Mary is the Mother of Jesus.
Jesus is God.
Therefore, Mary is the Mother of God.
If you deny that Mary is the Mother of God, then you deny that Jesus is God.
Jesus is God.
Therefore, Mary is the Mother of God.
When a word or words change meaning in the usage of an argument the result is the fallacy of equivocation. The problem with the syllogism above is the ambiguity in the meaning of the words, "God" and "mother".
It's like saying:
Jesus is God.
God is a Trinity.
Jesus is the Trinity.
Cordially,
God existed before Mary did, so how can she be his mother?
To give birth to a god, one might reasonably expect the mother to be a god. Is Mary a god?