Divine Simplicity

Thomas Joseph White O.P.

The conceptual notion of divine simplicity is a contested one, both in modern continental Christian theology and contemporary analytic philosophy. Nevertheless, it is of central importance in the patristic and scholastic traditions of mainstream Christian theology and has a place in significant conciliar decrees. This article suggests that the notion has an implicit foundation in key biblical teachings regarding the oneness and uniqueness of God the Creator, as well as in the notion of the Trinity, since the three persons in God are affirmed to be one in being and nature, wholly unlike three individual human persons. Having noted key patristic and medieval definitions of divine simplicity, the key teachings of Thomas Aquinas on the topic will be summarized. Other medieval perspectives on simplicity are considered, as well as some modern philosophical challenges to the doctrine. Then the contours of the theological treatment of divine simplicity in the modern period will be explored, noting the teaching of the First Vatican Council, the modern continental trinitarian tradition, and modern analytic criticisms, respectively. It will be argued that in each of these instances, classical treatments of divine simplicity from the patristic and scholastic periods are of perduring importance in maintaining a conceptually balanced, historically responsible, and theologically plenary expression of orthodox thought in regard to the mystery of God the Holy Trinity.

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EssenceTrinitarian theologyScholasticismPatristic theologyDivine compositionExistenceCreationMutual indwellingDivine corporeality

1 Introducing divine simplicity

The topic of divine simplicity encompasses several central questions. For example, is God’s essence ontologically composite and if so, in what way? Or, if God’s essence is not ontologically composite, how does God differ from creatures? Does God have a physically composite body, or distinct spiritual faculties, such as an intellect distinct from his will? Are his attributes (such as power, wisdom, and goodness) formally distinct or really identical? Does God receive his existence from another or from himself, similarly to creatures? Does God have accidental properties that characterize him, such that he is subject to historical change in non-essential ways? Answers to such questions have obvious implications for any Christian doctrine of the Trinity, since they directly affect how one understands both the distinction and unity of the trinitarian persons. Are the persons of the Trinity distinguished by being different persons of the same essential kind who are not identical in individual being (like three human persons), or are they identical in individual being and essence, and thus non-composite in a way that is utterly distinct from human persons? Do they have distinct accidental properties while sharing in one divine essence and individual being, so that each person can develop natural properties as God that the other two persons do not have? Or are their qualities (like power, wisdom, and goodness) really identical with their essence, so that they are really distinct only in virtue of their intra-trinitarian relations of origin, even while being one as God?

Such questions have a medieval scholastic feel to them, but as we shall see below, they also have roots in biblical notions about God from the Old and New Testaments, especially as the Bible was interpreted in the patristic era, in which manifold reflections about divine simplicity arose, especially in the context of trinitarian theology.

In modern continental trinitarian theology, the topic of divine simplicity is largely either ignored or thoroughly reconceptualized. There are several reasons for this. First, a common strand of modern theology (represented by figures like Albrecht Ritschl and Adolf von Harnack) considers classical divine attributes (such as simplicity and impassibility) to originate primarily from Hellenistic metaphysical speculation alien to the Judaic and biblical world of thought, and thus extrinsic to the enlightened prerogatives of a modern, historically informed theology. Second, major figures of the ‘trinitarian renewal’ of the twentieth century, such as Karl Barth, Sergius Bulgakov, Karl Rahner, and Hans Urs von Balthasar, provide no thematic treatment of divine simplicity, despite its presence in patristic theology and in various conciliar definitions. This silence stems not from ignorance but from a selective decision to relinquish the use of some (but not all) classical metaphysical themes, in light of the just mentioned genealogical claim. They each seek in various ways to respond to challenges to divine simplicity enunciated by modern secular philosophers with innovative theological proposals that do not rely on seemingly questionable pre-modern philosophical ideas about the divine essence. This modern strategic rethinking of trinitarian theology is coupled with the decision to appropriate apologetically some categories of post-Hegelian philosophical ontology that depict God in event-orientated, historical terms. Thus, such modern trinitarian theologies typically depict God, his deity, and the trinitarian persons in great part in relation to the economy of creation and salvation, and therefore in dynamic terms not fully compatible with the classical ideas pertaining to notions of trinitarian simplicity and immutability. Finally, some analytic theists, while open to a host of classical questions, consider the doctrine of divine simplicity unsustainable, since they believe that it entails either that God’s attributes (such as goodness or eternity) be considered in a reified way as identical with his essence, and thus God is transformed into an abstract entity, or they fear that a God who is simple can neither know, love, nor respond dynamically to the real world of change, freedom, and history that characterizes creation, and human beings especially.

This article seeks to show that the neglect of divine simplicity by modern theology is unjustified, since the doctrine of simplicity is arguably of biblical provenance and is essential in patristic and medieval theology to a coherent account of the intra-trinitarian life of God. Classically, the doctrine serves as a logical condition of possibility for a coherent idea of the Trinity as Creator, who can know and love the world in the most perfect of ways precisely in virtue of God’s transcendent divine simplicity. In light of these considerations, this article suggests that the doctrine of divine simplicity can and should be considered a constitutive element in any comprehensive theological treatment of the Christian doctrine of God.

2 Biblical topics that point toward the implicit scriptural origins

The notion of God’s simplicity as a first principle of reality, is first discussed explicitly not in the Bible but in Graeco-Roman philosophical literature, including in the work of Aristotle (Metaphysics: 12.7.1072a 32–34 [see 1995]) and Plotinus (Enneads: 1.6.1, 5.4.1, 5.9.3, 5.9.14 [see 2019]). By contrast the notion of divine simplicity is not mentioned explicitly in either the canon of the Old or New Testament. In his discussions of divine simplicity, Aristotle is concerned to show that the first principle in all of reality is purely actual, not characterized by material potency, and that God’s eternal intellectual life is non-compositional, distinct from the kind of historically developmental, abstract, and rationally discursive knowledge that characterizes human beings. Plotinus is concerned, similarly, with the maximal perfection of the One, the first principle of all things that are found in the world, upon which all others depend, insofar as they are derived from what is primary. For Plotinus, causal derivation implies ontological composition, while primacy implies simplicity.

Notions such as these originating from Hellenistic philosophers were taken up and employed in selective ways by Christian patristic and medieval authors. However, it is problematic to presume for this reason that early Christian theological notions of divine simplicity are primarily of Hellenistic origin or are specifically philosophical in content. One may argue, as patristic and medieval authors did themselves, that their theological treatment of the topic derives principally from notions of God conveyed within biblical literature. Here this article proceeds not chronologically but thematically and will mention briefly five biblical notions that implicitly require recourse to topics involving divine simplicity.

First, there is the question of the individual unity or multiplicity of deities in Old Testament literature. Clearly the proponents of mature Judaism, exemplified in the post-exilic Second Temple period, posited the reality of one God alone, as the true and unique God (Bauckham 2008). They came to do so against the backdrop of various competing forms of religiosity – such as Near Middle Eastern or Graeco-Roman – some of which envisaged divinity in pluralistic form, in pantheons or by means of polytheism. For Old Testament authors to depict God as one and unique, they needed implicit recourse to the notion of God’s nature, or deity, as instantiated only in God individually. While there are many humans and many angels, there is only one Lord of Israel (Deut 6:4). There is only one God, the Creator (Exod 3:14–15; Isa 45:5–13; Ps 102:24–25). This is a classical way of thinking precisely of divine simplicity.

Second, the question arises in the analysis of Old Testament literature of whether the ancient Hebrews or some of their members envisaged their deity under corporeal terms. Visions of Yhwh that suggest corporeality (Exod 24:9–11; Ezek 1:4–28), may well be read metaphorically or be interpreted as anthropomorphic visions of God accommodated to human understanding. However, some scholars have proposed that at least some strands of Old Testament literature indicate belief in a localized, corporeal deity (Barr 1959: 31–38; Smith 2016). My aim here is not to offer justification to such views, but only to note that such historical questions inevitably touch upon the topic of God’s composition as a being, and thus affect our judgments about the simplicity of the divine nature. Did some ancient Hebrews believe that Yhwh had a physical body and in this case is God an ontological composite of natural form and bodily matter? By contrast if one can plausibly read such texts as metaphorical, does this mean the divine nature is non-composite in the senses previously indicated (non-material) and thus simple, when contrasted with physical bodies?

Third, there is the question of Yhwh’s relationship with the angels in Old Testament literature and the development of the angelology of later Judaism (Bonino 2016a). Some scholars claim that in some texts ‘the Lord, Yhwh’ may be read as one or merely the first among the ‘sons of God’, where the latter phrase may indicate either angelic beings or a consortium of deities (Smith 2003). Others read passages of these kinds as indicating by ancient metaphorical discourse the uniqueness and superiority of the Lord of Israel among all the other supposed Gods or among all the angels who the nations take to be gods (Miller 2000). In either case, the interpretation of biblical texts rests upon implicit notions of individual uniqueness of Yhwh, the Lord, as one who has a nature distinct from and transcendent of the angelic host and the supposed gods worshipped problematically by non-Israelite peoples.

Fourth, there is the theme of the God of Israel as the unique creator of all that exists in creation, evidenced in Second Isaiah (45:14–25), and in the final redaction of Genesis 1–2, as well as in the scribal literature of the Second Temple period (Brueggemann 2012: 145–151; Sir 16:26–30; Wis 7:22–30). God alone creates and gives being to all that is, to all that is not God. In this case, existence or being pertains to created things in a way that is different than the way it pertains to God, who simply exists eternally, while other things come into being, due to the initiative and sustaining activity of the Creator. In short, at least some biblical texts affirm that the world is created by the one God of Israel (Ps 96:5; Ps 148:2–5; Jer 10:12–13; Isa 66:2; Neh 9:6; Prov 3:19; Job 33:4). In this case, God’s being is not causally dependent, in the way that the being of creatures is. Therefore, God does not exist in the way created realities exist and his being is not composite as theirs is, by subjection to a ‘complex composition’ of potential and actual existence, such that they have they potency to be or not be. God simply is.

