This is from a recent post on the blog Leaving Fundamentalism:
From Marianne Talbot, I have learned a useful expression: a self-sealing argument. This is an argument which cannot be refuted, because it doesn’t allow any counter-argument. Almost every fundamentalist argument is self-sealing. This is why, in the end, I concluded that fundamentalism couldn’t possibly be true. Some will accuse me of scientism for this, but I concluded that unless a belief is testable, there’s no point holding it. All will become clearer if I show you an example.
The worst insult a fundamentalist can ever throw at you is ‘unbeliever’…In other words, we’re entirely happy to accept criticism, but it can only come from people who agree with us. And when they apply this criterion, fundamentalists magically find that everybody agrees with them!
As a mechanism to stop people leaving fundamentalism, this is extremely powerful. Remember, salvation is by faith, so if you find yourself straying into unbelief, you’re going to sit on your doubts hard, lest ye lose your salvation entirely.
Now, here’s the thing about self-sealing arguments: You can’t disprove ‘em. They could, in theory, be true. But because there’s no evidence that could ever disprove them, they could equally be false, and the believer would haveno way of knowing.This requires you to believe that God has designed the path to truth in such a way that it looks identical to the path to destruction, and there’s no way of checking which path you’re on. There are other religions with equally self-sealing paths, and adherents who are equally certain they are right. Travellers on all paths claim to have direct experiences of God, so religious experiences don’t offer any clarification.
That’s why I think that if you’re going to base any important decisions on a belief, you have to ask the question “How would I know if I’m wrong?” If the answer is “There’s no way to tell”, you’re on shaky ground.
Click through to read the whole thing.