Both the unity of the divine essence and the distinction of the persons within that essence are matters of ontology, of the divine being. Some, like Wollebius, define the divine persons as “the essence of God, with a certain manner of subsisting” (Christianae theologiae compendium 20-21). Modes of subsistence, therefore, are not functional relations at all. They are subsistent relations in the divine nature: the Father is relative to the Son as unbegotten, and the Son is relative to the Father as begotten. Functional categories cannot be introduced into the modes of subsistence without simultaneously redefining the classical doctrines of divine simplicity, actuality, unity, omnipotence, immutability, impassibility, and the like. If the Father and the Son “function in an eternal Father-Son relationship, in which the Father always acts in a way that befits who he is as Father, and Son always acts in a way that befits who he is as Son,” does that not require some kind of change in the Godhead? If immutability is redefined only as constancy then Ware may be able to avoid incoherence, but on the terms of classical theism, the introduction of function into modes of subsistence ad intra is no small problem (emphasis added—rsc).