Defining Jesus’ two natures and wills in one person begins with the Greek terms ouisa, hypostasis, and physis /prosopon. These terms took shape in the second century, with Justin Martyr, Tertullian, Irenaeus, and Origen first drawing distinctions between Jesus as the Son of Mary and Jesus as the Son of God (O’Collins 170, 173).
Based on the notion of communicatio idiomatum – that is, the interchange of properties / the distinction between Jesus as ‘Son of God’ and Jesus as ‘Son of Mary’ (O’Collins 173) — the second century Church Fathers and ecclesiastical writers began drawing connections from Jesus as Logos (Word) to the terms ouisa / Jesus as ‘essence’ or ‘substance’, and homoousios / Jesus is consubstantial with the Father (O’Collins 182).
Meanwhile, several splinter movements were also discussing the same terms, and a mess of “linguistic ambiguities and early intimations” (O’Collins 170) ensued over the next few centuries. Namely (and something akin to the “Who’s on First” skit by Abbott and Costello), the Catholic Church and the splinter movements engaged in mind-bending debates over how to apply the terms ouisa, homoousios, hypostasis, and prosopon to Jesus’s relationship with the Father, as well as to his divine and human natures during his earthly mission (O’Collins 178, 183).
Although several early Church Fathers contributed to the definitions established and then confirmed at four key Councils — Nicaea I, Constantinople I, Ephesus, and Chalcedon (O’Collins 198) — a few Church Fathers, in particular, laid the essential groundwork for correct definitions and trinitarian theology overall, which then helped the Church fully explain Jesus’ two natures and wills in one person.
For example, Tertullian defined God as one substance / ouisa in three distinct, yet not separate, persons; and that Jesus as the Word, as an incarnation, is two distinct substances in one ‘person’. In other words, the substances are not mixed (O’Collins 178, 179). Justin’s imagery about the consubstantial / homoousios relationship between Jesus and the Father complimented Tertullian’s work: As the Sun and its rays are of one substance yet distinct, so is the case with the Son and the Father (O’Collins 175).
Nicaea I built on the earlier Church Fathers’ contributions and confirmed similar definitions in the Creed: The Son is ‘of the ousia of the Father, the Son and Father (and Holy Spirit) are homoousios, yet all three hypostases (‘persons’) are distinct (O’Collins 182). Still, because ousia and hypostasis were often treated as synonyms, and striking the right balance of words meant avoiding extreme views (modalist versus pagan), Basil of Caesarea and Athanasius of Alexandria boiled down the various terms as follows: homoousios refers to the identical essence among three persons; the Father and Son are of the same ouisa (also referring to numerical identity; and each person has individual subsistences (hypostasis) within the ousia in God (O’Collins 185).
With ouisa and hypostasis having more solidified definitions, one remaining challenge was to tie together Jesus’ consubstantial relationship with the Father and his two natures in one person. Here, Cyril of Alexandria’s contributions explained how hypostasis, physeis (natures), and prosopon (person) could be applied to Jesus’ two natures. Cyril essentially upheld Nicaea’s pairing of ousia and hypostasis, while also adding physeis to describe Jesus’ two natures — one human, one divine — and prosopon to indicate one person holding both natures. Choosing prosopon over the plural (prosopa / persons) was largely based on Jesus’ natures being distinct, though within one person. Otherwise, and what was one of many flaws in Nestorious’ arguments for prosopa, Jesus would have also been two ‘sons’ (O’Collins 193, 194).
In short, and as the Council of Chalcedon confirmed, Jesus’ unity is based on one prosopon who did not have blended or ‘hybrid God’ kind of physeis. Rather, through his earthly birth, because of the Blessed Virgin Mary, Jesus’ human nature was formed. And because of his eternal pre-existence with the Father, he also had a divine nature (O’Collins 196). This conclusion would also reinforce Jesus’ double-consubstantiality / “divine with Father and human with his mother” and his double-generation / “perfect God and perfect man” (O’Collins 194, 195).
Works Cited
O’Collins, Gerald. Christology: A Biblical, Historical and Systematic Study of Jesus. 2nd ed., Oxford: Oxford University Press, 2009.