Hence, to allow one of the two while forbidding the other is a contradiction.

Addressing the Melkites, one may say:
“You claim that the divine nature united with the human nature at the very moment of conception, and that he was the Messiah even while being slapped, crucified, dead, and suffering. Yet you also add that all of this befell him only in respect of the human nature, not the divine. This inconsistency is of the same kind as the Nestorians’ inconsistency.”

Ibn al-Biṭrīq goes on to say:
“One should also ask the Nestorians: When did the Word unite with the man—before the birth, or at the very moment of birth?

If they answer, ‘before the birth,’ we ask them: Before the birth—meaning before conception, or before the birth while he was still in the womb?

Should they reply, ‘before the birth and before conception,’ they are in effect asserting that the union took place before he was a human being at all and before he was even formed. If that were so, the Nestorian claim that the Eternal united with a particular human being would collapse, because a particular human being does not come into existence until he is actually fashioned in human form."

It may therefore be said to him: This question presses upon all three sects alike, for they all posit a union even more sweeping than the one posited by the Nestorians.

And if it is objected, ‘They say that he united with a universal human,’ this is among the most unsound of claims; for the Messiah is a specific, individual human being, and the very concept of his individuality rules out any sharing in that identity—he was not some universal human.