As a starry-eyed perennialist I have never been troubled by the variety of religions all claiming to be true. I have a way of bracketing that 'true' and I'll tell you about it sometime but it's a strange thing that philosophers who draw a bead on this variety as indicating general dubiousness may themselves espouse a philosophy which others in the trade regard as obviously false. Sorry, make that a muddle. It does seem to be impossible to decide between different systems because the ways of deciding are themselves in contention. It's not just the concept of truth, but the very definition of what a concept is. And so on and so forth and on the other hand I suspect.