Richard Muller on Communicatio Idiomatum

Communicatio idiomatum/ communicatio proprietatum: communication of proper qualities; a term used in Christology to describe the way in which the properties, or idiomata, of each nature are communicated to or interchanged in the unity of the person. The communicatio can be characterized as either in concreto or in abstracto (q.v.). The former qualification, in concreto, refers to the concretion of Christ’s person in the incarnation and personal union; the two natures are here considered as joined in the person, and the interchange of attributes is understood as taking place at the level of the person and not between the natures. This view was typical of the Antiochene Christology and of the Reformed Christology in the sixteenth and seventeenth centuries. The latter qualification, in abstracto, refers to the abstractive consideration of the relation of the two natures to each other distinct from their union in the person and to the exchange of properties between the natures, specifically, a communication of divine properties to the human nature.This view was typical of Alexandrian and Cappadocian Christology in the early church. Both views raise doctrinal problems: the Antiochene position, taken to an extreme by Nestorius, threatens the unity of Christ’s person; the Alexandrian doctrine, taken to an extreme by Eutyches, threatens the integrity of the natures. In addition, the logic of predication argues the illegitimacy of the use of abstractions as predicates. …

… (1) The genus idiomaticum, or idiomatic genus, indicates the predication of the qualities or attributes of both natures of the person of the Mediator, so that the God-man can be said, as one person, to suffer and die but also to govern and sustain the whole creation. The qualities of each nature (idiomata) belong to the person of Christ, but each nature retains its own idiomata, so that the qualities of one nature do not, according to the genus idiomaticum, become the qualities of the other. …

… we note that the Reformed view of the communicatio, which tend to be restricted to the genus idiomaticum, approaches the communication more as a praedicatio verbalis, or verbal predication, of idiomata from both natures of the person, whereas the Lutheran view insists that the person actually bears the idiomata of both natures. The Reformed, in addition, do not view the apostelesmata, or shared operations, of the natures as a genus of the communicatio idiomatum but as a separate communicatio apostelesmatum according to which the divine operations of both natures are brought to completion in the one work of Christ. Thus, the Lutheran teaching is a real communicatio while the Reformed, remaining at the level of a communicatio in concreto only, is quite accurately called antidosis onomatōn (ἀντίδοσις ὀνομάτων), a mutual interchange or reciprocation of names, rather than a transfer or communication of properties, … is… praedicatio vera, a true predication of attributes, but of the person only and not between the natures.

[Richard A. Muller, Dictionary of Latin and Greek Theological Terms: Drawn Principally from Protestant Scholastic Theology (Grand Rapids, MI: Baker, 1985), 72-4]