Jesus is a carpenter.
Mary is the mother of Jesus.
Therefore, Mary is the mother of a carpenter.
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Jesus is God, the Second Person of the Trinity.
Mary is the mother of Jesus.
Therefore, Mary is the mother of God, the Second Person of the Trinity.
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Two questions:
Is the first syllogism formally valid or invalid?
Is the second syllogism formally valid or invalid?
I'm not sure what's so hard for Catholics to understand about that.