Joel S. has an informative and thoughtful review of Miroslav Volf's new book Allah: A Christian Response [ht: Justin Taylor]. This post is adapted from a comment I left on Joel's review, with significant expansions and modifications.
I like a lot of what Volf is saying, but I think Joel's concerns about the book are important things to be concerned about, especially the ones numbered 2 or higher. I disagree with his take on the substantive issues for concern 1, and I've been on record defending my view on the matter for quite some time.
The issue is whether I refer to the same being a Muslim refers to when we both talk about God. The Muslim uses the word 'Allah'. I use 'God'. Volf apparently argues that the Christian view of God and the Muslim view of God are sufficiently similar to ensure that they both will refer to the same being. I think that's a terrible argument. Any argument based on sufficient similarity is going to fail pretty quickly once we look to the essential Trinitarian nature of God. That's a pretty core element of the Christian view, if we're basing the reference of terms on actual metaphysics.
But of course language doesn't work that way. When people starting talking about water, they weren't doing so with full understanding of its chemical structure. If two groups with competing scientific theories about what water really is still referred to the same stuff and called it water, it would be nothing short of obtuse to claim that they referred to different stuff. Their historical and causal connection with that stuff is what grounds their reference to it with their terms, even though they had conflicting theories about what it is in its nature.
Similarly, the general Abrahamic tradition, confused as it is at some historical points, grounds the Islamic reference to God when they use the word 'Allah'. They refer to the being who interacted with human beings in the patriarchal period, through the human king they call the prophet David, and (and this is key) through that guy that they call the prophet Jesus. Surely they believe false things about Jesus, by any Christian standard. But it's the historic Jesus whom they claim to be a prophet, whom they claim to be returning someday, whom they claim did not die on the cross but was replaced by Jesus. They get Jesus' nature very wrong, but they refer to him when they do so, just as scientists got the nature of heat wrong when they thought it a substance but still referred to it (the kinetic energy) when they talked about it.
So if the question of whether Muslims worship the same God means whether the being they call Allah is the same being we call God, then the answer is obviously yes. But Volf is wrong to base it on similarity. He doesn't seem aware of causal theories of reference or any such thing.
On the other hand, if the question of whether Muslims worship the same God means whether their worship is correct worship, then that's another question entirely. It shouldn't be confused with the metaphysical question of whether the same being is referred to by Christians and Muslims. I've seen too many people start with their stance that Muslim worship of God involves actual reference to the same God Christians worship and then conclude that Muslim worship is equivalent to Christian worship. That inference seems to me to be utterly fallacious.