Finally, we can indicate a theme that is proper to the New Testament, and that has to do with the implicit but clear denotation (at least in some books of the New Testament) that both Jesus and the Spirit are divine and one with God, the Father of Jesus Christ (Phil 2:6–11; Gal 4:6; Rom 8:9–10; John 1:1–3; John 16:13). If there is a real distinction of persons in God – that is, the Father is eternally distinct from his Son and Word, who are in turn distinct from the Holy Spirit (or Paraclete) – and yet God is also one, one is led to question precisely how these two assertions can coincide. Orthodox Christianity of the fourth century employed the homoousios (literally: of the same substance or essence) formula at Nicaea to convey the unity of essence (or consubstantiality) common to the persons, indicated as truly distinct hypostatic subjects. However, it follows from such a formulation (which has a basis in the teaching of the New Testament regarding the divinity of Christ and the Spirit) that the Trinity is ontologically simple in a way three human persons are not, since three human beings may have one nature or kind but are three individual substances, whereas the three persons of the Trinity are one in being and substance and not merely one in natural kind. Here the divine simplicity pertains essentially and inalienably to a coherent doctrine of the Holy Trinity as such.

3 Patristic expositions

3.1 Irenaeus

Patristic reflections on divine simplicity are numerous. Here this article considers three particularly noteworthy cases that build by logical congruity on the notions enunciated above. The first pertains to the work of Irenaeus. In Against Heresies (2.13.8 [book II]; see 2004), Irenaeus famously engages critically with Valentinus’ theology of the divine pleroma (plenitude of divine being), which he analyses based upon his reading of the Gospel of Valentinus. In doing so he notes a fundamental incongruity in the thought of the Gnostic author. On the one hand Valentinus espouses a doctrine in which the material world is ontologically deficient or evil, derived from a pre-cosmic, primal fall in the pleroma. The deity split by inward schism, gives rise to the material world. On the other hand, Valentinus also considers the membership in that pleroma to be pluralistic and multiple, in a way that is most readily conceivable and imaginable in material terms, so that one element of the deity (Sophia) can break corporate communion with others. Irenaeus notes that God is the creator and author of complex material realities, which are good in themselves, but that in contrast to them, he is not composite in a material way. The three agents of salvation – the Father, his Word, and his Spirit – are one and are spiritual, or immaterial, not physical and composite. Therefore their ‘plurality’ or distinctiveness does not imply composition and multiplicity of the kind found in created material realities (Barnes 2009: 67–106). The God of the Old Testament is God the Creator and is also God the Father, Son, and Holy Spirit. This God is one and is without material parts.

3.2 Cappadocians

A more developed teaching on divine simplicity in the Holy Trinity emerges in the thought of the Cappadocian fathers, Basil the Great, Gregory of Nazianzus, and Gregory of Nyssa. The Cappadocians were confronted with the objections of Eumonius and other fourth-century Anomoeans who denied the divinity of the Son and the Spirit. Eunomius argued that the Father alone was God and that his essence was characterized by unbegottenness, such that anything begotten was not of the essence of God (Ayres 2004: 144–149; Gregory of Nazianzus, Oration 29: no. 11 [see 1994a]). Therefore, the begotten Son is not truly one in essence with the Father (as Nicaea had asserted). To counter this idea, these fathers developed the notion of relational identity in the trinitarian persons, whereby the Son and the Spirit are distinguished from the Father because they derive from him by way of relations of origin (in eternal begetting and spiration respectively). However, the Son and the Spirit receive from the Father all that pertains to the essence of the divine nature such that they are truly equal and identical to him in being (Gregory of Nazianzus, Oration 31: no. 9 [see 1994b]). In this respect the Trinity is simple (non-composite) because the Son and the Spirit as hypostatic persons are identical in being and essence with the Father, not inferior or alien in any respect (Gregory of Nyssa, Against Eunomius: 1.19, 1.22 [see 2004a]; Gregory of Nyssa, Not Three Gods[see 2004b]). As a culturally proximate influence, Plotinus (Enneads: 5.4.1, 6.9.4) had argued for the simplicity of the first principle in the deity, the One, from whom Nous and Psyche derive, and who are ontologically subordinate to the One. The simplicity of the One implies the subordination and inequality of the Nous and Psyche. But in the Cappadocian affirmation of divine simplicity the notion is affirmed precisely to alleviate or render impossible any inequality of the persons, therefore underscoring their real identity as each being the one God. Consequently, their view is non-hierarchical and is monotheistic, in a decidedly trinitarian-biblical way, that contrasts markedly with a prominent strand of non-biblical Hellenistic philosophy of the time. The doctrine of divine simplicity as it emerges in the Cappadocians, then, is distinctly Christian and theological in character.

3.3 Augustine

A final example, and the one that is historically of greatest influence in Western theology, pertains to the work of Augustine of Hippo. In the fifth book of his work The Trinity (5.1.6), Augustine is concerned to respond to Arian criticisms of trinitarian faith, most notably to the idea that the Son and Spirit must be inferior to the Father. There he posits that the Son and Spirit are identical with the Father in essence, and are wholly and truly God. They are distinguished from the Father only by relations of origin, not properties pertaining to the divine nature (Augustine, The Trinity: 5.1.6). However, Augustine continues in this argument to specify that properties of the divine nature (wisdom, goodness, etc.) are not merely accidents or potential properties of the substance of the godhead but are somehow mysteriously identical with the godhead. God does not merely have wisdom or goodness but is subsistent wisdom and goodness. This subsistent wisdom and goodness are proper to all three persons, so that the Father does not become wise by generating the Son, or good and loving by spirating the Spirit. Rather, the Father communicates all that he subsists in as God, in his eternal wisdom and goodness, to the Son and to the Spirit, by generation and spiration respectively. Here one can mark a new development in the patristic reflection on divine simplicity that posits a non-composition of substance and property in God’s essence. Augustine invokes this negation of composition to underscore the distinctive unity and identity of being present in the three persons who are the one God. The three persons are not distinguished by any individual properties or accidents pertaining to the divine nature, but each possess that nature in its fullness and singularity of being. They are each the one God.

4 Medieval theologians

4.1 Doctrinal background to medieval theories of divine simplicity

Medieval Christian theological reflections on divine simplicity are manifold, and in fact extremely diverse. The treatment of the topic by various well-known theologians is far from homogeneous. On the contrary, it is often indicative of ideas proper to a given thinker. However, parameters of unity were provided by several factors. One of these was the thought of Augustine on divine simplicity, which acted as a proximate inspiration for most Western theologians. Likewise, there were two important public debates in the twelfth century regarding trinitarian theology that led to ecclesiastical formulations of a doctrine of divine simplicity. The first of these had to do with the claims of Gilbert of Poitiers (d. 1154), which were rejected by the Council of Reims in 1148. Gilbert noted that the essence of the three persons in God must be one and the same, since they are each the one God. He concluded from this, however, that the relations of origin between the persons must be something distinct from their essence, since the essence unites them, but the relations distinguish them. He concluded that there must be a distinction between each of the persons and their relative properties, since each person is essentially God and is related to others only accidentally (Expositio in Boecii de Trinitate 1.5, nos. 42–42; in Gilbert of Poitiers 1966: 148; Emery 2007: 90–91). According to this view, relations are accidental to the substance of a trinitarian person, much as they would be in human persons. God the Father is not identical with his paternity or his relation to his Son. Rather, he merely possesses paternity, while sharing the essence of God with the Son. In this way of thinking, the three persons of the Trinity are conceived of as relatively similar to three human beings identical in essence (as human), and related merely by accidents or properties (as in a father and son relation, for example). This position was criticized by Bernard of Clairvaux and condemned by the Council of Reims because it failed to acknowledge the simplicity of the divine nature of the Trinity, along the lines indicated by Augustine (Evans 2000: 75–77, 123–127). On Augustine’s view the relations of the persons are not accidental additions to a substance, but pertain in some mysterious way to the very substance of the divine persons.

This Augustinian medieval idea of the Trinity is apophatic in many respects, since it implies that the divine communion of persons in God is utterly dissimilar to the relations of human persons. However, it does also suggest that we can think of the persons in the Trinity by analogy with created persons, if we take divine simplicity (and thus divine transcendence) into account. Such an idea was developed more expressly at the Fourth Lateran Council in 1215 which took issue with the theology of Joachim of Fiore (d. 1202). Joachim had written against Peter Lombard who had affirmed in his writings that one may not say that the essence of God begets or spirates. By error, Joachim believed that this claim implied that Lombard was treating the essence in God as a kind of additional fourth subject, really distinct from the three persons who are subject to begetting and spiration. He responded by affirming that the essence of God begets and spirates, and in doing so, attributed processional activities to the essence of God. On this view the persons seem to each have distinct essential attributes that differentiate them, such as natural begetting or natural being begotten. Therefore, they seem to have essential differences (that is to say differences of essence), and so to be united as one only morally or ethically as in a communion of human persons, who are not truly consubstantial. Joachim may have wished to indicate that the eternal processions of the trinitarian persons just are what God is (the processional life of Father, Son, and Spirit). However, in the process, he affirmed that the essence itself differentiates in composite ways, due to the divine processions. The Fourth Lateran Council rejected this view by explicitly appealing to the simplicity of the divine nature (Tanner 1990: 232 [vol. 1]). The Trinity is more dissimilar than similar to a communion of created persons. The Father, Son, and Holy Spirit are distinguished only by relations of origin, but these are not properties or accidents. The whole substance of the godhead is communicated from the Father to the Son by eternal generation and from the Father and the Son to the Holy Spirit by eternal spiration. Each person thus possesses the fullness of the deity in its perfection and simplicity, and each person is truly the one God.

