  It has long been known that the sentence, (1), produces a paradox, the so-called liar's paradox: it seems impossible consistently to maintain that (1) is true, and impossible consistently to maintain that (1) is not true: if (1) is true, then (1) says, truly, that (1) is not true so that (1) is not true; on the other hand, if (1) is not true, then what (1) says is the case, i.e., (1) is true. (For details, see Section 1, below.) Given such a paradox, one might be sceptical of the notion of truth, or at least of the prospects of giving a scientifically respectable account of truth. 