The motivations behind Apollinarius of Laodicea’s Christology are debated by scholars, but it is safe to say that from the beginning he opposed any sort of dualist Christology.1 In Antioch, in whose ecclesiastical affairs Apollinarius was involved since the early 360s, two presbyters connected with the pro-Nicene Meletian faction, Diodore and Flavian, espoused a dyophysite Christology.2 Diodore became bishop of Tarsus in 378 and Flavian bishop of Antioch in 381. It seems that it was not until the late 370s that Apollinarius came into conflict with them, over issues that were as much as ecclesio-political as Christological. Fragments of Apollinarius’s writings against Diodore and Flavian are preserved in three later polemical treatises: Theodoret of Cyrrhus’s Eranistes, Leontius of Byzantium’s Adversus Fraudes Apollinaristarum, and the Doctrina Patrum de Incarnatione Verbi. These treatises mention a number of different Apollinarian sources for the fragments they preserve, but it is unclear if they refer to a single tract by Apollinarius or several. At least one of Apollinarius’s writings against Diodore was addressed to a certain Herakleion who is otherwise unknown (Fragments 117–120). No more than titles are known about the others, however many there were.

Gregory the Great was the Roman pontiff from 590 until his death in 604. In the mid-570s he abandoned a successful career in government in order to become a monk. In 579 or 580 Pope Pelagius II ordained him a deacon and sent him to Constantinople as the papal ambassador. He spent about six years in the imperial capital, where he became the center of a circle of monks and clerics who read the scriptures together. The lectures on the biblical book of Job that he delivered in this setting he later revised for publication as the Moralia in Job, his most famous work and a treasure-house of moral, spiritual, and theological insight. Upon his return to Rome he resumed his monastic life, but was elected pope after the death of Pelagius II in 590.

The date of this text written by Apollinarius of Laodicea (ca. 315–392) is difficult to determine with specificity.1 It should simply be placed in the late 360s or 370s. Here Apollinarius lays out his understanding of the communicatio idiomatum, a Latin phrase that refers to the transference of traits in the incarnate Christ. As Apollinarius presents it here, the communicatio idiomatum permits a theologian to both observe and speak of the divinity sharing in the body’s characteristics and the body sharing in the divinity’s characteristics with respect to the incarnate Christ. Apollinarius notes that the conjunction of the two natures in Christ (see 4 below) results in a single, fundamental, undivided, and indivisible union between what is “same-in-substance” with God and what is “same-in-substance” with humanity. This “double consubstantiality,” as it is called – that is, Christ is homoousios with God and homoousios with humanity – is the Christological mechanism, so to speak, that allows for each nature to share in the qualities of the other without the philosophical or theological implications of sharing.

Theodore was a native of Antioch where he was trained in rhetoric by Libanius before entering the ascetical school led by Diodore (later bishop of Tarsus). He was ordained a priest by Flavian of Antioch in 383 and then in 392 was consecrated bishop of Mopsuestia. In the course of his long episcopal tenure Theodore came to be regarded as one of the foremost theologians and exegetes of the pro-Nicene cause. In addition to numerous biblical commentaries on books of the Old and New Testaments, he produced a set of catechetical homilies explaining the Nicene Creed and the Lord’s Prayer, polemical treatises such as Against Eunomius and Dispute with the Macedonians, as well as other works. Theodore’s On the Incarnation was also polemical, according to the late fifth-century Gennadius of Marseilles: