How is it possible that people from other religions have the properly basic belief that their God exists? If there is a god, shouldn’t there be just one religion whose members feel so strongly about his existence?
We need to clarify what “properly basic beliefs” are. Such beliefs are the product of one’s experience. You have a firsthand experience of ‘X’ and are justified in your beliefs about ‘X’ based on that firsthand experience. If you visit the lake, then you have a firsthand experience of having seen the lake. You are, therefore, justified in your belief in the lake.
The Christian’s belief in God is properly basic because of the internal witness of the Holy Spirit. We are justified in believing in God because we know God.
It is the nature of firsthand experiences that we cannot share them. Perhaps I can tell you about the lake I saw, but I cannot make you have had the experience of “seeing the lake.” Because of this, what is properly basic for you may not be properly basic for me. Perhaps I only believe in the lake because of your testimony, in which my belief will be non-basic.
When it comes to religious experiences, we do not have access to adherents’ experiences with other religions. We cannot say, therefore, that they have a religious experience as we do. We would deny that they have such experiences. Since we believe that Shiva does not exist, we would deny that any Hindu has a real firsthand Shiva experience.
Imagine if I told you that I had met the Easter Bunny. You don’t believe the Easter Bunny exists, and so you would deny that I had such an experience (even if you became convinced that I * thought* I had).
In short, the reported religious experiences of others cannot be more persuasive to us than our own firsthand experience of God.