Yes and no…this or that…one or zero. In the basis of this elementary two-term discrimination, all human knowledge is built up. The demonstration of this is the computer memory that stores all knowledge in the form of binary information. It contains ones and zeroes, that’s all.
Because we’re unaccustomed to it, we don’t usually see that there’s a third possible logical term equal to yes and no which is capable of our understanding in an unrecognized direction. We don’t even have term for it, so I’ll have to use the Japanese mu.
Mu means “no thing.” Like “quality” it points outside the process of dualistic discrimination. Mu simply says, “no class: not one, not zero, not yes, not no.” It states that the context of the question is such that a yes and a no answer is in error and should not be given. “Unask the question” is what it says.
Mu becomes appropriate when the context of the question becomes too small for the truth of the answer. When the Zen monk was asked whether a dog had Buddha nature he said “Mu,” meaning that if he answered either way he was answering incorrectly. The Buddha nature cannot be captured by yes or no questions…
–Robert Pirsig, Zen and the Art of Motorcycle Maintenance