Here is a link to an interesting piece in Science on the psychology of faith. The question raised relates to the cognitive basis for one's sense of religious belief. As the article states:
"Many people with religious convictions feel that their faith is rock solid. But a new study finds that prompting people to engage in analytical thinking can cause their religious beliefs to waver, if only a little. Researchers say the findings have potentially significant implications for understanding the cognitive underpinnings of religion."
While some folks may be offended by the very idea of the study, I think it's worth reading. Also I wonder about the difference between faith in doctrine or dogma vs. the sense of conviction arising from experience. In some sense this is the difference between religion in its institutional settings and spirituality in its personal expression.