Also: appeal to less than absolute certainty: "There's no way we can know for sure, since we weren't there. We can make judgments, but we don't have knowledge." Or, when you say "X", someone responds "are you really sure of X?", and you say "I'm 99% sure of X", they accuse you of retreating from your position: "Oh, well you didn't say that before; you just said 'X', which is an expression of absolute certainty" -- thereby interrupting the conversation and dodging the disagreement.

Closely related to the appeal to permanent unknowability and the appeal to humility.