In his Systematic Theology: Volume 1, The Triune God, Robert Jenson critiques the Augustinian legacy in Western theology that tends to flatten out the differences between the respective agencies of the persons of the godhead. For Augustine, Jenson says, “there is no difference at all between the agencies of Father, Son, and Spirit. Either, he thinks, Father, Son, and Spirit must simply do the same thing, or simply different things” (and Augustine rejects the latter) (111). One of the most “disastrous” applications of this principle, in Jenson’s view, was Augustine’s teaching (in the words of Peter Lombard) that “As the Son was made man, so the Father or the Holy Spirit could have been and could be now” (Sent. 3.1.3). If the agency among the divine persons, in other words, is univocal among them, then it stands to reason that the act of incarnation cannot be proper or unique to any one of the persons, but must be shared by each. Against this view Jenson pits the “authentically Nicene analysis” of John of Damascus, who wrote that “It was the Son of God who became the son of man, so that his individuating property might be preserved. As he is Son of God he became a son of man…” (Expositio fidei 77.5-8). As Jenson summarizes the problem with the Augustinian position, the
supposition that there is no necessary connection between what differentiates the triune identities in God and the structure of God’s work in time bankrupts the doctrine of Trinity cognitively, for it detaches language about the triune identities from the only thing that made such language meaningful in the first place: the biblical narrative. (112)
My response: the conflict might also be viewed in terms of the theistic possibilism-actualism debate I have been developing here of late. On the Augustinian view, the “possibility of Incarnation” seems at some risk of becoming an abstract, uncreated possibility simply given to or for God, not simply as Creator, but now more specifically as a Trinity of divine persons. According to the doctrine of divine ideas, God’s will ranges over all the possibilities that are his with respect to creation. On the Augustinian view of the univocal agency of the divine persons, the classic Augustinian voluntarism and possibilism receive an even further, deeper, more problematic application, as the divine will is here allowed to range over possibilities that reference not only created being per se, but also how the persons of the Trinity in particular may (or may not) relate to that created being. (Consistent with this position is the later “personal properties” debate of the high and late Middle Ages, which was waged over whether it was the property of relation (the Dominican position) or the property of emanation (the Franciscan position) that was primarily responsible for constituting the persons in their distinct personhood. Either way, this is to posit a prior ontic framework that afterward makes the Trinitarian persons “possible.”)
As for the Damascene position tying the possibility of Incarnation to the Son only, while this conclusion could be drawn as the result of an even more limiting possibilism (i.e., the possibilities for Incarnation are still viewed as prior to and determinative of all Trinitarian action, as per the Augustinian position, it’s just that the range of available options have now been narrowed from three to one), the thrust of Jenson’s discussion, as I understand him, would seem to be to see the divine Son simply as God’s own possibility of Incarnation. If the Father or the Spirit are able to become Incarnate, the Son is that possibility for them. The possibility of Incarnation is not, accordingly, something that precedes or co-exists eternally with the persons of the Trinity, distinguishing them (or not, as the case may be) from each other; rather it is the prior actuality and givenness (and giftedness) of the divine persons for each other that afterwards determines the character of the possibility of their givenness for creation.