Classical Metaphysics: Some Terminology

I mention classical metaphysics or substance ontology a lot. I suppose it's fair that I define my terms.  Bruce McCormack notes,

1. The order of knowing runs in the opposite direction to the order of being.   This means before we "know" God we are operating with some abstract notion of "being" or "person" and projecting that onto God. As McCormack argues, "The consequence of this methodological decision is that the way taken to the knowledge of God controls and determines the kind of God-concept one is able to generate" (187). This leads to:
2. Metaphysical thinking in "the strictest sense of the term."  We are beginning "from below" and through an inferential process determining what God can be.
3. Which means that we have a fully-formed (or mostly formed) concept of what God is before any consideration of his self-revelation in Christ.  As McCormack notes, "the content of Christology will be made to conform to a prior understanding of God" (188).  Natural theology has now given us a definition of God apart from God's decision to elect, save, create, etc.  There is now a metaphysical "gap" between God in the abstract and the Triune God.  

McCormack, Bruce.  "The Actuality of God: Karl Barth in Conversation with Open Theism." Engaging the Doctrine of God, ed. Bruce McCormack, Grand Rapids, MI: Baker, 2008.

We see this playing out with great confusion in the Nestorian debate.  John McGuckin writes,

Ousia: Essence, substance, being, genus, or nature.

Physis: Nature, make up of a thing. (In earlier Christian thought the concrete reality or existent.)

Hypostasis: The actual concrete reality of a thing, the underlying essence, (in earlier Christian thought the synonym of physis.)

Prosopon: The observable character, defining properties, manifestation of a reality.

Even at first sight it is clear that the words bear a range of meanings that overlap in some areas so as to be synonymous.  This is particularly so with the terms Physis and Hypostasis which in the fifth century simultaneously bore ancient Christian meanings and more modern applications.. In relation to Physis, Cyril tended to use the antique meaning, Nestorius the modern. In relation to Hypostasis the opposite was the case.”

True, both Cyril and Nestorius used the terms to different ends, but neither challenged the metaphysical grammar--and neither gave a satisfactory solution.

John Anthony McGuckin, St. Cyril of Alexandria and the Christological Controversy, SVS, 2004,