Knights always tell the truth,liars always lie,and knaves alternate between truths and lies.

Two people named Jimmy and Johnny make the following claims.

Jimmy:I am a knave.
Johnny:Jimmy is not a knight.
Jimmy:Johnny is a knave.
Johnny:Jimmy is a knave.

What are each?

From Jimmy's first statement, Jimmy is either a liar or a knave. 

If Jimmy is a liar, then, by his second statement, Johnny is not a knave. If Jimmy is a knave, then, as his first statement being true, his second statement is false, thus, again, Johnny is not a knave.

Johnny's first statement, being true, indicates that Johnny is either a knight or knave. But as established by Jimmy's statements, Johnny cannot be a knave, thus must be a knight. 

As a knight, Johnny's second statement is true, thus Jimmy must be a knave. 

Posted by Dej Mar on 2008-07-01 04:55:02