[With The Cappadocians,]
the term hypostasis was dissociated from that of ousia
and became identified with that of prosopon.
But this latter term is relational,
and was so when adopted in trinitarian theology.
This meant that from now on
a relational term entered into ontology and, conversely,
that an ontological category such as hypostasis
entered the relational categories of existence.
To be and to be in relation becomes identical.
For someone or something to be,
two things are simultaneously needed:
being itself (hypostasis)
and being in relation (i.e. being a person).
It is only in relationship
that identity appears as having an ontological significance,
and if any relationship did not imply such an ontological meaningful identity,
then it would be no relationship.
Struck by parallels between this and many passages in I And Thou, by Martin Buber.