What a fool can understand, anyone can understand, fools being, by definition, deficient in candle power and wisdom. Why should we suppose, then, that a being than which none greater can be conceived by the fool is as great as a being than which none greater can be conceived, say, by a smart Philosophy Now reader? And by the same reasoning, why should we suppose that a being than which none greater can be conceived by you, with all due respect, is as great as a being than which none greater can be conceived by a genius like Einstein or a saint like Anselm? Finally, why should we suppose that a being than which none greater can be conceived by Einstein or Anselm is as great as a being than which none greater can logically possibly be conceived – than which none greater could be conceived even by God? For plainly this, and not merely the greatest concept of which the fool is capable, is what Anselm’s argument requires.
To see why this clearly misconceives the argument, notice that the phrase "a being than which none greater can be conceived by the fool" is an ambiguous expression. It can mean either:
a being than which a fool cannot conceive a greater
a being than which none greater can be conceived, as understood by a fool.
The latter poses no problem for Anselm. Anselm is quite willing to admit that we can have degrees of understanding of "that than which nothing greater can be conceived"; in fact, as he himself notes, this possibility follows directly from the description, since that than which nothing greater can be conceived is conceived to be greater than anything that can explicitly be thought by us. Contrary to Carey's claim, it is Anselm, not Gaunilo, who is closer to the apophatic tradition. While I don't agree with everything he says, Jean-Luc Marion has done some interesting work in showing just how apophatic one's interpretation of the argument can get before one breaks it. The former, however, is the way in which Carey takes it, and it clearly will not do: it is not equivalent to "that than which nothing greater can be conceived."
Carey also misinterprets Aquinas's objection. Aquinas makes a distinction between what is self-evident in itself and what is self-evident to us. God's existence is self-evident in itself (God can recognize its self-evidence) but not self-evident to us. Carey seems not to have grasped the reason for saying the former, however. On Aquinas's view we can prove that God's essence includes his existence. This means that in principle it is possible to recognize that God exists simply from direct knowledge of what God is. Now this sort of knowledge would be available to God. It is not available to us, however, because our knowledge of the divine essence is indirect, consisting largely of what it is not and how it is related to other things. Therefore we can't recognize its self-evidence directly, although we can prove that it would be self-evident to someone under particular conditions. There is nothing puzzling or mysterious about this.