The following is an excerpt from STR Enhanced Solid Ground July 2012 by Greg Koukl. 

  • "Either Jesus is not God or God is not a trinity. "

This is a failure of equivocation, but the problem is difficult for most to see at first. It has to do with the troublesome word, “is.” There are at least five meanings for the word “is.”

Resolving the equivocation in this argument requires distinguishing between the “is” of essential predication (“Aristotle is human”) and the “is” of identity (“Aristotle is the author of the Nichomachean Ethics”). There are also the parts/whole “is” (“Aristotle is skin and bones”), the “is” of accidental predication (“Aristotle is white”), and the “is” of existence (“Aristotle is”). 

When Christianity teaches that Jesus is God, it doesn’t mean that Jesus and God are exactly identical. Jesus is different from the Father. He shares the Father’s essential nature, but He is not everything that God is. God subsists in three persons; Jesus is only one of those persons.

  • “Jesus is God. Mary is the mother of Jesus. Therefore, Mary is the mother of God.”

The form here seems correct—the conclusion follows from the premises. It also seems that the individual statements are true. But something’s wrong here. God is not the kind of being that has a mother. Where did we go wrong?

The problem becomes more obvious when we take it a step further: “Mary is the mother of God. God is a trinity. Therefore, Mary is the mother of the Trinity.” This, of course, is patently false. But why is there a problem if the form is sound and the claims are in order?

The trouble lies with the terms. There’s an equivocation here on the clause “Jesus is God” in the first syllogism. Jesus is a very unusual individual. Yes, He is God, but He’s also fully human. Jesus is one person with two natures, the nature of God and the nature of man.

When we say Jesus is God, we are not saying His humanity is divine. That would be a contradiction. We are saying He is God in that He has a divine nature. Mary is the mother Jesus in the sense that she’s the mother of His humanity. She is the mother
of His human nature, not His divine nature.

Equivocation—lack of clarity—on these terms makes a false conclusion seem sound. The claims are right. The form is right. But the conclusion is false because the meanings of the terms are equivocal.

Page 5 of STR's July 2012 issue of Solid Ground - 

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