Quine's paradox

Quine's paradox is a puzzle about words. It asks whether a sentence can be true and false at the same time. The sentence in the puzzle is: "This sentence is false". If the sentence is true, it means that it is false. But if it is false, then it must be true! So it is both true and false at the same time, which is impossible. Quine's paradox shows us that it's not always easy to figure out what is true and what isn't, even when we're looking at just one sentence.