Theologians in the medieval Catholic Church saw rightly that both of the problematic positions noted above fail to understand sufficiently the implications of the doctrine of divine simplicity. If the nature of God is simple, then there cannot be personal relations in God that are extrinsic to his essence. Nor can God’s nature be subject to diverse composite activities of self-differentiation, like begetting and spirating. The three persons are distinct, but they are only truly one in essence because each person of the Holy Trinity partakes fully of the one divine nature of God.

4.2 Thomas Aquinas on divine simplicity

Aquinas treats the doctrine of divine simplicity in multiple places in his corpus, but this article concentrates on his mature positions presented in the Summa Theologiae (ST), especially ST: q. 3 (part I), as well as in the treatment of trinitarian relations and persons in qq. 28–29, which, it shall be argued, is a logically related topic. In ST: q. 3 (part I), Aquinas discusses various forms of ontological composition that pertain to creatures, or logical complexity that pertains to our way of thinking conceptually about creatures, and he systematically denies that such forms of composition pertain to the divine nature. He thus denies that our logical conceptions of composition can be rightly ascribed in a literal way to God. It is important to note that in this context (ST: q. 3 [part I]) Aquinas is reflecting on the mystery of the divine essence, which Christian theology claims is proper to all three trinitarian persons (homoousios). Therefore, his reflections on divine simplicity are organically related to a broader vision of trinitarian theology that is being explored. Here four of the principal forms of composition in creatures and non-composition in God that Aquinas treats will be noted, all of which have some foundation in the biblical and patristic material noted above, and all of which have consequences for Aquinas’ understanding of the Trinity.

4.2.1 Form and matter

Following Aristotle, Aquinas thinks that every physical, material being that humans experience in the cosmos is a form-matter composite (Aquinas, Opusculum De Principiis Naturae: cc. 3–8 [see 1954]). ‘Form’ in this context designates the substantial determination of a given thing such that it has a nature of a given kind and properties that are specific to that nature. The form of an orange tree, for example, is its genus and species. Each tree falls within the genus of vegetative living things, and additionally within the species of trees that produce a distinctive kind of fruit, according to its organic constitution and material properties. Understood in this way, the form of a physical reality accounts for its nature, properties, and sameness of kind, relative to others. Matter, meanwhile, denotes the physical component parts of a natural form, as well as the radical potency present in and through all the material parts, such that every physical reality is potentially subject to indefinite transformation, by substantial corruption and the subsequent generation of new forms. Even though it is always subject to potential transformation, the matter of any given reality is also always actuated by the natural form such that all the material parts are organized and arranged as parts of a given kind of thing, and they express the nature and properties of that form, in and through their material configurations. The material body of a hound is different from the material body of a human being, a fir tree, or a lake.

In virtue of these two principles, which are always present and mutually implicated in all material bodies, every physical reality we come to know is ontologically composite. Why then would we not ascribe a similar kind of ontological composition to God? Aquinas gives several reasons (ST: q. 3, a. 2 [part I]). One is that any material thing is inevitably subject to passive change due to the action upon it by other realities, and therefore is a reality caused by and ontologically dependent upon other realities. However, God the Creator is, by biblical definition, the one who gives being to all created realities. It is he who causes them to be, and not the inverse. Consequently, the divine nature cannot be a material thing, one that depends for its being on others. Likewise, Aquinas thinks that God is pure actuality, a plenitude of being that is transcendent and incomprehensibly perfect, and that gives being to all others, so his being is not subject to the potentiality of becoming more perfect. If he were material this would be the case, as he would be continually subject to the potency of alteration for an ameliorated state. Thus, the divine nature is not a material body.

Arguments of this kind lead Aquinas to affirm that God is simple in a way material beings are not, since he is not a composite of form and matter. We should note the principally apophatic character of this affirmation. God’s nature cannot be imagined, represented sensibly, or conceived of after the fashion of any of the material bodies that we continually experience. He is the author of the physical cosmos and is even intimately present to all he creates as its transcendent author, but he is not a material being and in this sense is unimaginable.

Evidently this understanding of God aligns closely with the biblical and patristic notion we explored above, that God is not a material body. The idea also has trinitarian consequences. If the nature of God common to all three persons is not material, then the distinction of persons in God cannot take place in virtue of a material distinction of the divine nature, as if one person were to have some composite part of the deity and another person were to have another part. Instead, one must find alternative analogies to conceive of the distinction of persons in God, based on immaterial procession, so as to think about the eternal generation of the Word and the eternal spiration of the Holy Spirit. Classically this is done by appeal to the analogy from human acts of the mind, that is to say, by conceiving of the Son analogically as the Logos or immaterial Word of the Father, who proceeds from the Father by similitude to a human act of immaterial understanding, and by conceiving of the Spirit analogically as Love, who proceeds from the Father and the Son by similitude to a human act of immaterial willing or of love (ST: q. 27 [part I]).

4.2.2 Essence and individual

The second negation of composition in God follows closely from the first. Every material thing we encounter is an individual of a given kind. A given human being, such as St. Paul, is not identical with human nature as such, but is one individual having human nature. The world we experience consists of a variety of such kinds of beings, such as humans, horses, trees, and so forth, each of which kind is instantiated not in a platonic idea, but only ever in a multiplicity of concrete individuals. Therefore, when we think of what is essential to an individual being (such as a human being) we may define the essence by reference to both the form and matter, if the latter is considered abstractly and universally, as a necessary constituent of the nature of such things. That is to say, each human being consists essentially of both form and matter, of soul and individual body, not merely of the soul. But the individual matter of Paul is not essential to any other human being, nor could it be (ST: q. 75, a. 4 [part I]; Summa Contra Gentiles [SCG]: c. 54 [part II]). It is human to have an individual body, then, but it is not essential to us as humans to have the body of another individual human distinct from ourselves. Given this way of thinking about the essences of individuals we experience in the material world, is it also then possible to think of God along these lines? Is God (the Lord God of Israel) one god among others, an individualized divine nature who shares the same nature and properties with other such beings, but who is individually distinct from the other gods?

Aquinas argues that this cannot be the case (ST: q. 3, a. 3 [part I]). God is not composed of matter and form, so he is individuated by his form alone. Otherwise stated, God is unique in virtue of his individual deity. He is the one God because he alone has the nature of God. Evidently this medieval scholastic idea aligns quite closely with the modern historical question we noted above pertaining to the development of Israelite religion. How, historically speaking, did ancient Israelites come to believe that Yhwh is the one true God? That question is genealogical and is related to ancient claims of prophetic revelation, while the question we are treating here is metaphysical, and has a philosophical dimension. Ultimately, however, the two topics are deeply related, since the genealogical question seeks to resolve the question of when and how the people of Israel came to the conviction of something like the idea formulated by Aquinas and other theologians in a more theoretical mode; namely that God alone is God, that he alone possesses the nature and attributes of the one God and Creator of all things.

This idea also has trinitarian consequences, since it suggests that if the three persons each possess the divine nature in its fullness, then they are not three individual beings, each having the divine nature in the same way three human persons have human nature, that is to say as distinct substances. Rather each has the fullness of the divine nature within his person, and thus they are each the one God, since there is no composition of nature and individual in God. The three persons are ‘consubstantial’.

4.2.3 Essence and existence

Aquinas posits a real distinction in all created beings of essence and existence (or esse in Latin) (De Ente et Essentia [DEE; see 1948]; SCG: c.52–54 [part II]; De Potentia Dei [QDP]: q. 7 [part 1] [see 1965]). Essence for Aquinas signifies the nature of a given thing. In material beings, the essence consists of both form and matter, where the latter is conceived of abstractly in universal terms. For example, it is not essential to all human beings to have the body of a given individual like Paul, nor could it be, but it is essential to all human beings to have a physical body as well as a soul. Therefore, the whole form-matter composite pertains to the essence of what it is to be human. In angelic realities, which are wholly immaterial, the essence pertains to the form alone, as each angel has a unique nature in virtue of its immaterial form, and not in virtue of an immaterial body.

Esse signifies the act of being, or singular existence, of a given individual substance (DEE: c.2, 5; QDP: q. 7, a. 2, ad 9). Each individual material essence (a human being or a horse or a tree) has an individual existence. This is true as well of each immaterial being (or angel); its existence is unique. Existence is thus common to all things in a way essence is not, since the many created realities in the world are of many different natural kinds (essences), but they all have existence in common. At the same time, existence is proper to each individual reality in a wholly unique way, as the singular existence of the archangel Gabriel is distinct from that of a man, a pine tree, or a blade of grass. No created reality is the cause of its own existence. Instead, we see that all realities around us, including ourselves, come into and can go out of existence, and they are both given existence and sustained in being due to the causal activity of others. Nothing in creation exists merely by nature, due to the kind of essence it has, such that it would exist by sheer primal necessity. Aquinas famously relates essence and existence in creatures to one another as potency is related to act. Each individual essence can be or not be, and thus is either in mere potency to exist or does truly exist. However, even when creatures do actually exist, they have the latent potency within them not to exist, in virtue of their created status.

Aquinas argues that this kind of composition of essence and existence that is found in all created realities cannot obtain in God or his divine nature (ST: q. 3, a. 4 [part I]). In differentiation from creation, God the Creator does not receive his being from another and is not caused to be. He simply is from all eternity and is the cause of all else that is. He communicates existence to others, from the abundance of his own infinite and perfect being, but his being is not received from, ontologically enriched by, or dependent upon, his interactions with his creatures. If this is the case, then God is incomprehensibly different from his creation. His divine essence alone exists by nature and is ontologically necessary in a way no created reality can be. His essence also contains the plenitude of all existence, since he is being essentially, in all that pertains to being, and all that comes to exist in creation comes from his prior actuality and perfection, and is a merely participated and imperfect expression of God’s transcendent nature (ST: q. 13, a. 11 [part I]). In God there is no ontological composition of essence and existence.

