William James

William James, co-founder of American Pragmatism, taught me something wonderful last semester, so let me share. All of our beliefs rest on other beliefs. Those beliefs rest on further beliefs, etc., until we reach our foundational beliefs. These beliefs can vary widely, from 'There is an external world', to 'God exists', to modus ponens. But the fact is, these beliefs are foundationless--that is what makes them foundational. To the individual, they are seen as self-evident. But to someone who disagrees, it is impossible to argue with them. These beliefs are at the center of our belief-web, and as such are not accesible to alteration, without starting from scratch, which is most likely psychologically impossible.
But when you find yourself in an argument with someone and you reach a point at which foundational beliefs differ, just remember that theirs has as much grounding as yours; none. As long as a person's beliefs are consistent with one another, and as long as their inferences and deductions are not flawed, their system is as good as yours.
So I guess the lesson here is tolerance.
James says, and I agree, that any belief system which is self-consistent and explains all given evidence (sensible evidence, that is), it is as good a system as any.
So, sorry pretentious scientists, but a reflective and rational theist is on as good a ground as you are. I have to remind myself of this too, as I tend to take science's side on most matters. But unfortunately, unless you can point out an inconsistency, the creationist is perfectly ok to say God put dinosaur bones there as a test, or something like that.
Don't worry--when I first realized this I thought it meant all meaningful argument was impossible, until I realized that everyone's belief system (including my own) has so many logical inconsistencies that just working these inconsistencies out creates endless debate possibilities. For one fun example, how about the fact that most Christians believe in ghosts even though Christian theology doesn't allow such a thing.
I'm not trying to rip into Christians--scientists do the same kind of shit.

Just remember, be tolerant of anyone who uses good reasoning from their beliefs, whatever those beliefs may be.