Knights always tell the truth,liars always lie,and knaves alternate between truths and lies.
Suppose you ask a native,"Are you a knight,a liar,or a knave?"
The native answers,and you are able to figure out what he is.
What is the native?
(In reply to answer
by K Sengupta)
A native can either idebtify himself as a knight, a knave or a liar.
In the first case, the native as a knight will truthfully do so, while the native as a liar(or, knave) will do so falsely.
In the second case, the native can truthfully do so if he is a knave, or falsely do so if he is a liar.
In the third case, the native cannot do so if he is a knight. He cannot do so if he is a liar, for then he will be speaking the truth. The only possibility is that he will speak falsely as a knave in identifying himself as a liar.
Consequently, the native is a knave and he identified himself as a liar.