"Well, it's either true or not true, and you either know it or you don't, and I don't think you being evil affects those odds either way - I don't think evil people know more or fewer things, or that you being evil would make it likelier or less likely that there's a way to find out about it for sure or vice versa. Well, maybe vice versa, if there were a way to find out and you knew it and decided not to be evil since somebody could find out if you were, but that's not a very big slice of maybe. But whether it's true or not and whether you know or not, you would want me to think I couldn't know for sure, if you were actually evil. ...No, that's not quite right, is it, because maybe you could make up a test and then pass it, so I take it back."