Evidently this idea is deeply related to the Old Testament notion we touched upon above, regarding the idea that the God of Israel alone is the Creator of all that is, ‘he who is’, (Exod 3:14–15; Isa 45; John 8:58) the one who gives being to all things. It also touches upon the idea in trinitarian theology that the Father, Son, and Holy Spirit each possess the plenitude of divine esse, and that they all therefore give rise together to all that exists apart from God. In short, all acts of the Holy Trinity ad extra (‘outside’ of God) in the creation and the redemption, are works of all three persons, since all three possess the one essence of God and thus the one divine existence (ST: q. 42 [part I]). They each possess that plenitude from which all things proceed and come forth in being, and by which all things are sustained in being. On this view, which is related logically to the doctrine of divine simplicity in the aforementioned respect, it is the Trinity that creates, sustains, and redeems all things in creation, and never merely one of the persons acting alone, as if the Father might act divinely as God and Lord, without the Son or the Spirit. The unity of trinitarian action and the doctrine of divine simplicity are deeply interrelated ideas (ST: q. 11, a. 3 [part I]).

4.2.4 Substance and accident

The final composition we will consider in this context pertains to substance and accidental property. As Aquinas notes, created realities are complex ontologically, since they are each composed of substance and accidents. That is to say, they have unity as individual substances (like a singular tree or a human) and they also have properties such as a given quantity, qualities, relations to other things around them, and so forth. Human qualities such as intelligence or moral excellence are not identical with the whole human substance (as if a person were their act of understanding or volition), but characterize human beings as important properties.

Following Augustine, Aquinas argues that this kind of ontological composition does not exist in the divine nature (ST: q. 3, a. 6 [part I]). One reason has to do with act and potency argumentation. A given substance that has accidental qualities is in ontological potency to have or not have the qualities in question, especially if these qualities emerge and develop dynamically. The divine nature however is not in potency to further development through a historicity of divine becoming and does not depend upon any other reality causally so as to develop in being (for example, through interaction with creation). Instead, what we call God’s ‘essence’ entails a numinous plenitude such that God is perfect in being from all eternity to all eternity (ST: q. 4 [part I]). A similar argument follows from the negation of the real distinction of essence and existence in God. If God possesses essentially, or by nature, the fullness of existence, and communicates being to all others as Creator, then God does not develop in existence progressively, as he would if he had something like the equivalent of accidental properties as they are found in human beings (ST: q. 3, a. 6 [part I]).

On this view, we may still affirm (along with Aquinas and other like-minded medieval theologians) that God actively knows and loves all that exists in the creation. Indeed, Aquinas argues at length that all that exists in creation comes forth into being from the knowledge and love that characterize the divine essence (ST: qq. 14, 19, 20 [part I]). Nevertheless, such knowledge and love of the divine nature are not like human understanding and loving, at least in this, that they are not enriched or historically qualified positively in a developmental fashion by engagement with creation. Rather, God creates out of the plenitude of eternal contemplation and love that characterizes his very nature as God (ST: q. 14, a. 8 and q. 20, a. 2 [part I]). Were this not the case and were God to learn experimentally from creation and grow in moral virtue through his engagement with it, then creation would in some sense actively qualify and cause God to be, and the two would necessarily exist within a larger co-constituting system, an idea that stands in tension with traditional biblical and patristic notions of Creator and creation.

As we have noted above, Augustine argues in a similar vein that God is not wise or good by qualification but that God is his goodness and wisdom. This idea has consequences for trinitarian theology in several ways. First, it means that one cannot differentiate the persons in God by appeal to distinct natural characteristics, as if God were powerful only in his paternity, wise only in his filiation, and good only in his spiration. Instead, all three persons partake of the plenitude of the divine essence and therefore also partake of the plenitude of all divine ‘qualities’, which are mysteriously identical with the essence of God (ST: q. 42, aa. 1 and 4 [part I]). The Father, Son, and Holy Spirit possess in equal and identical measure the power, wisdom, and goodness of God that characterize his essential life (ST: q. 39, aa. 7–8 [part I]). Second, the divine attributes, such as wisdom and goodness, must also be in some real sense identical with one another. What we perceive in creation as distinct features of human beings, such as knowledge and love, can and must be ascribed to the divine nature, but what we signify when we indicate them in God is something that is mysteriously one in God himself (ST: q. 13, aa. 2 and 4 [part I]). The divine simplicity, perfection, goodness, eternity, power and so forth, are identical in God, yet each of these terms helps us indicate more clearly what God is, even if his essence remains beyond our plenary comprehension. Finally, on this view, the persons in the Trinity cannot be distinguished by various qualities or accidental properties they acquire due to their respective actions in the economy of creation and salvation (this viewpoint contrasts notably with Rahner 2001: 24–30). For example, the Father is not differentiated from the Son by his unique qualifying action of creation while the Son is differentiated by his unique action of redemption or incarnation. Rather, the divine persons are at the origin of all that occurs in the economy of creation and they act in virtue of the essence they share as the one God. That action does not re-qualify or enrich them collectively or individually but is the expression of the plenitude of trinitarian life that they possess inalienably from eternity.

4.2.5 Trinitarian persons and divine simplicity

Aquinas’ theology of divine simplicity has a direct bearing on the way in which he conceives of the distinction of trinitarian persons. If the three persons are each the one God and subsist as the one God, then the real distinctions that obtain between them do not derive from the divine nature which they share but from the two processions of generation and spiration and from the relations of origin that these processions instantiate. The Father eternally begets the Son as his Word, and in so doing communicates to the Son all that he is and has as God (ST: q. 27, a. 2; qq. 33–34 [part I]). The Father and the Son eternally spirate the Holy Spirit as their reciprocal Love, and in so doing communicate to the Spirit all that they have and are as God (ST: q. 27, aa. 3–4; qq. 36–38 [part I]). The Son is thus related to the Father eternally as the one he originates from, and the Spirit likewise to the Father and the Son. Like other scholastics, such as Albert the Great and Bonaventure, Aquinas argues that the relations of origin in the Holy Trinity are not accidental properties of the persons but are mysteriously subsistent (ST: q. 29, a. 4 [part I]; Bonaventure, Commentaria in Quatuor Libros Sententiarum: d. 26, a. un, q. 3; Emery 2001: 455–465). The Father is his paternity; he is a principle of origin of the Son and the Holy Spirit in all that he is, as font of the trinitarian life. The Son is his filiation; he is from the Father and for the spiration of the Spirit in all that he is as Word. The Spirit is his spiration; he is a from the Father and the Son in all he is (ST: q. 33, a. 2 [part I]). Each person is truly God (having in himself the plenitude of the divine essence) and each person possesses his deity in a particular personal mode. He is God in either a paternal, filial, or spirated way (Emery 2005: 31–77). Such notions follow directly from the two-fold affirmation that (1) the divine essence is simple in the ways indicated above and (2) the three persons are one in essence (consubstantial, homoousios), in accord with the formulation of the Nicene creed (Emery 2000: 521–563).

This view of the trinitarian persons underscores both the relational primacy of the Father and the radical egalitarianism that obtains in God. The Father is the principle and font of trinitarian life, but he is not greater in nature or ontological stature than the Word or the Spirit, even if these two derive from him originally. Indeed, they receive eternally from him all that he is as God, in the simplicity and plenitude of his divine being and life. This affirmation does not negate or eclipse the real distinction of the persons in God or the interpersonal reality of their communion or their relationships with creatures, by grace. On the contrary, this way of indicating personal distinction in God augments a sense of their communion as mutual indwelling. The interpersonal communion of the Trinity implies a singular, shared, mutual essence of the one God present in all three persons (ST: q. 42, a. 5 [part I]). This means that by perichoresis, or mutual indwelling, the whole of ‘what’ the Father is, is in the Son and the Spirit, and the whole of what the Son is, is in the Father and the Spirit, and the whole of what the Spirit is, in his divine plenitude, is in the Father and the Son. This mutual indwelling is also accomplished from and in the living and eternal ‘cycle’ of trinitarian processions, so that the Father is in the Son and Spirit insofar as he communicates to them to be from him all that they are as God, yet in personal distinction. They likewise only have in themselves all that the other two do, either as one who receives all that he is from the Father and gives it to the Spirit with the Father (in the case of the Son), or as one who receives all that he has from the Father and the Son (in the case of the Spirit).

The distinction of persons in their self-communication to creatures by grace is also underscored by this doctrine of divine simplicity since it allows one to appreciate that when all three persons each act distinctly, they also always act with the other two. All actions of the Father, while paternal in mode, also imply common action of the Son and Spirit respectively, who act in their own irreducibly distinct personal modes of action. When one person is active in his distinctness, the other two must also be active in their relative modes of distinctness. If the Father communicates grace to a human person, in his distinctive mode as Father, then the Son also does so with him, in his distinctive mode as the begotten Son of the Father, and the Spirit in his distinctive mode as the spirated Love of the Father and the Son. Each person is truly God so that when we commune by grace with Jesus Christ, who is the Son of God, we also commune with one who, as God and Lord, is in perfect communion with the Father, indeed one in being with the Father, in the sense just indicated. In other words, communion with one person is always communion with that person in his personal action but it is also communion with the other two persons in their personal action, so that the reciprocity of interpersonal relationship with one person of the Trinity that grace effectuates in us, implicates personal relationship with the whole Trinity, as a communion of persons, and without conceiving of the latter in any way as a mere abstract essence.

