Prosopon (,; from Ancient Greek: ; plural: Ancient Greek: ? prosopa) is a technical term encountered in Christian theology. It is most often translated as "person", and as such is sometimes confused with hypostasis, which is sometimes also translated as "person." Prosopon originally meant "face" or "mask" and derives from Greek theatre, in which actors on a stage wore masks to reveal their character and emotional state to the audience. Both prosopon and hypostasis played central roles in the development of theology about the Trinity and about Jesus Christ (Christology) in the debates of the fourth through seventh centuries.
The term "prosopon" is used for "the self-manifestation of an individual" that can be extended by means of other things. For example, a painter includes his brush within his own prosopon. (Grillmeier, 126)
St. Paul uses the term when speaking of his direct apprehension in the heart of the Face (prosopon) of Christ (II Cor 4:6).
Prosopon is the form in which hypostasis appears. Every hypostasis has its own proper prosopon: face or countenance. It gives expression to the reality of the hypostasis with its powers and characteristics. (Grillmeier, 431)
Two distinct Antiochene Christologists, Theodore of Mopsuestia, followed by his disciple Nestorius, supported the prosopic union of the two natures (physes) of Jesus Christ rather than the accepted hypostatic union.
Theodore of Mopsuestia maintained a vision of Christ that saw a prosopic union of the divine and human. This was a union where Jesus was only a man indissolubly united to God through the permanent indwelling of the Logos. (Grillmeir, 428-39) He believed the incarnation of Jesus represents an indwelling of the spirit of God that is separate from the indwelling experienced by the Old Testament prophets or New Testament apostles. Jesus was viewed as a human being who shared the divine sonship of the Logos; the Logos united himself to Jesus from the moment of Jesus' conception. After the resurrection, the human Jesus and the Logos reveal that they have always been one prosopon. (Norris, 25)
Theodore addresses the prosopic union in applying prosopon to Christ. He accounts for two expressions of Christ - human and divine. Yet, he does not mean Christ achieved a unity of the two expressions through the formation of a third prosopon, but that one prosopon is produced by the Logos giving his own countenance to the assured man. (Grillmeier, 432) He interprets the unity of God and man in Christ along the lines of the body-soul unity. Prosopon plays a special part in his interpretation of Christ. He rejected the Hypostasis concept - believing it to be a contradiction of Christ's true nature. He espoused that, in Christ, both body and soul had to be assumed. Christ assumed a soul and by the grace of God brought it to immutability and to a full dominion over the sufferings of the body. (Grillmeier, 424-27)
Nestorius furthered Theodore's belief in the prosopic union as thus: "prosopon is the appearance of the ousia: the prosopon makes known the ousia." The two prosopa are united "In Christ... the one prosopon does not belong to a nature or hypostasis which arose through the natural union of Godhead and manhood, but to the unity of the two unconfused natures." (Grillmeier, 510)
Nestorian notion of "two persons" (prosopic duality) caused heated debates among Christian theologians in the first half of the 5th century, resulting in official condemnation of such views. The Third Ecumenical Council (431) affirmed the teaching of "One Person" of Jesus Christ, condemning all other teachings. The Fourth Ecumenical Council (451) reaffirmed the notion of One Person of Jesus Christ, formulating the famous Chalcedonian Definition with its "monoprosopic" (having one person) clauses, and in the same time explicitly denying the validity of "dyoprosopic" (having two persons) views.