the paradox that if “This sentence is not true” is true, then it is not true, and if it is not true, then it is true. This example shows that certain formulations of words, though grammatically correct, are logically nonsensical. The English philosopher Bertrand Russell, in developing the theory of types, used the following illustration: the statement, “I am lying” is true only if it is false, and false if it is true. Epimenides, a 6th-century-BC Cretan prophet, first recorded such a paradox.