4.3 Alternative medieval concepts

As noted above, the treatment of divine simplicity in Western medieval scholasticism is far from homogeneous. Although Aquinas’ conception of divine simplicity has been historically influential, alternative conceptions exist that have had similarly important influence in the Western theological tradition. Though they are each Franciscans, the distinctive and in some sense incompatible conceptions of John Duns Scotus and William of Ockham each deserve particular consideration in this respect.

Duns Scotus’ conception of divine simplicity can be helpfully contrasted with that of Aquinas in two ways. First, Duns Scotus posits, in keeping with Augustine and Aquinas, that God’s essence and nature is simple, in the sense that it is non-composite and individually unique. However, he retains what has come to be called ‘a formal distinction’ of the attributes of the one God. Aquinas held that our diverse ways of indicating God through divine names or attributes is semantically meaningful since each name denotes something true about God. Terms such as divine wisdom, goodness, justice, mercy, and so on, each say something true of God. However, these terms denote what is truly one and identical in God’s own essence, not formally or essentially distinct. What we call God’s wisdom, goodness, justice, and mercy are truly one in God’s own life and nature (ST: q. 13, aa. 2–4 [part I]). Duns Scotus, meanwhile, predicates these terms to God while underscoring that the attributes they specify in God are formally distinct, and not reducible to one another specifically in the eternal life of God. He does not predicate that they are accidental to one another, nor does he claim that they are properties of the essence. Like Augustine and Aquinas he denies this kind of composition in God, but his notion of simplicity is more ‘complex’ than that of Aquinas because he believes that the language we use for God’s essence when we employ terms for God must correspond in a partially univocal way to the very reality of God’s essence, and since we use distinct terms and each is posited univocally and truly of God in some sense, these distinctions in speech must correspond to something formally distinct in the nature of God (Duns Scotus, Ordinatio [Ord.]: 1.8.1.4, nos. 192–193 [in Opera Omnia: 261–262 [vol. 4]]; Cross 2005: 107–111, 235–240). Duns Scotus wants to underscore the harmony between our way of speaking of God and the very nature of God that we denote rightly in our speech.

This view of simplicity has significant consequences in Duns Scotus’ treatment of the trinitarian persons. Unlike Aquinas, who seeks to distinguish the persons of the Trinity primarily by reference to their relations of origin, Duns Scotus distinguishes the persons in part by recourse to the notion of distinct eternal natural actions of the person of the Father. Insofar as the Father naturally produces thought, through the essential activity of understanding, so he produces an immaterial Word (analogous to a concept) that is his natural offspring. This Word is infinite in perfection and consequently is a personal reality (since any reality that is infinite in perfection must be personal). Insofar as the Father naturally loves, through the essential activity of loving, he spirates the Spirit who is Love. This Love is infinite in perfection and consequently is a personal reality. The formal distinction of understanding and love that is applicable to God according to the distinction of attributes of the divine essence thus plays an important role in trinitarian theology. The Father is characterized by formally distinct natural actions that produce distinct persons. The logic of Duns Scotus’ position permits him to claim overtly that once one has identified the formally distinct attributes of the essence of God, and the naturally distinct operations that they imply, which are infinite in perfection, one can in turn demonstrate rationally by philosophical argument that there are eternal personal processions in God of Word and Love. While Aquinas argues that natural reason cannot demonstrate the existence of the Trinity as the mystery of the inner life of God (and so this has to be revealed to be known), Duns Scotus argues that there is some real possibility of natural knowledge of the trinitarian processions, based on his doctrine of formal distinction, and his mitigated reception of the doctrine of divine simplicity (Duns Scotus, Ord.: 1.2.2.1–4, nos. 221–222, 226, 355–356 [Opera Omnia: 259–263, 336 [vol.2]]; Cross 2005: 132–142, 153–155). Duns Scotus’ theology thus appears less apophatic than that of Aquinas, suggesting a marked confidence in the natural dispositions of human reason to attain understanding about God’s inner life as Trinity, as reflected both in the doctrine of univocal divine names and the theory of formal distinction.

Ockham’s position on divine simplicity is in many respects the inverse of Duns Scotus’. Ockham posits that there is such a marked notion of divine simplicity that obtains when one thinks of God that it is difficult to entertain the very notions of eternal processions and distinction of persons in God. If God is simple, how can God be understood as a Trinity? Ockham problematizes the traditional Augustinian notion of a ‘psychological similitude’ that conceives of the two processions of the Word and Spirit by comparison to human mental acts of understanding and love, respectively. This similitude is not intelligible for Ockham, in light of the doctrine of divine simplicity, except as something akin to a metaphor (Ockham, Ord.: d. 2, q. 1 [Opera theologica [oTh.]: d. 1, q. 6 [vol. 2]; oTh.: d. 7, q. 2 [vol. 1]; oTh. [vol. 3]; Friedman 2010: 124–131). The reason is that everything that is found in one divine person is found in another, if they are truly one in essence, and the activities of understanding and will are proper to each person so they cannot be distinguished by such activities. The Church affirms that there is a distinction of persons in God according to relation of origin, and so Ockham derives a way to affirm nominally a set of propositions about the Trinity that are logically consistent. He is reticent, however, about our capacity to attain to any true knowledge of the eternal processions of the Trinity in this life (whether analogically or univocally). This reservation is related to his notion of divine simplicity.

Another alternative is presented by the fourteenth-century Byzantine theologian, Gregory Palamas, who distinguishes between the essence and energies of God. This distinction has applications in Gregory’s theology of grace and divinization. By God’s gift, human beings are invited to participate in the energies of God, but they are not able to apprehend or to enjoy any immediate spiritual communion with his essence, even in heaven. They do participate in the life of God in himself, but under a condition (see Gregory Palamas, The Triads: 93–112). This view is influential with some Eastern Christians and can be associated logically with those who are critical of the Filioque, the affirmation of the procession of the Spirit from the Father and the Son. Some Western theologians like Augustine, Anselm, and Aquinas (in differing ways) distinguish the Son from the Spirit based on relations of origin, and so they underscore that there must be a relation of origin of the Spirit from the Son. Eastern theologians inspired by Palamas, who posit a highly qualified concept of divine simplicity, may accept the Cappadocian notion of the generation of the Son from the Father and of the procession of the Spirit from the Father without feeling constrained by the Western concept of the doctrine of simplicity to resolve the question of the relation of the Son to the Spirit (the relation of origin between them) (see Papademetriou 2004: 77–94). Therefore, they may argue that the absence of distinction between essence and energies in Western theology (and the corresponding notion of God’s essence as non-composite) is logically related to the Western affirmation of the Filioque. Furthermore, some argue (paradoxically) that the Western concept of simplicity leads to pantheism, since it somehow implies that God’s essence is identical with his energies, and thus God is identical with his activity in the world (see Lossky 1997: 73–75). This latter claim seems to brazenly ignore clear conceptual arguments to the contrary.

4.4 Classical Reformation notions

Neither Martin Luther nor John Calvin produced extensive reflections on the concept of divine simplicity. Luther does insist thematically on God’s hiddenness and his inaccessibility to all merely human modes of knowledge, which some see as implying a notion of divine simplicity (see Hoyum 2020). Calvin, meanwhile, unambiguously underscores God’s simplicity in the context of his discussions of the equality, unity and real distinction of the trinitarian persons (Institutes of the Christian Religion [ICR]: 1.13.2). Their respective presentations of trinitarian theology are often modest when it comes to reflection on the inner life of the processions of the persons, a reserve that is perhaps indicative of a measured acceptation of the trinitarian reserve of Ockham mentioned above. Instead of focusing on the immanent life of the Trinity, their theologies indicate truths of revelation manifest especially in light of the incarnation, life, atonement, and resurrection of Jesus of Nazareth. However, later Protestant scholastic theology, particularly in the Reformed tradition, made appeal to the notion of divine simplicity in a more thematic fashion, and the idea is present in various confessional decrees in the Lutheran, Reformed and Anglican traditions respectively, such as those of the Augsburg Confession, the Belgic Confession, the Thirty-Nine Articles of Religion, the Westminster Confession of Faith, the Savoy Declaration, and the Second London Confession of Faith. These statements typically underscore at the very least that the divine nature is non-bodily (without parts) and one, in addition to being good, infinite, eternal, and characterized by activities of knowledge and love that are not historically complex and developmental in the way those of human beings are.

5 Modern trends

5.1 Spinoza and Hegel

The seventeenth-century philosophy of Baruch Spinoza presents a potential challenge to theories of divine simplicity, particularly through its contestation of traditional theistic notions of God. Interpretations of Spinoza’s Ethics are famously controverted. However, it is clear that he posits in the First Part that God is best understood uniquely by recourse to philosophy (and not revelation), and that God is defined as the causal source of the natural world, to whom all entities or characteristics of nature are attributed as properties are attributed to a solitary substance (Ethics: Proved in Geometrical Order, First Part: propositions 1–15). Furthermore, the natural world emerges from God by necessity, and is in a sense identical with God as a single subject to whom an infinite number of properties found in nature may be attributed, realities studied by the natural sciences and rational philosophy (Ethics, First Part: propositions 16–18). Whether Spinoza is a pantheist or an atheist, his decision to redefine ‘God’ in naturalistic terms effectively renders the first principle co-extensive with the material cosmos. Spinozist metaphysics thus posits a universe that is one, but that is not simple. Nature is a unity of parts that can be explained by recourse to a unified system of causal necessities, studied by scientifically informed natural philosophers. We might speak here of a total unity of composition that is transparent to reason, and thus in a sense comprehensively simple, both ontologically and logically. This last point is important, since Spinoza wishes to reject systematically any recourse to supernatural revelation in order to explain the world; natural reason suffices to understand everything. One can argue, however, that the problem then emerges of what is primary: the reason of the universe that informs matter, or the materiality of the universe that gives rise to mind. Nature, or ‘God’, seems somehow to consist in both.

