Mu

In the world of Zen, the background theme of Zendo, a question can sometimes neither be answered with "yes" or "no". In this case, mu is the unanswer, which unasks the question.

In Zendo, "mu" may be the Master's answer to an improper or ill-formed question. If a student's guess at the secret rule were disallowed (for example, because of the Spock rule), the Master could rightly return the guessing stone to the student and answer "mu," explaining why the student's guess can't be answered in another way. For example, if the guess were "Do the two pyramids have to be touching?" which pre-supposes that there are at least two pyramids in a koan, the Master should answer "mu" and help the student to put their ideas into the form of Zendo rules.