Do you tell the truth?
There is no way to be certain just by asking. Someone who is lying would lie about telling the truth.The "Liar's Paradox" is that no one can rationally answer a question about the truth by saying "I am lying." This is clearly because if you are telling the truth, you say "I am telling the truth" and if you are actually lying (about lying), you would again say "I am telling the truth" (a lie).If you said you were lying, you would have to be telling the truth, but you're not because you are lying. This is similar to the double-negative paradigm ("He's not right...he's just not wrong").