Orthodox Christians are universally committed to the confession that God is absolute, but they are not always agreed on how to characterize this absoluteness. Historically the doctrine of divine simplicity has been regarded as indispensable for establishing the sufficient ontological condition for divine absoluteness. Accordingly, the Westminster Confession of Faith 2.1 confesses both that God is "without parts" and is "most absolute." But there no longer seems to be a broad consensus on the truth or usefulness of the doctrine of God's simplicity. Indeed, the doctrine has been criticized and dismissed by many recent Christian philosophers and theologians alike on the grounds that its supposed theological benefits can be preserved by less recondite doctrines. Moreover, many are convinced that the classical form of the doctrine is simply incoherent.

It is the contention of this study that to forfeit the doctrine of divine simplicity is to jettison the requisite ontological framework for divine absoluteness. The classical doctrine of simplicity, as espoused by both traditional Thomists and the Reformed scholastics, famously holds forth the maxim that there is nothing in God that is not God. If there were, that is, if God were not ontologically identical with all that is in him, then something other than God himself would be needed to account for his existence, essence, and attributes. But nothing that is not God can sufficiently account for God. He exists in all his perfection entirely in and through himself.

In order to understand the claims of simplicity the various models of physical, metaphysical, and logical composition that characterize non-divine things, and which demonstrate their ontological contingency, are examined. Simplicity denies that any of these varieties of composition can be applied to God without undermining his self- sufficient absoluteness. Furthermore, simplicity is shown to be a crucial element in many classical doctrines including divine aseity, unity, intinity, immutability, and eternality. In addition to considering the metaphysical and theological character of the doctrine, this study further argues that simplicity establishes the ontological absoluteness of God's existence, attributes, knowledge, and will and is thus necessary to maintaining a sufficiently strong Creator-creature distinction. The dissertation draws extensively on both Thomistic and Reformed sources.