“This formulation of divine simplicity has proceeded on the conviction that this attribute is an implicate of God’s singularity, aseity, immutability, infinity, and act of creatio ex nihilo.
It has been maintained throughout that a dogmatic approach to the doctrine is in order, and this has involved attending to the biblical teaching on the various attributes that imply God’s simplicity and supplying elaborative clarification and examining the ways in which each of these divine perfections conduct the theologian to a recognition of simplicity.
After delineating the central claims of the doctrine of divine simplicity, the proposed exegetico-dogmatic approach was carried out, following the manner in which each of the attributes distinctly considered addresses and vouchsafes certain of the constituent claims of the teaching of God’s simplicity.
God’s singularity implies that He is Himself the fullness of His deity subsisting, that He transcends the categories of genus and species, that He is really identical with each of His perfections and is therefore not composed of substance and accidents, and that He is without composition altogether in the uniqueness with which He is God.
God’s aseity implies that He is actus purus, ipsa deitas subsistens, ipsum esse subsistens, really identical with each of His own perfections, and free from all composition with nothing back of Him governing or actualizing His being.
Likewise, God’s immutability implies again that He is wholly in act, without potentia passiva whereby He might be altered or enhanced.
In His selfsameness and indivisibility, He is each of His perfections subsisting, without accidents and without any composition whatsoever.
God’s infinity too implies that He is actus purus. In His boundless perfection, each of God’s attributes is really identical with His essence, and each of the divine persons is really identical with His essence subsisting in a certain manner.
Finally, the act of creatio ex nihilo implies that God is actus purus and ipsum esse subsistens without any eternal co-existents.
Just so, the simple triune Creator is the self-efficacious and ultimate origin of all that exists.”
–Steven J. Duby, Divine Simplicity: A Dogmatic Account (T&T Clark Studies in Systematic Theology; New York: Bloomsbury Academic, 2018), 235.