Definition
Mu is the Zen answer attributed to the Chinese master Joshu when asked whether a dog has Buddha-nature. Mu (Chinese: 無; Japanese: む) literally means "nothing" or "without," but its function in the koan is to refuse the dichotomy implicit in the question. The right answer is not yes, not no — it is to recognize that the question presupposes a category the answer cannot satisfy from inside.
Why it matters
How it works
To apply the mu move to a stuck question: examine the question for hidden assumptions. If the question presupposes a yes/no answer, ask whether the categories on which the dichotomy depends actually apply. If they do not, the right response is not to choose a side but to dissolve the question by showing the categories are inapplicable. This requires meta-reasoning about the framing.