Divine simplicity in the theology of Irenaeus

Scholars have examined early Christian appropriations of the philosophical language of divine simplicity, but there is no extended study focused specifically on Irenaeus, even though he provides the earliest extant Christian explanation of the concept. This thesis argues that Irenaeus develops a rich account of divine simplicity that is intrinsically related to several other more well-known aspects of his thought. This account emerges from a complex appropriation and development of philosophical ideas, biblical exegesis, and diverse discussions of divine simplicity among contemporary Christians.

In Part 1, the thesis focuses on Irenaeus’ definition of divine simplicity (haer. 2.13). The account of God provided by the rule of truth is clarified by the claim that God is simple. Specifically, this concept of divine simplicity sets parameters on appropriate statements about God in se and God’s relationship to creation. In Part 2, the thesis explores the implications of divine simplicity for Irenaeus’ wider thought, focusing especially on how divine simplicity affects his theology and scriptural interpretation in later books of Against Heresies when discussing divine will, generation, activity, and power.

For Irenaeus, the concept of divine simplicity involves the fundamental principle that God’s will, activity, names, and powers cannot be understood separately, but should instead be thought of as mutually entailing, because God, unlike humans, is not composite. By “mutually entailing” I mean that God’s names and powers imply one another without being identical, since they are distinct in unity. Because God is simple, language about humans cannot be applied univocally to God, and instead, God is understood as self-similar. Irenaeus’ account of divine simplicity provides an important insight into second-century theology and should be viewed as a significant development in the history of the concept in early Christian thought.