[1] Previously I pointed out an equivocation in the Island objection to Anselm's argument; if the key description is taken in a way that actually parallels Anselm's, it is obviously problematic in a way that Anselm's is not. The alternative interpretation (C), which is how everyone thinks of it, is not parallel. Given that the Island objection crucially depends on being parallel to Anselm's argument (that is how it performs its reductio), the Island objection equivocates in a key place.
(C) that island than which no greater island can be thought
(C) is not parallel to (A), and the Island objection cannot succeed unless it manages a parallel in all relevant aspects.
[2] But even if this is set aside, it immediately involves an additional problem. As Anselm pointed out in his reply to Gaunilo, the key point in (A) is that we are talking about something than which nothing greater can be thought, not simply something greater in some way. But an island is greater than an island merely in some way, and never in such a way as to be so great that nothing greater than it can be thought of.
[3] However, even if we set this aside, there's another problem that Gaunilo's objection runs into. A key point in both arguments, Anselm's and Gaunilo's, is that it is greater to exist than not to exist (i.e., any thought object that can be thought to exist in reality can be thought to be greater than any thought object that is only in the intellect). In Anselm's argument this only comes into play given that we are at a limit-case of greatness: we are at something so great that the only question is whether it also has the greatness of existing or not. And because of the nature of this limit-case, that it is that than which nothing greater can be thought, it must have the greatness of existing. If we are only comparing islands, however, we are not at the limit-case of greatness, unless we can also show that nothing can be conceived that is greater than the greatest island (which obviously we cannot, since it is false). Thus the parallel breaks down in yet another way.
[4] Yet another point. If A is greater than B it is always as something. Thus if an island is that than which no greater island can be thought, it must be greater as something. The question of 'as something' doesn't arise in Anselm's case because it is automatically constrained by the nature of the argument; we are considering greatness of being. In the island case, (C) suggests we are considering greatness relevant to islands (and, indeed, just about everyone takes it in such a way). But if this is so, the Island parallel breaks down at yet another point: the Island objection, taken as a reductio of Anselm's argument, is equivocating on the term 'greater'. The result is that the 'greater to exist in reality' premise is jeopardized in a way that it is not in Anselm's argument.
[5] Suppose, however, that we were to to take (C) in the following further-refined sense:
(E) that island than which no island greater as a being can be thought
What then? Unfortunately for the Island objection, the answer isn't helpful for the pro-Gaunilo side. For, as noted above, the reason 'greater as a being' is relevant to existence in Anselm's description (A) is that we are at a limit-case of greatness. (E) is not such a limit-case; for if the island than which no island greater as a being can be thought does not exist, this suggests nothing unless the only greatness left to consider is existence itself. That is, if there are other greatnesses of being besides existence that are involved in being a great island, (E) doesn't even suggest the existence of the island than which no island greater as a being can be thought.
[6] Beyond that, however, if we stipulate that the only greatness left to consider is existence, all (E) suggests is that the island than which no island greater as a being can be thought is just an island that actually exists, because any island that actually exists will be greater on this stipulation than any island that does not. This problem does not arise on Anselm's formulation of (A).
[7] Further still, as a smaller additional problem, (E) is only an issue if islands are not all on a par in terms of greatness of being. If they are on a par, and islands really exist, (E) is satisfied by any really existing island. By the same token, if no islands really existed, but only existed in the mind, (E) would be satisfied by every island existing in the mind. However, it is more plausible to say that islands, considered as beings, are all on a par in terms with greatness, because they are all the same basic thing (islands, namely, dry-land ecosystems encircled by water) than to say that all things, considered as beings, are on a par in terms with greatness. Gaunilo's objection depends on being plausibly parallel to Anselm's at every relevant point; but whether it is parallel even on this basic point is more murky than the pro-Guanilo camp wants to admit.
Conceivably one or two of these equivocations could be evaded; but (1) it requires more effort than Gaunilo supporters ever put forward; (2) it's unlikely that all of them can be neutralized. The objection is flawed through and through; it's clever, to be sure, because it makes use of an apparent, but purely verbal, similarity. The verbal similarity hides rooms upon rooms filled with equivocations, though; it is doubtful that the Island objection can ever be made genuinely parallel to Anselm's argument. If so, it can never be the reductio it is put forward to be. It is a clever bit of philosophical sleight-of-hand, useful for fooling those who don't take the trouble to analyze it, and nothing more. It's the philosophical equivalent of a magic trick; it works by misdirection. The real issues that Anselm's argument raises are elsewhere.
