In the 6th century BC, the ancient Greek Cretan Epimenides famously said: All Cretans lie. Did he tell the truth or a lie? If he is telling the truth, since he is also one of the Cretans, he also lies, so he is lying; if he is lying, some Cretans do not lie, He could also be one of these Cretans who don't lie, so he could be telling the truth. This is called the "Liar Paradox". In the 4th century BC, Eubulides of the Meghalites rephrased the paradox as: A man said: What I am saying is a lie. Is this sentence true or false? If the sentence is true, it speaks of the true case, and it says itself false, so it is false; if the sentence is false, it speaks of the true case, and It says it itself is false, so it is telling the truth. Thus, the statement is true if and only if the statement is false. This kind of sentence, whose truth can be deduced from its falsehood, and whose truth can be deduced from its falsehood, is generally called a "paradox." A less rigorous statement is: if two self-contradictory propositions or the equivalence of such two propositions are obtained through logical derivation that seems to be correct and valid, starting from obvious and reasonable premises, then it is said to be paradoxical. Argument. The point here is that the premise of reasoning is clearly reasonable, the process of reasoning seems logical, and the result of reasoning is a self-contradictory proposition or an equivalence of such a proposition.

In the 6th century BC, the ancient Greek Cretan Epimenides famously said: All Cretans lie. Did he tell the truth or a lie? If he is telling the truth, since he is also one of the Cretans, he also lies, so he is lying; if he is lying, some Cretans do not lie, He could also be one of these Cretans who don't lie, so he could be telling the truth. This is called the "Liar Paradox". In the 4th century BC, Eubulides of the Meghalites rephrased the paradox as: A man said: What I am saying is a lie. Is this sentence true or false? If the sentence is true, it speaks of the true case, and it says itself false, so it is false; if the sentence is false, it speaks of the true case, and It says it itself is false, so it is telling the truth. Thus, the statement is true if and only if the statement is false. This kind of sentence, whose truth can be deduced from its falsehood, and whose truth can be deduced from its falsehood, is generally called a "paradox." A less rigorous statement is: if two self-contradictory propositions or the equivalence of such two propositions are obtained through logical derivation that seems to be correct and valid, starting from obvious and reasonable premises, then it is said to be paradoxical. Argument. The point here is that the premise of reasoning is clearly reasonable, the process of reasoning seems logical, and the result of reasoning is a self-contradictory proposition or an equivalence of such a proposition.