Philosopher J. P. Moreland defines self-refutation: “When a statement fails to satisfy itself (i.e., to conform to its own criteria of validity or acceptability), it is self-refuting…. Consider some examples. ‘I cannot say a word in English’ is self-refuting when uttered in English. ‘I do not exist’ is self-refuting, for one must exist to utter it. The claim ‘there are no truths’ is self-refuting. If it is false, then it is false. But if it is true, then it is false as well, for in that case there would be no truths, including the statement itself.
— Greg Koukl and Francis Beckwith, from Relativism: Feet Firmly Planted in Mid-Air, p. 82