Jake had asked about my views of whether and how Christians, Jews and Muslims worship the same God. This is not an issue I generally have much interest in, because I'm one of those people who think it's just obvious that they do: all major monotheisms worship the same God, and so the question is just how accurately or inaccurately, how well or badly. I wouldn't ordinarily talk about it, then, unless asked; but as I was asked, and as it came up recently at First Things, where Gerald R. McDermott argues that "the God of the Qur'an is not the God of the Bible", I suppose now is a good time to talk about it. I think there are certain basic points that need to be kept in mind as our background.
(1) All of the world's major monotheisms are explicitly inter-referent. Christians insist that they worship the same God that the Jews claim to worship. Muslims insist that they worship the same God that Jews and Christians claim to worship. Sikhs refer to Sufi Muslim worship of God as true worship of God. The list can be continued. This needs to be given weight. When Muslims are asked, "What do you say God has actually done?" among the things they will be pointing to are things that Jews and Christians will point to as things that God has actually done.
(2) Talking about God is not like talking about some guy you happen to know from somewhere; there are lots of unique descriptions of God, things that can necessarily only genuinely be applied to God if they can be applied at all. A lot of these are mutually recognized by Christians, Jews, and Muslims. All three, for instance, recognize God as Creator, and as having revealed himself to Abraham and the Jewish prophets.
When you look at the kinds of arguments people give in order to say that (for instance) Muslims do not worship the same God as Christians, one finds that there's usually a slippage in figure of speech going on. What they're really talking about is difference of worship, not difference of God. Both McDermott and Volf (to whom he is responding) focus almost solely on this. But using this to talk about different Gods is a figure of speech. We find a similar figure of speech, incidentally, when people distinguish the God of the philosophers from the God of Abraham, Isaac, and Jacob: this is not actually a division between what philosophers and Christians talk about, but a hyperbolic way of talking about how philosophers and Christians talk about God. If they weren't talking about the same thing, there wouldn't be an issue; it would be a purely verbal equivocation to put them together, as if one said that there is a very big difference between the banks of the river and the banks on Wall Street, or between the Abraham in the Bible and the Abraham who led the United States in the Civil War. That's true, but it's true because the only relevance of one to the other is that they happen to be described by homonyms. Similarly, the only reasonable force of a distinction between the God of the philosophers and the God of Abraham, Isaac, and Jacob is to say that one of the two groups, philosophers or the spiritual children of Abraham, are talking about God badly, or that one of the two groups is doing so in a defective way in comparison with the other. Similarly, the only sensible point a person can be making in saying that the God of Judaism is not the God of Christianity is to be saying that one of the two groups, Christians or Jews, are doing things wrong. And it's important to emphasize, again, that this is a hyperbole to make a specific kind of point; it is not a general principle that can be applied straightforwardly to every kind of case.
Incidentally, when philosophers talk about this subject they tend to talk about reference and sense. Done well, I think this can clarify things, but I think it's ultimately a mistake in approach. The difference put forward in talking about hte difference between the God of the philosophers and the God of Abraham, Isaac, and Jacob, for instance, simply doesn't depend on whether they have the same referent -- any difference of meaning relevant to whatever the point at hand is will do, even if it's purely a matter of tone or contextual association. And I think the tendency to talk about the God of Muslims being different from the God of Christians is quite parallel.
We see this done elsewhere. I remember reading something by an analytic philosopher of religion -- Wolterstorff, I think -- who was talking about Aquinas and did so by repeatedly talking about Aquinas's "Plotinian God". It was very aggravating. Part of it, of course, was that Aquinas even at his most Platonistic is not actually very Plotinian, despite some very indirect connections to Plotinus. But the point of it, of course, was really not about Aquinas's God at all, but about some things that Aquinas says about God that the author wanted to treat as wrong. It would have made no sense to go through Aquinas's commentary on Romans, for instance, and point out all the places that he talks about his "Plotinian God". It was a figure of speech, and in context was largely a rhetorical bridge to avoid having to argue certain things in plain sight. It wouldn't have been a problem at all if the argument had been aboveboard about the limitations of the hyperbole. I can point to Berkeley's texts and talk all day about Berkeley's very Neoplatonist God, and it in no way and at no point suggests that Berkeley was not an orthodox member of the Church of England, or that he was at any point not talking about "the Anglican God". This is all because I am not actually talking about Berkeley's God in these contexts; I am using a figure of speech to talk about Berkeley's talk about God. Likewise, in the case we're talking about here, the discussion is not actually about God at all, but about belief and worship.
The whole issue, then, seems to me to involve foundering on figures of speech, rather than being one of real substance. You can legitimately talk about the God of Muslims and the God of Christians as being different; this is really a figure of speech for talking about the differences between Muslims and Christians. And you can legitimately talk about them being the same; because otherwise the difference wouldn't be worth mentioning. It's just a matter of keeping in mind context, and not treating hyperbolic figure of speech as a straight literal expression.