In the nineteenth century, Hegel, inspired by Spinoza, seeks to provide a post-Enlightenment metaphysical analysis of world history that is philosophical and all-comprehensive. But he takes a different approach to Spinoza, making use both of dogmatic Christian resources, as well as pre-modern philosophical resources, such as the thought of Aristotle. From Aristotle, Hegel takes up the notion of God as thought thinking itself and the conception of teleology, which Spinoza rejected. However, he reinterprets these Aristotelian notions historically, and sees God’s own intellectual actualization as occurring in and through the history of created reality, not only in the physical cosmos and animal life, but especially in the spirit and culture of human persons (art, politics, religion, and philosophy) (Hegel 2018: 454–467). The composite unity of God and the world that one finds in Spinoza’s naturalism is thus rethought in historical terms by appeal to an immanentistic dynamic, the unfolding of divine spirit in and through the history of human spirit. Furthermore, this understanding of God is interpreted in overtly trinitarian terms. The traditional doctrinal depictions of God as Father, Son, and Holy Spirit are religious representations of an earlier stage of human reflection, one that come to maturity when recast in distinctly philosophical terms. The Father represents divine Spirit prior to the unfolding of the history of the world, while the Son represents eternal Spirit in its free self-emptying identification with the contrary attributes of finitude and temporality, as well as subjection to non-being. God the Holy Spirit represents the reconciliation of the dialectical movement in God to self-identify with God’s contrary, and so, historical Spirit that is not merely finite or infinite, temporal or eternal, but all these things simultaneously, reconciled within the context of a greater teleological whole. God will become all in all, and in so doing will become God’s plenary self. This final state concludes with the emergence within history of a human culture of rational perfection, one that attains a rational coherence with God (the immanent and transcendent principle of all history) (Hegel 2006: 426–490). Hegel thinks that this age of the Spirit is manifest in modern society through liberal democratic freedom, where Enlightenment philosophical education is placed at the service of international order. This ‘end of history’ is the age of the Holy Spirit.

5.2 The First Vatican Council

The First Vatican Council reaffirmed the Catholic Church’s theological commitment to a doctrine of divine simplicity in 1870 in the dogmatic constitution Dei Filius (chapter 1; First Vatican Council 1990: 805 [vol. 2]). In historical context, this document seeks to exclude a pantheistic conception of the deity or the cosmos, associated at the time with the philosophies of Spinoza and Hegel. In doing so it sought to underscore the continued philosophical viability of classical metaphysics, and the theological normativity of classical conceptions of the Trinity inherited from thinkers like Augustine and Aquinas. As we have noted above, various classical scholastic schools in the Western and Eastern traditions promoted diverse accounts of the simplicity of the divine nature of the Trinity. The Council was not seeking to adjudicate between various patristic traditions or scholastic schools but instead sought to affirm in a general way the classical affirmation of the mysterious transcendence, eternity and immutable identity of the one God, over against competing conceptions of God as historical or ontologically composite with creation. This Catholic restatement of the mystery of divine transcendence is closely related logically to the claim of the council that belief in God is reasonable and that God’s existence can be demonstrated by natural reason. The human person is orientated by its intellectual nature toward an encounter with the transcendent mystery of God. Accordingly, modern and contemporary Catholic authors from a variety of schools have sought to present anew, explain, and defend a vibrant notion of divine simplicity (Scheeben 1948; Garrigou-Lagrange 1938; Emery 2007; Stump 2006; Te Velde 2006; Herrara 2011; Humbrecht 2011; Bonino 2016b. See also the Thomistic reflections of Kretzmann 1997). Contemporary Protestant philosophers and theologians have often followed suit, by seeking to underscore the essential role that the affirmation of divine simplicity plays in classical Reformed notions of God as transcendent Creator and as Trinity (see, for example, Dolezal 2011; Duby 2016; Vidu 2021).

5.3 Modern continental trinitarian trends

In mainstream modern continental theology, however, alternative trends have emerged. One might summarize this situation by arguing that divine freedom has come to play the role in modern trinitarian theology that divine simplicity plays in classical trinitarian thought. Hegel’s understanding of the Trinity is a remote influence in this respect. For Hegel, as we have noted, the Trinity is a pre-Enlightenment dogmatic religious representation that can be reconceptualized philosophically, so as to indicate the ontological process that is at the heart of reality. That is the process of the diremption of absolute spirit by which God self-identifies freely with contraries to God’s own self, and eventually achieves reconciliation with God’s self in and through a historical process of development. God represented as Father is impassible, eternal and infinite, while God represented as Son is subject in his very deity to temporality, finitude, death, and non-being. The Holy Spirit represents a new configuration of deity in which these two polarities of God explored in divine freedom achieve a new synthesis of greater rational plenitude, in and through the history of God’s being as finite, as absolute spirit within temporal human historical spirit.

Modern trinitarian theologians typically disavow the rationalism and pantheistic tendencies of Hegel, and maintain the transcendence of God as Creator and redeemer, as one who gives being to all things and redeems all things in Christ out of the plenitude of his pre-existent, eternal life and inalienable creative power. However, in their ‘corrective’ to Hegel they also typically affirm that God in his transcendence does have the freedom to identify with or to subject himself to his ontological contrary, without ceding his eternal and divine identity (White 2022: 397–399, 555–558). Thus, for thinkers like Moltmann and Jenson, God can be subject to historicity, passibility or suffering even within his own being and essence as God (particularly in the incarnation), and in doing so achieves a kind of di-polarity of freedom. He is free to exist simultaneously as eternal and temporal, impassible and suffering, immutable and mutable, and so forth (Jenson 2001: 66; Moltmann 1974: 202–203). Evidently this kind of historical vision of God as freely kenotic and as able to exist in distinct modes is a vision of God as ontologically composite and not simple, at least not in the ways envisaged above. More moderate versions of this thesis affirm that God’s human mode of being in the incarnation, in which the Son as man is humanly subject to the Father in obedience, suffering, and death, are indicative of di-polar modes of being in the Trinity that pre-exist the human modes and that are analogous to them. So Barth posits a divine obedience in God of the Son to the Father that is constitutive of the life of God from all eternity, thus indicating a kind of composite nature in God, wherein God as Father has natural qualities of willing distinct from, and juxtaposed to, those of the Son (Barth, Church Dogmatics [CD]: 4:1, Section 59: 157–357, especially 177–201 [see 1936]). Bulgakov and von Balthasar, meanwhile, posit an eternal kenosis in God that precedes and is the exemplar for the kenosis of the passion, wherein the Son undergoes human death freely (Bulgakov 2008: 98–99; Von Balthasar 1994: 319–333 [vol. 4]). The Son in his eternity is subject as God to a mystery of self-emptying, mirrored by the Father’s eternal self-emptying in generating the Son. The Spirit emerges from the two as the fruit of this mutual communion of free self-diremption (Von Balthasar 1992: 183–191, 521–523 [vol. 3]). If such ideas are to be taken as something more than metaphorical depictions of the divine processions, then they would seem to entail states of potency and actuation that are really distinct from one another in God, and that are present in the divine nature as it unfolds in a ‘pre-history’, one that constitutes the distinct persons eternally as they undergo the fluctuations of their various natural modes of being. Under such conditions one can speak of an eclipse or of a conceptually strategic abandonment of the theology of divine simplicity in modern mainstream continental trinitarian theology.

It should be noted in this context that the thinkers mentioned above are seeking to conserve many traditional Christian ideas regarding the mystery of the Trinity, and to do so by translating the doctrine into a modern intellectual idiom, making use of (and reacting against) certain versions of post-Enlightenment ontology. They are beholden in this respect to various continental ontologies, but not in an uncritical way. They accept elements of Spinoza’s and Hegel’s break with pre-modern forms of metaphysics and embrace their notion of the world and human culture as an unfolding and evolving process from and in God. They also maintain Hegel’s strategy of rehabilitating teleology and placing it in God (by positing the realization of act-potency composition in God) and like him they also seek to identify who God is by focusing on the unfolding dynamic of God in history. However, they distance themselves, in part at least, from the pantheistic connotations of Spinoza and Hegel, and argue instead that creation depends utterly upon God for its being, even if God determines himself freely in relation to the creation. What unfolds in the economy of trinitarian creation and redemption then (the historical dynamic of the so-called economic Trinity) corresponds to the pre-existent and final teleological life of God (the uncreated, eternal dynamism of the immanent Trinity).

5.4 Some analytic objections and responses

Modern analytic philosophers who are theists sometimes object to the doctrine of divine simplicity for a variety of alternative reasons. Some, such as Alvin Plantinga (1980), note that the notion of simplicity entails that all the divine attributes are identical with the essence of God. They object to this idea because they think that it naïvely reifies human, abstract notions, such as goodness or wisdom, so as to identify them mistakenly with the essence of God. This way of thinking would misguidedly project onto God a merely human abstract, logical way of thinking, one analogous to the Platonic theory of forms, which projects universal human concepts problematically onto individuals and onto the causal structure of reality. Understood in this way, divine simplicity is a construct of human logic and has no place in realistic discourse pertaining to God. Second, some philosophers worry that the notion of subsistent relations in trinitarian theology is incoherent, since relations, as they understand them, are either mere properties or are abstract entities (relation-sets of human logic) and not something real in themselves. Richard Swinburne (1994: 125–191), for example, depicts the three persons of the Trinity as three perpetually co-existent individual centres of consciousness related to one another by causal origin and by a moral consensus of cooperation. This vision of the Trinity is ontologically complex on many levels. Finally, and most commonly, many analytic theists worry that the notion of the divine simplicity is incompatible with a God who knows and loves, and who stands in real relation to his creation, makes choices, adjusts or responds to human behaviour, and so forth. All engagements of God with creatures by way of knowledge and love must entail change in God, and thus invite us to disavow the doctrine of divine simplicity. William Hasker (2016: 699–725) writes against the doctrine of divine simplicity for this reason, arguing that God must alter internally and perhaps develop in perfection over time, based upon his real relations with creation.

