In my last post I showed how we must understand the doctrine of the Incarnation--Jesus Christ, one person in two natures--beginning with grammar rather than a metaphysical explanation that attempts to figure out in abstraction from the text how Christ's two natures 'compose' his one person. This is to put the cart before the horse. In the process, I explained how this wards off the potential rationalist objection that the distinction between person and nature is nonsense. When you start with grammar, a "person" isn't a fancy concept, but simply the subject of predication. And the two "natures," again, are simply referred to by different kinds of predicates. Jesus, for instance, has verbs predicated of him that stand for two different kinds of action: human and divine.
We could very quickly be drawn back into metaphysical conundrums, however, if we start to think about what it means to say that there are two different kinds of acts that Jesus does, that is to say, if we take the word "act" in an overly simplistic way. Dogs and people have different kinds of acts. One wags its tail and the other reads books. Yet the difference in kind isn't extreme enough to be a useful analogy between the divine and human nature's in Christ. What would a person look like who was fully human and fully canine? Would he have a human brain with a dog tail? You can see why it is easy to slide into a faulty compositional approach in our doctrine of the Incarnation.
The difference in kind between divinity and humanity has to be much more radical, which is, of course, the case given that God is Being (the "I Am" of Exodus 3:14) and all created things are beings. We use the word "being" analogously of both divinity and humanity, whereas we use the word "being" in exactly the same way of both humans and canines. This is because all creatures have their being derivatively and are dependent on God who has being necessarily. All created things have the same kind of "being." Analogy doesn't just apply to "being" either. It applies to all those other characteristics of God that might also apply to creatures: wisdom, goodness, truthfulness, holiness, etc.. For our purposes I want to explicitly point to the fact that the two-fold "action" (energeia in Greek) attributed to Jesus in the Bible is also merely analogous. That means that the "natures" that these actions manifest are merely analogous; they operate on different levels of being. The implication is that because our words do not apply in the same way to both natures, we should have no problem affirming the fullness of both natures. Just because one of Jesus' natures acts, it does not mean that the other one has to stop acting (Nestorianism). This means there is no 'compositional' problem to sort out. John Wyclif's rule of thumb for interpreting apparent contradictions in Scripture holds here: where there is equivocation (analogy), there is no contradiction. When we find two apparently contradictory things asserted (that Christ is fully human and divine), we must pay attention to how we are using language to see if we are speaking analogically. In this case the fullness of one implies no competition with the fullness of the other since they are on entirely different planes of being rather than on a single continuous plane of being (like humans, animals, angels).