I was at my parents' house for dinner the other night, and somehow the subject of an afterlife came up. My mother asserted that she "knows" she would go to Heaven if she died right now, and my father and I both corrected her, telling her she doesn't know, but she believes. She continued to argue against us for a few minutes, refusing to acknowledge the difference between knowing a fact and believing something that is unprovable. It was very frustrating, and I held back from arguing too much because I didn't want to announce to my dad that I'm an atheist.
What arguments are there that will actually cause a theist to recognize the nature of their "knowledge of God" as subjective and not objective? Belief and not knowledge? I've actually had theists tell me that even though it can't be proven to anyone else, they still "know, objectively" that God exists. The example given was that if I talk to my cousin today and then tell a friend who's never met this cousin, "Hey, I talked to my cousin" tomorrow, that would seem subjective if I can't physically bring my cousin to meet my friend, but I would still know objectively that my cousin exists and I spoke with her. The difference, of course, is that the existence of my cousin can still be proven in one way or another, while God's existence cannot; however, explaining this never seems to bring this sort of person to admit the difference.
No amount of reason has ever worked on these people, and I've got to admit that while my mom handles my atheism pretty well, it's incredibly frustrating that I can't get her to admit the most basic of facts about belief, and none of them would be inherently damaging to that belief, so it's not as if she could "protect" her faith by avoiding them. I wonder if she's honestly naive enough that she can't grasp the difference between belief and knowledge, or if she's just averse to thinking critically about her faith because it's hard. So... if this comes up again, how might I try explaining the concept to her again in a way that might make her stop repeating her mantra of "I know" and actually listen to what I'm saying?
I don't want to appear overly confrontational over this if it does come back up between us, but I value intellectual honesty, and it bothers me when one of the most important people in my life won't be intellectually honest. I think that gently engaging her in these sorts of discussions and helping her to see where, for example, her beliefs are not equivalent to real knowledge will aid her in understanding my atheism, and perhaps give her some comfort in that area.