While a thorough consideration of such positions exceeds the scope of this article, it should be noted that proponents of the classical doctrine of divine simplicity have developed a variety of responses such objections. Here we may indicate briefly some of their arguments. First, in response to Plantinga, it has been pointed out that the concepts we use to denote God’s essence, such as goodness and wisdom, are abstract, but the process by which we qualify such concepts analogically so as to rightly denote God in himself entails that we acknowledge God’s singular transcendence and distinctiveness as one who is the author of all that exists and therefore as one who is not caused and composite in the ways creatures are. The doctrine of simplicity then entails a careful analysis of the conditions under which it is permissible and even required to use property terms abstractly to denote the individual personal being of God, much as one may denote atomic structures in matter under the rubric of waves and particles simultaneously, while accepting the limitations of language and human concepts when doing so (Stump 2016b: 191–210). Second, the attribution of relations to the persons of the Trinity in a subsistent mode is based on the idea that mutual relativity emerges from the simultaneity of action and passion (Emery 2007: 78–102). As the Father eternally begets the Son, so the Son is begotten of the Father, and in this respect, they are mutually related to one another in all that they each are, in an ontologically reciprocal way. This idea in itself is not incoherent, and therefore its use is logically consistent with the simultaneous affirmations that God is one, and that there are real relations in God. The fact that we never encounter such substantial relations in any created reality only serves to underscore the radical transcendence, alterity, and incomprehensibility of the trinitarian communion of persons, but it does not make that communion wholly unintelligible to us. The notion of subsistent relations is an analogical one, that takes created relations and created substances and transposes something of each onto God by similitude while simultaneously respecting the greater dissimilitude of God with respect to each. The doctrine of divine simplicity plays a helpful role in this process since it invites one to acknowledge that each divine person is the one God, even while being distinct from the other two persons by relations of origin (White 2016: 66–93). Third, it is true that affirmations of divine simplicity of the kind noted above do entail the negation of compositions of act and potency in God such that God’s life would change progressively or develop qualitatively in virtue of his engagements with creatures. It does not, however, entail the negation of the ascription of choice to God, in relation to creatures, or of knowledge of creatures in God (SCG: c. 10–23 [part III]). It does ensure that when theologians speak of God knowing the world or loving the world or choosing to act in this or that way, they do so while recognizing that God’s knowledge and decrees stem from, and express his purely actual plenitude of perfection and fullness of existence (Dodds 2008: 161–237). In this sense, God’s knowledge and love and choice-making for creation stem from within his eternity and encompass an eternal awareness of all that is in creation, in its temporality and development. His action in the world stems from his perfection, that always, already ‘encompasses’ all created historical being. This does not mean God cannot ‘react’ to creatures in new temporal initiatives, but only that when he does so, such actions occur mysteriously in light of God’s eternal knowledge and love of himself and of the whole of his creation (Stump 2016a). Nor need this view lead to the denial of free will in creatures, since God’s creative knowledge is the source of the real and historically contingent freedom of creatures, which God in his simplicity sustains in being, and protects in his providence (Dodds 2008: 170–183; Bonino 2016b: 289–296, 676–682).

6 Conclusion

The controversies over divine simplicity are of conceptual importance. Although some may discount any appeal to this traditional idea, it arguably arises within Christian history as a way to reflect on themes in biblical literature. The mystery of God, the divine nature, is not a composite body, an individual of a given kind who shares in deity with others, a being who receives existence from others or participates in being, or a substance subject to historical alterations under the influence of actions effectuated by others. When promoters of the notion of divine simplicity deny such compositions of God, they wish to underscore his transcendence and numinous alterity, so as to indicate obliquely in human language he from whom all created things proceed and have being, and who is not himself created.

The doctrine is deeply related to the notion of divine unity since it is employed to underscore God’s essential perfection, fullness of being, and immutable identity, attributes in virtue of which God is eternally unique and one, in his incomprehensible existence.

Such ideas also have profound consequences for one’s theological reflection on the mystery of the Trinity. As patristic and scholastic authors have underscored, the nature of God is present in its fullness in each person of the Trinity, so that each is personally the one God. Therefore, the three persons are not distinguished by nature or by properties of the divine nature. Rather they are rightly distinguished, on this view, by relations of origin, through eternal generation and spiration. This understanding of the Trinity entails the idea that the three persons are each truly distinct, but also each equally and identically God, so that what results from the affirmation of divine simplicity is, arguably, a highly coherent notion of trinitarian monotheism. Each person can be understood as a possessing a distinct personal mode of subsistence, or personal way of being God, in virtue of the relations of origin, even while having the fullness of the deity as the subsistent God. Therefore, each divine person exists only ever in real relation to the others even while also possessing in himself all that pertains to the others as God, in virtue of the divine essence that is common to the three.

Promoters of the doctrine of divine simplicity hold diverse views and sometimes draw divergent conclusions from appeal to the notion. Critics of the notion are equally diverse and continue to raise a variety of excellent challenges to the idea. This all being said, the notion of divine simplicity is at the centre of ancient biblical and patristic thinking about the Trinity and is at the core of a great deal of traditional theological thinking. Those who reject the idea sometimes generate very original theologies of God, but also ones often riddled with significant conceptual difficulties. For these various reasons, the notion of divine simplicity will continue to be a mainstay consideration of Christian theology, especially in reflections pertaining to the Trinity, the doctrine of God, reasonable biblical interpretation, and the role of philosophical theology within Christian theology. Having recently been subject to a historical eclipse, the doctrine of divine simplicity seems to be re-emerging gradually in contemporary theology, and shining anew, like the risen Son, who is eternally simply one in being with his Father.

Attributions

Copyright Thomas Joseph White O.P. ORCID logo (CC BY-NC)

Bibliography

  • Further reading

    • Bonino, Serge-Thomas. 2016b. Dieu, ‘Celui Qui Est’; De Deo ut Uno. Paris: Parole et Silence.
    • Friedman, Russell L. 2012. Intellectual Traditions at the Medieval University: The Use of Philosophical Psychology in Trinitarian Theology Among the Franciscans and Dominicans, 1250–1350. 2 vols. Leiden: Brill.
    • Hughes, Christopher. 1989. On a Complex Theory of a Simple God: An Investigation in Aquinas’ Philosophical Theology. London/Ithaca, NY: Cornell University Press.
    • Long, D. Stephen. 2016. The Perfectly Simple Triune God: Aquinas and His Legacy. Minneapolis: Fortress Press.
    • Radde-Gallwitz, Andrew. 2009. Basil of Caesarea, Gregory of Nyssa, and the Transformation of Divine Simplicity. Oxford: Oxford University Press.
    • Stump, Eleonore. 2006. Aquinas. London: Routledge.
    • Weigel, Peter. 2008. Aquinas on Simplicity: An Investigation into the Foundations of His Philosophical Theology. Bern: Peter Lang.
    • White, Thomas Joseph. 2022. The Trinity. Washington, D.C.: The Catholic University of America Press.

