Cretan paradox
the liar's paradox
Today this word meansThe logic problem of a self-referring sentence that can be neither true nor false.
From the sixth-century BC Cretan Epimenides, said to have declared that "all Cretans are always liars."
It became famous when the New Testament's Epistle to Titus quoted the line verbatim.
In the twentieth century this problem of self-reference became a major theme again in logic and the foundations of mathematics.
Worth noting
Strictly speaking it is not a full paradox. If the sentence is false, then "some Cretan sometimes tells the truth" — and it resolves without contradiction. The true paradox is "this sentence is false."