Anselm of Canterbury (1033 – 1109) was a medieval theologian. According to Anselm's ontological argument for the existence of God, "accidental beings" are all those things -- essentially all sense objects -- whose non-existence could be imagined without inherent contradiction, and "necessary beings" are those things whose existence is guaranteed precisely by what they are. Because accidental beings could not have guaranteed that they ever would come into existence, there must be a necessary being upon whom all the accidental beings depends to bring them into existence; and this necessary being Anselm identifies with God, who therefore clearly must exist.
In our modern analysis, this eleventh century argument is most vulnerable to what criticism?