In his wise, wide-ranging contribution to Recent Developments in Trinitarian Theology, Christoph Schwobel argues that trinitarian theology necessitates a revision of metaphysical assumptions.
“It is,” he writes, “one of the most significant discoveries of the classical disputes of trinitarian doctrine in the early church that the straightforward application of a received philosophical conceptuality to the doctrine of God leads into difficulties.” If the three are three substances sharing an attribute, we are heading toward tri-theism. If only one of the three Persons is fully divine, then we can protect the transcendence of God but “at the expense of having two demigods, all too familiar in the religious world of the Mediterranean in late antiquity.” Arianism misses the “astonishing demythologizing effect” of orthodoxy” (24). It became clear that the old metaphysics simply could not do.
And at least the initial shape of the alternative metaphysics came into view: “Even such a simplified picture of some of the problems confronting trinitarian reflection can quickly demonstrate that trinitarian theology must in some sense engage in revisionary metaphysics and that for this kind of metaphysics the category of relation has paramount importance” (24). As Schwobel points out, the “classical terminology of ‘unbegotten,’ ‘begotten,’ and ‘proceeds’ clearly names relations” (24).
The inner-trinitarian relations “are in a sense mutually constitutive and reciprocal, though asymmetrical relations”; these relations are what make the Father Father, the Son Son and the Spirit Spirit. Thus there is in God “a real otherness” but because this difference is constituted by the three in relation the three “also constitute, because they are constitutive relations, a real togetherness” (25).
Trinitarian theology not only forces a revision in theology proper - in “divine metaphysics” - but in our understanding of creation: “The relations of the Trinity to the world are constitutive for the being of the world but not for the being of God.” Yet, the fact that the Creator is this relational God must have an effect on the way the world goes: “when this relational God relates to what is not God in creation, reconciliation, and eschatological consummation, God relates in such a way that God creates a relational world, a world of created particularities and created forms of togetherness” (25).