Knights and Knaves is a type of logic puzzle.
On a fictional island, all inhabitants are either knights, who always tell the truth, or knaves, who always lie. The puzzles involve a visitor to the island who meets small groups of inhabitants. Usually the aim is for the visitor to deduce the inhabitants' type from their statements, but some puzzles of this type ask for other facts to be deduced. The puzzle may also be to determine a yes/no question which the visitor can ask in order to discover what he needs to know.
An early example of this type of puzzle involves three inhabitants referred to as A, B and C. The visitor asks A what type he is, but does not hear A's answer. B then says "A said that he is a knave" and C says "Don't believe B: he is lying!" To solve the puzzle, note that no inhabitant can say that he is a knave. Therefore B's statement must be untrue, so he is a knave, making C's statement true, so he is a knight. Since A's answer invariably would be "I'm a knight", it is not possible to determine whether A is a knight or knave from the information provided.
In some variations, inhabitants may also be alternators, who alternate between lying and telling the truth, or normals, who can say whatever they want (as in the case of Knight/Knave/Spy puzzles). A further complication is that the inhabitants may answer yes/no questions in their own language, and the visitor knows that "bal" and "da" mean "yes" and "no" but does not know which is which. These types of puzzles were a major inspiration for what has become known as "the hardest logic puzzle ever".
Read more about Knights And Knaves: Examples
Famous quotes containing the words knights and/or knaves:
“Here we have bishops, priests, and deacons, a Censorship Board, vigilant librarians, confraternities and sodalities, Duce Maria, Legions of Mary, Knights of this Christian order and Knights of that one, all surrounding the sinner’s free will in an embattled circle.”
—Sean O’Casey (1884–1964)
“He holds the wire from this box of nerves
Praising the moral error
Of birth and death, the two sad knaves of thieves,
And the hunger’s emperor;
He pulls the chain, the cistern moves.”
—Dylan Thomas (1914–1953)