This study examines how early Christian theologians in the ante-Nicene period appropriated the philosophical concept of divine simplicity to present a coherent understanding of God in response to contemporary heresy. This appropriation led to the emergence of the “trinitarian problematic” of how to reconcile notions of divine simplicity with the scriptural revelation of God as Father, Son, and Holy Spirit. The author seeks to uncover the “doctrinal ecology” of the second and third centuries that gave rise to this problematic and its complex solution in the thought of Origen of Alexandria.

Chapter 1 examines the locus classicus of divine simplicity in Plato's Republic, highlighting that in Republic 380d–383c, metaphysical and ethical notions of simplicity are linked. The author argues that this feature allows for an understanding of the divine not simply or solely as a numerical unit, but as self-consistent, a consideration that in the thought of later theologians will allow the Christian God to incorporate some measure of multiplicity. Chapter 2 considers how the simple God of Plato became the first principle in the Middle Platonic philosophers Alcinous and Philo, in whom, under Aristotelian influence, the concept of divine simplicity incorporated notions of indivisibility, immutability, and incorporeality. Philo's Platonism combined with biblical faith provides the bridge to the study of Irenaeus in Chapter 3, who used ideas about divine simplicity to attack Valentinian ideas about divine emission, adding concepts of inseparability, consubstantiality, and contemporaneity that would be required for divine simplicity to be compatible with any process of generation. This claim sets up the struggles of the late second and third centuries Ip discusses in Chapter 4, when theologians had to confront the Monarchian theologies that could not account for the distinction between Father and Son, a problem that emerged in the prosopological exegesis of scripture. Ip argues that Tertullian was the first to exhibit any awareness of the potential conflict between divine simplicity and the scriptural distinction of Father and Son; it is in his writings that the fully trinitarian problematic becomes evident in Christian theology. Against the background of the foregoing chapters, chapter 5 examines how Origen synthesizes ideas of divine simplicity drawn from both philosophical and biblical sources, highlighting the Christian God's combination of metaphysical and ethical simplicity, which enables him to be both supreme first principle and the model of spiritual perfection for the Christian disciple. In chapters 6 and 7, Ip shows how ideas of divine simplicity enabled Origen to attempt a resolution of the trinitarian problematic. Chapter 6 examines how Origen upheld an anti-Monarchian/anti-psilanthropist distinction between Father and Son by attributing simplicity to the Father and multiplicity to the Son in view of his salvific involvement in creation and incarnation. One of the most interesting elements of Ip's analysis here is his survey of the various terms Monarchians rejected for the distinction between Father and Son (kat'hypostasin, idioteta, hypokeimenon, ousian), though he notes that the only term Origen unambiguously affirms to express that distinction is hypostasis. He also argues that Origen believes that the root of Christian monotheism lies in the status of the Father as the single source of divinity. Chapter 7 then looks at Origen's attempt to articulate the other side of the trinitarian problematic—how the Father and Son are unified as well as distinct. Ip suggests that in discussions of this topic, Origen responded to defenders of Valentinus, perhaps one Candidus, criticizing, as Irenaeus does, the notion of emissions as materialistic. Origen instead argued that the generation of the Son from the Father results in a hypostasis that is distinct but not separate from the Father if one conceives of that generation as an act of the Father's will emerging from his mind. Such a generation would be compatible with divine simplicity because no corporeal element would impede it. It would result in two hypostases and two wills, but wills united and harmonious, another protection for divine simplicity. Likewise, such a mode of generation would guarantee that the Son is the perfect image of the Father, and would have to be co-temporal and thus co-eternal with the Father. In a final epilogue, the author asserts that looking at Origen's theology in its third-century context would help scholars understand the transition from third- to fourth-century theology. He argues that the integration of anti-Monarchian and anti-Valentinian functions of divine simplicity that one sees in Origen breaks down with the emergence of Arius and the Nicene response, the discussion shifting from locating divine simplicity in the Father to locating it in the divine essence/ousia. He urges scholars to explore the possible reasons for that change.

This is a dense but well-organized and clearly written study. It is convincing in laying out the concerns of early Christian theologians who sought to balance philosophical notions of deity with scriptural revelation and its interpretation, as well as liturgical experience and the pursuit of exemplary discipleship—and to do this in the face of contemporary interpretations of Christian teaching they deemed deficient. It offers the scholar a foundation for the “prospective” examination of the evolution of the doctrine of the Trinity the author calls for instead of the “retrospective” consideration historians of doctrine often give to third-century authors like Tertullian and Origen, assessing these writers’ theology against the background of what became at the end of the fourth century Nicene orthodoxy. It further illuminates how Origen is the source for ideas on both sides of the fourth-century trinitarian debates, and is particularly relevant for understanding the context of the conflict between Eusebius of Caesarea, devoted student of Origen, and Marcellus of Ancyra, seen as the arch-Monarchian of the fourth century. This is an important study that historians of doctrine as well as scholars in systematic and philosophical theology will read with profit.