Aristotle makes an ontological distinction between substances and accidents. Significantly, Augustine develops his predicational view of divinity within a Platonic or Aristotelian metaphysical framework. For example, the bishop thinks substantia is virtually equivalent to the Latin essentia or Greek ousia (De Trinitate 5.2.3). God is uniquely "substance" (essentia) in that divinity does not exemplify any contingent or non-essential properties (= accidents). Almighty God just is his own wisdom, goodness, power, love or mercy (i.e. the "simplicity of God"). Divine simplicity means that God is neither composite nor mereologically constituted: there is no potentiality in God since deity possesses no parts (the divine one is actus purus). Being non-composite, God is not an entity constituted of form and matter. He is just pure form.
Of course, the teaching of God’s simplicity (simplicitas Dei) does not fail to encounter its own logical difficulties. Copan and Craig argue that it "seems patently false" to make the assertion that God does not have properties that are distinct from one another. The property of being good apparently is different from the property of being omniscient, just as the property of being omnipotent is not identical with the abstract property of being omnibenevolent. Moreover, Stead argues that it is problematic to argue that God’s action is "simple and uniform." For divine simplicity does not adequately explain how God loves many creatures or governs the multitudinous events occurring in the world; nor does it seem to preserve the notion of a God, who personally acts in the world of his creation. Defenders of this doctrine, however, contend that the supposed problematics associated with God's simplicity emanate from dissimilar ontological emphases between the medieval and modern periods, not from the concept of simplicity itself. The medieval thinkers stress constituent ontology, whereas moderns tend to emphasize relational ontology. Whether the difficulties of the doctrine are real or imagined, it seems certain that one encounters the simplicity of God doctrine in Augustine (Confessions 4.16.28).