This ties in with my recent reflections on universals, natures, and metaphysics. This is from John McGuckin’s fine work on St Cyril. I applaud Perry Robinson for doing the legwork in putting these quotes on his blog:
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.”
7. “Ousia is the genus of a thing. Once can think, for example of the genus ‘unicorn.’ Such a genus exists, but only theoretically, not practically or concretely. It does not exist, that is, ‘in reality’ as we would say today. Nonetheless, it makes sense to talk of the necessary characteristics of a unicorn such as its magical horn, its horse like appearance, its whiteness, its beard and lion’s tail, and so on. Thus the genus of unicorn is the ousia, that which makes up the essential being of a thing.. The notion of the physis of our unicorn is intimately related to this. It connotes what we might call the palpable and ‘physical’ characteristics of a unicorn such as outlined above-but always understanding that his possession of a physis-nature still does not necessarily imply that such a creature is real…In some circles, especially those represented by the Christian thinkers of Alexandria following Athanasius, the word physis signified something slightly different from this sense of ’physical attributes’ and had been used to connote the physical existent-in the sense of a concrete individual reality. In the hands of Cyril the word is used in two senses, one in what might be called the standard ‘physical usage where it connotes the constituent elements of a thing, and the other in which it serves to delineate the notion of individual existent-or in other words individual subject. This variability in the use of a key term on Cyril’s part goes some way to explaining Nestorius’ difficulties in following his argument over the single Physis of the Incarnate Word (Mia Physis tou Theou Logou Sesarkoene). By this Cyril meant the one concrete individual subject of the Incarnated Word. Whereas Nestorius heard him to mean the one physical composite of the Word (in the sense of an Apollinarist mixture of fusion of the respective attributes of the natures of man and God.)
“The prospon is the external aspect or form of a physis as it can be manifested to external observation and scrutiny. It is a very concrete, empirical word, connoting what appears to outside observation. Each essence (ousia) is characterized by its proper nature (physis), everything that is, which makes it up, and in turn every nature that is hypostatically real presents itself to the scrutiny of the senses in its own prosopon-that list of detailed characteristics or ‘propria’ that constitute this thing individually and signal to the observer what nature (physis) it has and thus to what genus (ousia) it belongs. In the system Nestorius is following, every nature has its own prosopon, that such of proper characteristics (idiomata) by which it is characterized in its unique individuality and made known to others as such. The word carried with it an intrinsic sense of ‘making known’ and appeared to Nestorius particularly apt in the revelatory context of discussing the incarnation.”