The following two facts are known about Adam, Bert, and Carl:

1) Of Adam, Bert, and Carl, there is one knight, one knave, and one liar.
2) Adam said once, "Bert said that Carl isn't a knight."

Can you ask one yes/no question to one person and figure out who is who? If not, how many questions must you ask?

(In reply to it can be done in one question. by joshua imperato)

Aren't you assuming that Bert actually said anything at all about Carl ? 'Adam said once, "Bert said that Carl isn't a knight" ' doesn't mean that Bert didn't really say "I hate this winter weather", or made any statement at all. 

If Bert actually said what Adam quoted him as saying, and Bert's  statement is true, then if Adam answers "Yes, I am a Knight", then Adam could be the Knight, truthfully quoting Bert the Knave truthfully denying that Carl the Liar was a Knight, and then truthfully claiming Knightly status for himself (two truths by Adam); or Adam could be the Knave, who truthfully quoted Bert the Knight as truthfully denying that Carl the Liar was a Knight, and then lying about being a Knight himself (a truth-lie combination). On the other hand, if Bert really said it, but it was a lie, then Adam the Knave was truthfully quoting Bert the Liar's lie about Carl not being the Knight, and then lying about his own identity (a truth-lie combination). Finally, if Bert had really said nothing at all, and Adam answers "Yes, I am a Knight", he must be a Liar (a lie-lie combination), and the other two could be either of the two remaining possibilities.       

Edited on February 18, 2005, 8:50 pm

Posted by Penny on 2005-02-18 20:45:52