From Ott's Fundamentals of Catholic Dogma:

The ontological basis of the communication of idioms is the community and mutual communication of the Divine and human properties and activities in Christ. This derives from the unity of the Person in such fashion that the human properties are predicated of the Word and the Divine properties of the Man-Christ. The communicatio idiomatum in the logical sense (predication of idioms) obviously derives from the ontological reality.

Christ's Divine and Human characteristics and activities are to be predicated of the one Word Incarnate. (De fide)

And later, about the "Rules Concerning the Predication of Idioms":

The nature of the Hypostatic Union is such that while on the one hand things pertaining to both the Divine and the human nature can be attributed to the person of Christ, on the other hand things specifically belonging to one nature cannot be predicated of the other nature. Since concrete terms (God, Son of God, Man, Son of Man, Christ the Almighty) designate the Hypostasis and abstract terms (Godhead, humanity, omnipotence) the nature, the following rule may be laid down: communicatio idiomatum fit in concreto, non in abstracto. The communication of idioms is valid for concrete terms not for abstract ones. So, for example: The Son of Man died on the Cross; Jesus created the world. The rule is not valid if there be reduplication, [and if] by reduplication the concrete term is limited to one nature. Thus it is false to say "Christ has suffered as God," "Christ created the world as a human being." It must also be observed that the essential parts of the human nature, body and soul, are referred to the nature, whose parts they are. Thus it is false to say: "Christ's soul is omniscient," "Christ's body is ubiquitous."

Further, predication of idioms is valid in positive statements not in negative ones, as nothing may be denied to Christ which belongs to Him according to either nature. One, therefore, may not say: "The Son of God has not suffered," "Jesus is not Almighty." Assertions liable to be misunderstood should be protected by clarifying additions like "as God," "as man," for example, "Christ, as man, is a creature."

Interesting stuff, in my opinion.