On the next day I came across a native who said: "My father once said that he and I are different types, one a knight and one a knave."(Source: To Mock a Mockingbird and Other Logic Puzzles: Including an Amazing Adventure in Combinatory Logic by Raymond Smullyan)
Is it possible that his father really said that?
If the native is a knight, then his claim that his father said the two are of different types is true. But if the father is a knight, the two are not of different types. And if the father is a knave, then his statement is true. If, on the other hand, the native in question is a knave, then his father did not in fact say that. In either case, it couldn't have happened.
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