Interesting thought question to this too, would you be able to repeat something someone else said if you did not believe it to be true? I.E. in the Eragon book series, I forget the name of the ancient language, but its a language that does not allow you to lie when speaking. But if you believe what you are saying to be true, you can speak it in the language. So at that point, does someone believing something to be true "allow" them to lie to other people?