  • Works cited

    • Aquinas, Thomas. 1888–1906. Summa Theologiae. Sancti Thomae Aquinatis opera omnia. Volume 4. Rome. Leonine.
    • Aquinas, Thomas. 1918–1930. Summa Contra Gentiles. Sancti Thomae Aquinatis opera omnia. Volume 13. Rome: R. Garroni. Leonine.
    • Aquinas, Thomas. 1948. ‘De Ente et Essentia’, in Opuscula philosophica. Volume 1. Edited by R. Spiazzi. Turin/Rome: Marietti.
    • Aquinas, Thomas. 1954. ‘De Principiis Naturae’, in Opuscula Philosophica. Edited by Raimondo M. Spiazzi. Turin: Marietti.
    • Aquinas, Thomas. 1965. ‘Quaestiones disputatae de potentia Dei’, in Quaestiones disputatae. Edited by P. M. Pession. Turin/Rome: Marietti.
    • Aristotle. 1995. ‘Metaphysics’, in The Complete Works of Aristotle. Edited by J. Barnes. Translated by W. D. Ross. Princeton: Princeton University Press.
    • Augustine of Hippo. 2012. The Trinity. Translated by Edmund Hill. Hyde Park, NY: New City Press.
    • Ayres, Lewis. 2004. Nicaea and Its Legacy: An Approach to Fourth-Century Theology. Oxford: Oxford University Press.
    • Barnes, Michel René. 2009. ‘Irenaeus’ Trinitarian Theology’, Nova et Vetera 7, no. 1: 67–106. English edition.
    • Barr, James. 1959. ‘Theophany and Anthropomorphism in the Old Testament’, in Congress Volume: Oxford 1959. Vetus Testamentum Supplements 7. Edited by G. W. Anderson, P. A. H. de Boer, G. R. Castellino, H. Cazelles, E. Hammershaimb, et al. Leiden: Brill, 31–38. https://doi.org/10.1163/9789004275300_004
    • Barth, Karl. 1936–1975. Church Dogmatics. 4 vols. Edited and translated by G. W. Bromiley and T. F. Torrance. Edinburgh: T&T Clark.
    • Bauckham, Richard. 2008. Jesus and the God of Israel: God Crucified and Other Studies on the New Testament’s Christology of Divine Identity. Grand Rapids: Eerdmans.
    • Bonaventure. 1882–1889. Commentaria in Quatuor Libros Sententiarum. 4 vols. Ad Claras Aquas, Quaracchi: Prope Florentiam Ex Typographia Collegii S. Bonaventurae.
    • Bonino, Serge-Thomas. 2016a. Angels and Demons: A Catholic Introduction. Translated by M. J. Miller. Washington, D.C.: The Catholic University of America Press.
    • Bonino, Serge-Thomas. 2016b. Dieu, ‘Celui Qui Est’; De Deo ut Uno. Paris: Parole et Silence.
    • Brueggemann, Walter. 2012. Theology of the Old Testament: Testimony, Dispute, Advocacy. Minneapolis: Fortress.
    • Bulgakov, Sergei. 2008. The Lamb of God. Translated by Boris Jakim. Grand Rapids: Eerdmans.
    • Calvin, John. 1960. Institutes of the Christian Religion. 2 vols. Edited by John T. McNeill. Translated by Ford Lewis Battles. Philadelphia: Westminster Press. First published 1559.
    • Cross, Richard. 2005. Duns Scotus on God. Aldershot: Ashgate.
    • Dodds, Michael J. 2008. The Unchanging God of Love: Thomas Aquinas and Contemporary Theology on Divine Immutability. Washington D.C.: The Catholic University of America Press.
    • Dolezal, James E. 2011. God Without Parts: Divine Simplicity and the Metaphysics of God’s Absoluteness. Eugene, OR: Pickwick Publications.
    • Duby, Steven J. 2016. Divine Simplicity: A Dogmatic Account. London: Bloomsbury T&T Clark.
    • Duns Scotus, John. 1950–2013. Opera Omnia. Edited by C. Bali. Rome: Typis Polyglottis Vaticanis.
    • Emery, Gilles. 2000. ‘Essentialism or Personalism in the Treatise on God in St Thomas Aquinas’, The Thomist 64, no. 4: 521–563.
    • Emery, Gilles. 2001. ‘La relation dans la théologie de saint Albert le Grand’, in Albertus Magnus: Zum Gedenken nach 800 Jahren: Neue Zugänge, Aspekte und Perspektiven. Edited by O. P. Walter Senner. Berlin: Akademie Verlag, 455–465.
    • Emery, Gilles. 2005. ‘The Personal Mode of Trinitarian Action in Saint Thomas Aquinas’, The Thomist 69, no. 1: 31–77.
    • Emery, Gilles. 2007. The Trinitarian Theology of Saint Thomas Aquinas. Translated by F. Murphy. Oxford: Oxford University.
    • Evans, G. R. 2000. Bernard of Clairvaux. Oxford: Oxford University Press.
    • First Vatican Council. 1990. ‘Dei Filius’, in Decrees of the Ecumenical Councils. Edited by Norman P. Tanner. Washington, DC: Georgetown University.
    • Friedman, Russell L. 2010. Medieval Trinitarian Thought from Aquinas to Ockham. Cambridge: Cambridge University Press.
    • Garrigou-Lagrange, Reginald. 1938. De Deo Uno. Paris: Desclée et Brouwer.
    • Gilbert of Poitiers. 1966. ‘Expositio in Boecii de Trinitate’, in The Commentaries on Boethius by Gilbert of Poitiers. Edited by N. Häring. Toronto: Pontifical Institute of Medieval studies.
    • Gregory of Nazianzus. 1994a. ‘Oration 29’, in A Select Library of the Nicene and Post-Nicene Fathers of the Christian Church. Volume 7. Edited by Philip Schaff and Henry Wace. Translated by C. G. Browne and J. E. Swallow. Peabody, MA: Hendrickson Publishers.
    • Gregory of Nazianzus. 1994b. ‘Oration 31’, in A Select Library of the Nicene and Post-Nicene Fathers of the Christian Church. Volume 7. Edited by Philip Schaff and Henry Wace. Translated by C. G. Browne and J. E. Swallow. Peabody, MA: Hendrickson Publishers.
    • Gregory of Nyssa. 2004a. ‘Against Eunomius’, in A Select Library of the Nicene and Post-Nicene Fathers of the Christian Church. Volume 5. Edited by Philip Schaff and Henry Wace. Translated by W. Moore and H. A. Wilson. Peabody, MA: Hendrickson Publishers.
    • Gregory of Nyssa. 2004b. ‘Not Three Gods’, in A Select Library of the Nicene and Post-Nicene Fathers of the Christian Church. Volume 5. Edited by Philip Schaff and Henry Wace. Translated by W. Moore and H. A. Wilson. Peabody, MA: Hendrickson Publishers.
    • Hasker, William. 2016. ‘Is Divine Simplicity a Mistake?’, American Catholic Philosophical Quarterly 90, no. 4: 699–725.
    • Hegel, Georg W. F. 2006. ‘The Consummate Religion’, in Lectures on the Philosophy of Religion, the Lectures of 1827. Volume 3. Edited by P. C. Hodgson. Translated by R. F. Brown, P. C. Hodgson, and J. M. Stewart. Berkeley, CA: University of California.
    • Hegel, Georg W. F. 2018. The Phenomenology of Spirit. Translated by T. Pinkard. Cambridge: Cambridge University Press.
    • Herrara, Juan José. 2011. La simplicidad divina según santo Tomás de Aquino. Salta, Argentina: Ediciones de la Universidad del Norte Santo Tomás de Aquino.
    • Hoyum, John W. 2020. ‘Luther and Some Lutherans on Divine Simplicity and Hiddenness’, Lutheran Quarterly 34, no. 4: 390–409.
    • Humbrecht, Thierry-Dominique. 2011. Trinité et Création au Prisme de la Voie Négative chez Saint Thomas d’Aquin. Paris: Parole et Silence.
    • Irenaeus. 2004. ‘Against Heresies’, in Ante-Nicene Fathers. Volume 1. Edited by A. Roberts and J. Donaldson. Peabody, MA: Hendrickson Publishers.
    • Jenson, Robert. 2001. Systematic Theology, Vol. 1: The Triune God. Oxford: Oxford University.
    • Kretzmann, Norman. 1997. The Metaphysics of Theism: Aquinas’s Natural Theology in Summa Contra Gentiles I. Oxford: Clarendon Press.
    • Lossky, Vladimir. 1997. The Mystical Theology of the Eastern Church. Yonkers, NY: SVS Press.
    • Miller, Patrick D. 2000. The Religion of Ancient Israel. Louisville, KY: Westminster John Knox.
    • Moltmann, Jürgen. 1974. The Crucified God: The Cross of Christ as the Foundation and Criticism of Christian Theology. Translated by R. A. Wilson. San Francisco: Harper & Row.
    • Palamas, Gregory. 1983. The Triads. Translated by N. Gendle. Mahwah, NJ: Paulist Press.
    • Papademetriou, George C. 2004. Introduction to St. Gregory Palamas. Brookline, MA: Holy Cross Orthodox Press.
    • Plantinga, Alvin. 1980. Does God Have a Nature? Milwaukee: Marquette University.
    • Plotinus. 2019. Enneads. Translated by G. Boys-Stones, J. M. Dillon, L. P. Gerson, R. A. H. King, A. Smith, et al. Cambridge: Cambridge University Press.
    • Rahner, Karl. 2001. The Trinity. Translated by J. Donceel. London: Continuum.
    • Scheeben, Matthias. 1948. Handbuch der katholischen Dogmatik, vol. II: Gotteslehre oder die Theologie im engeren Sinne. Freiburg im Breisgau: Herder.
    • Smith, Mark. 2003. The Origins of Biblical Monotheism: Israel’s Polytheistic Background and the Ugaritic Texts. Oxford: Oxford University.
    • Smith, Mark. 2016. Where the Gods Are. New Haven, CT: Yale University.
    • Spinoza. 2018. Ethics: Proved in Geometrical Order. Translated by M. Silverthorne. Cambridge: Cambridge University Press.
    • Stump, Eleonore. 2006. Aquinas. London: Routledge.
    • Stump, Eleonore. 2016a. ‘Simplicity and Aquinas’s Quantum Metaphysics’, in Die Metaphysik Des Aristoteles Im Mittelalter: Rezeption Und Transformation. Edited by Gerhard Krieger. Berlin: De Gruyter.
    • Stump, Eleonore. 2016b. The God of the Bible and the God of the Philosophers. Milwaukee: Marquette University.
    • Swinburne, Richard. 1994. The Christian God. Oxford/New York: Clarendon Press. 1st edition.
    • Tanner, Norman P. (ed.). 1990. Decrees of the Ecumenical Councils. 2 vols. Washington, D.C.: Georgetown University Press.
    • Te Velde, Rudi. 2006. Aquinas on God. The ‘Divine Science’ of the Summa Theologiae. London: Routledge.
    • Vidu, Adonis. 2021. The Same God Who Works in All Things: Inseperable Operations in Trinitarian Theology. Grand Rapids: Eerdmans.
    • Von Balthasar, Hans Urs. 1992. Theo-Drama: Theological Dramatic Theory, Vol. 3: Dramatis Personae: Persons in Christ. Translated by G. Harrison. San Francisco: Ignatius.
    • Von Balthasar, Hans Urs. 1994. Theo-Drama: Theological Dramatic Theory, Vol. 4: The Action. Translated by G. Harrison. San Francisco: Ignatius.
    • White, Thomas Joseph. 2016. ‘Divine Simplicity and the Holy Trinity’, International Journal of Systemic Theology 18, no. 1: 66–93.
    • White, Thomas Joseph. 2022. The Trinity. Washington, D.C.: The Catholic University of America Press.
    • William of Ockham. 1967–1986. Opera theologica. St. Bonaventure, NY: Franciscan Institute.

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