In two posts concerning my Damascene Ontological argument, it seems a lot of the controversy has surrounded what it means to “change.” The reason such a controversy erupted is my failure to adequately define “change” within the argument.
I would say that it might be better to use the terms “mutable” and “immutable,” which are more precise. To be mutable means to change in who we are or have within our nature to ability to increase or decrease in a certain property or function. For instance, a human can become wiser. A human can become more moral or less moral. Likewise, a human can be divided in the sense that he can reproduce himself (with the aid of another).
To be immutable means the opposite of mutable. It means to not be able to increase or decrease in property or function. It means one does not mature or become immature. One simply is. While an immutable being might have emotional reactions or change how his plans might come to fruition, it doesn’t follow that this constitues an actual “change;” nothing is added to the immutable entity, nothing is taken away. He stays the same, though his reactions might be different.
How do we apply this to the Incarnation? As was brought up in the comments, the idea that Christ could change in His human nature while remaining unchanged through His Divine nature appears to be a contradiction when we take Leibniz’s Law of Identity into accord. For those unfamiliar with the law, it basically says that for two things can be identical if they share the same properties. For instance, John the lawyer and John the father are the same person if they share the same properties. But, if John the lawyer has blond hair and is white while John the father has no hair and is black, they lack the same properties and therefore we cannot conclude they are identical (the logical formula for this is (x)(y)[(x = y)→ (P)(Px ↔ Py)]).
When we apply the Incarnation to Christ, we say that Christ (x) and God (y) are the same (x=y). So we look at a common property, such as immutability (P). We see that Christ changes (Px) and that God does not change (Py), therefore, we conclude that Christ is not God.
The problem with the structure of such an argument is that it fails to understand the Trinity. The premise that the Word has mutability as a property is based upon Arianism, which ascribed mutability to the Word and therefore taught that the Word was temporal and created.
The proper understanding of the Trinity is that Christ remained immutable in His essential nature, that is, His divine nature. Though divine, when He stepped into the human nature He allowed change to occur to His physical body. This does not mean God changed as the whole of the divine was not in the flesh, just the person of Christ. Thus, the Word remained immutable while changing in the flesh. This merely points out that Jesus remained God and man, thus sharing the same properties with God, but not always acting on them. This is a paradox, but not a contradiction.
Many Latin writers used the phrase “communicatio idiomatum” when referring to the Trinity, indicating a communication between the properties of both natures. As the linked article explains:
The source of the communicatio idiomatum is not to be found in the close moral union between Christ and God as maintained by the Nestorians, nor in Christ’s fullness of grace and supernatural gifts, nor, again, in the fact that the Word owns the humannature of Christ by right of creation. God the Father and the Holy Ghost have the same right and interest as the Son in allcreated things except in the human nature of Jesus Christ. This the Son by Assumption has made His own in a way that is not theirs, i.e., by the incommunicable property of personal union. In Christ there is one person with two natures, the human and the Divine. In ordinary language all the properties of a subject are predicated of its person; consequently the properties ofChrist’s two natures must be predicated of his one person, since they have only one subject of predication. He Who is the Word of God on account of His eternal generation is also the subject of human properties; and He Who is the man Christ on account of having assumed human nature is the subject of Divine attributes. Christ is God; God is man.
By having two natures, the Word remained God and retained His Divine nature, but also experienced what it was to be human. These two do not stand in contradiction to each other, but merely as two different experiences that Christ would have endured.