Philosophers do spend a good deal of time worrying about this matter. Indeed, it is characteristic of many areas of philosophy to be particularly interested in the "unprovable assumptions" with which arguments begin. Two examples: Perceptually-based beliefs---such as that there is a window in front of me---form the starting point for many of our beliefs. (Empiricists hold that all beliefs must be grounded there, but let's set that aside.) But it seems clear, at least to some of us, that these beliefs are not reached by argument from other beliefs. In that sense, they cannot be "proved" on the basis of anything else. How then should we understand how we arrive at such judgements? What is it for one of them to count as known? These are basic questions in the philosophy of perception. In mathematics, theorems are proven from axioms. Axioms, on the other hand, are accepted as true without proof. On what ground do we accept such axioms as, say, that, if there are two sets A and B, then there is a...

I wish I had something helpful to say about this, but I don't know if I do. We should, however, try to get a little clearer on what is at issue. Let's consider something a little simpler, like plays. I think A Comedy of Errors exists. That is, I think there is such a thing as A Comedy of Errors . But that play isn't a physical thing. You can't tear it up, burn it, or spill your coffee on it, though you can tear up, burn, and soak printings of it. If one wants to say that A Comedy of Errors therefore doesn't exist in the same way that its printings do, I suppose that's all right. But that's not because there is some special sense of "exists" at work here. It's because a play is a very different sort of thing from a printing of one. I take it that the same is true of God. God (if God exists) isn't a physical object, so one wouldn't expect God to be made of atoms. What is it that even atheists will concede about God? Let's look at what you say about France. If you are thinking of France as...