This thesis presents a case for the traditional doctrine of divine simplicity by construing it along the lines that God exists as actus purus. My formulation of divine simplicity draws upon the medieval insight that God is what He is in virtue of what He does in one, eternal act of will with which He is identical. In chapter I, I survey the contemporary literature on divine simplicity. In chapter II, I critique Alvin Plantinga??s Platonic theory of the divine attributes as formulated in Does God Have a Nature? I contend it brings with it the cost of abandoning the doctrine of God??s aseity, as well as a problematic understanding of the very notion of what it means to claim that God has a particular property. In chapter III, I provide rejoinders to all of Plantinga??s defeaters against divine simplicity. I argue that by understanding the origin of God??s attributes to be the result of what He does, Plantinga??s two major criticisms against divine simplicity fail. In chapter IV, I develop a viable theory of divine simplicity, given an actus purus conception of God, and I formulate a number of arguments supporting it. By drawing upon the resources of action theory, I clarify, in detail, what exactly it means to claim that God is identical with His act of will. And I demonstrate the fruitfulness of an actus purus construal of divine simplicity by showing how it solves a large number of problems that theists face.In the last chapter, I note some of the difficulties with my position due to its commitment to an eternal God, and I suggest some of the ways that these problems can be overcome. However, in addition to showing the difficulties that face my position, I also demonstrate the rich number of implications that follow from it. As such, I seek to demonstrate that the traditional understanding of the divine essence is something that is worthy for theists to embrace and to explore, because it is full of truth and wisdom that deserves to be preserved for later generations to celebrate and enjoy.

This study traces the first steps of how divine simplicity entered into Christian Trinitarian discourse. It is the burden of this thesis to demonstrate that divine simplicity emerged in the ante-Nicene period with a distinctive status quaestionis concerning (a) the meaning of the doctrine, and (b) its function in reflections on the Father-Son relation. The first part argues that simplicity emerged in the ante-Nicene period with two possible trajectories of interpretation, anticipated by Plato’s Republic and Phaedo respectively. In the apologists, divine simplicity emerged as a purely metaphysical doctrine. However, a richer interpretation of the doctrine is also available in ante-Nicene theology, as exemplified in Origen’s understanding of divine simplicity as a metaphysical-ethical synthesis, meaning that (a) God’s nature is perfectly incorruptible, and (b) God’s character is perfectly free from contradictions. The second part argues that divine simplicity acquired a role in ante-Nicene reflections on the Father-Son relation within two significant ante-Nicene contexts: (a) polemic against Valentinian emanation (prolatio/probolē) and (b) polemic against Monarchianism. The genius of Origen is to utilise divine simplicity for avoiding the Monarchian identification between the Father and Son on the one hand, and the Valentinian separation between the Father and Son on the other. Consequently, we find the surprising conclusion that divine simplicity serves as a principle of differentiation as well as unity between the Father and Son. This thesis raises new questions for both modern theologians and patristic specialists. For modern theologians, the ante-Nicene developments suggest the Son’s generation as a fruitful site for further analysis on the relation between divine simplicity and Trinitarian theology. For patristic specialists, ante-Nicene developments highlight the need to account for the transition from the ante-Nicene to the post-Nicene status quaestionis: how did divine simplicity change from being attributed to the Father (ante-Nicene) to being attributed to the divine essence (post-Nicene)?

This thesis offers a constructive account of the doctrine of divine simplicity in Christian theology. In its methodology, the thesis aims to present this divine perfection as an implicate of the scriptural portrayal of God, to draw upon the insights and conceptual resources of Thomas Aquinas and various Reformed orthodox theologians, and to respond to some objections to divine simplicity. The focus on exegetical elaboration of biblical teaching and the use of Thomas and the Reformed orthodox distinguish this work from a number of recent accounts of God in both systematic theology and analytic philosophy. The case for God's simplicity is made by examining God's singularity, aseity, immutability, infinity, and act of creation in Holy Scripture and then tracing the ways in which these descriptions of God imply that he is (negatively) not composed of parts. Rather, he is (positively) actus purus and really identical with his own essence, existence, and attributes, each of which is identical with the whole being of the triune God considered under some aspect. In light of the constructive work, this study then addresses the three most pressing objections to divine simplicity: (1) that it denigrates God's revelation of his many attributes in the economy; (2) that it eliminates God's freedom in creating the world and acting in history; and (3) that it does not cohere with the doctrine of the Trinity.