"The truth value of the statement cannot be evaluated because the statement refers to the truth value of itself." - I am not sure I understand this, or agree with would probably be a better statement. I think, hope, we are not talking about the impossibility to test all Cretans because there are too many or something like that, because there is a finite number of Cretans and we can just start testing one by one with a clearly defined meaning of the word "liar" as someone who always tells a lie. And, as soon as we find one that is telling the truth we can conclude that the statement is a lie. And, I would actually argue that the statement is, clearly, a lie, since the negation of All is not exclusively None, but also Some. Some is also ¬All. Therefore, by concluding that Epimenides told a lie we are not creating a contradiction, our conclusion is logically valid.
Unless the problem is the definition of the word liar as someone who sometimes tells the truth which, I would agree, seems impossible to test.-- Pedja (speak up, contributions) 14:26, 8 March 2013 (UTC)
The most succinct example I have seen is "This statement is false". Can't remember what book it was from, but it used the terms Knights, Knaves and Normals. 126.96.36.199 (talk) 15:13, 12 June 2013 (UTC)