The Liar Paradox was discovered by the ancient Greeks, and concerned them to a great extent. It concerned them because it seemed to be unsolvable. It seemed to offend the very nature of the world and reason itself. It goes like this...
One day, a traveller comes across a man who is sitting by the road. The man by the road cautions the traveller: "Don't believe a word from the first person that talks to you today - they are lying!" The traveller throws his head back in astonishment.
"But you're the first person to talk to me today!"
The traveller continues on his journey and ponders the strange exclamation made by the man. He thinks: "If he is lying, then he is telling the truth. But if he is telling the truth, then he is lying".
Hence, the paradox. So, which is it?!