Divine Logic

Catholics are very familiar with addressing the Blessed Virgin Mary as "Mother of God," just as we do in the Haily Mary: "Holy Mary, Mother of God, pray for us sinners." This is an ancient title for Mary, which was officially approved and sanctioned by the Church at the third Ecumenical Council, at Ephesus, in 431 AD. Some people objected to it then because they had a distorted view of the nature of Christ, but this should be an easy one, right? It's simple logic:

Jesus is God.
Mary is the mother of Jesus.
Therefore, Mary is the mother of God.

But did you know that some Evangelical Christians object to this title today? They say it gives Mary too much honor to be called the Mother of God--to that I would respond, "If the shoe fits, wear it." I also heard one Evangelical in a debate try to show that calling Mary the Mother of God is absurd by making this counter-argument:

God is Trinity.
Mary is the mother of God.
Therefore, Mary is the mother of the Trinity.

"But this is absurd! No Christian believes Mary is the mother of the Trinity! See, Catholic, your logic is flawed!"

Indeed it is absurd, 'cause your logic is flawed.

There are two problems here. One is a formal problem, which may be a little complex to get into here (i.e. I'm not sure I understand it well enough to explain it), but suffice it to say that the way that syllogism is set up renders it invalid. I think it can be demonstrated with another example:

God is Trinity.
The Father is God.
Therefore, the Father is Trinity.

Well, that didn't work, did it? So the first issue is the form of the argument.

The other problem is called the fallacy of four terms. This is when a logical proposition uses one word in two different ways, so that the word does not mean the same thing every time it is used. Here is a handy example (borrowed from the Wikipedia page on the subject of this fallacy):

Major premise: Nothing is better than eternal happiness.

Minor premise: A ham sandwich is better than nothing.

Conclusion: A ham sandwich is better than eternal happiness.

The word "nothing" in the example above has two meanings, as presented: "nothing is better" means the thing being named has the highest value possible; "better than nothing" only means that the thing being described has some value. Therefore, "nothing" acts as two different words in this example, thus creating the fallacy of four terms.

Just as the word "nothing" is being used in to mean two different things in this example, so "God" is being used to mean two different things in the Evangelical example.

The three Persons of the Trinity are each fully God, so that it can properly be said of each, "The Father is God, the Son is God, the Spirit is God." We say that "God" can be predicated of each person of the Trinity, and everything that can be predicated of God-ness can be predicated of each of them, e.g. omnipotence, omnipresence, eternity, etc. Think of it like this: Nick is human. Jim is human. That means both possess human nature. Everything that can be said of human nature can be said of Nick and Jim: they are rational, they can see humor, etc. Just so, saying "The Father is God" and "The Son is God" means both possess the divine nature, and everything that can be said of the divine nature can be said of each of them: they are all-loving, all-just, all-merciful, etc.

BUT the process does not work in reverse: just because Nick and Jim share human nature, and just because the Father and the Son share divine nature, does not mean that everything that can be predicated of one can be predicated of the other. Though Nick and Jim share human nature, that does not mean that Nick is Jim. And though the Father and Son share divine nature, that does not mean the Father is the Son. The Father's fatherhood is unique to Him, and the Son's place as Son is unique to Him. Likewise, since it is only the Son that became incarnate in the Virgin's womb, only the Son can be said to have been born of her, and thus Mary is said to be Mother of God only as it relates to the Son.

No one should make the mistake of thinking that calling Mary "Mother of God" makes her the Mother of the entire Trinity, and no one should think that this title makes Mary superior or even equal to God. The title simply acknowledges that the one to whom Mary gave birth is truly the God, and that the God to whom Mary gave birth did truly become human. The only way you can deny the title Mother of God to Mary is to either deny that Jesus is truly human or that Jesus is truly God. And I don't think any who call themselves Christian would want to do that.