes personales, with the addition of the unbegottenness, or innascibilitas, of the Father.

In describing the common work of the Godhead, scholastics observe the pattern of relations and notions by declaring that the Father, who is from none (a nemine), is the source of trinitarian activity (fons actionis; see fons); that the Son, who is from the Father (a Patre), is the mediating agent or means of action (medium actionis); and that the Spirit, who proceeds from both (ab utroque), is the limit of the activity or operation of the Godhead (terminus actionis). This pattern of operation is observed in all the essential works of the Godhead (opera Dei essentialia), with the sole exception of the incarnation (incarnatio), in which the Son is, as the Incarnate One, the terminus actionis. Since all three persons of the Trinity participate in this essential work, it is also called the common work (opera communia) of the Godhead and is described by the maxim Opera Trinitatis ad extra sunt indivisa (q.v.), The externally directed works of the Trinity are undivided. See vestigia Trinitatis.

 

Muller, Richard A.. Dictionary of Latin and Greek Theological Terms: Drawn Principally from Protestant Scholastic Theology (pp. 369-373). Baker Publishing Group. Kindle Edition.