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.
That Mu exists in the natural world investigated by science is evident. […] The dualistic mind tends to think of Mu occurrences in nature as a kind of contextual cheating, or irrelevance, but Mu is found through all scientific investigation, and nature doesn't cheat, and nature's answers are never irrelevant. It's a great mistake, a kind of dishonesty to sweep nature's Mu answers under the carpet. […]
When your answer to a test is indeterminate it means one of two things: that your test procedures aren't doing what you think they are or that your understanding of the context of the question needs to be enlarged. Check your tests and restudy the question. Don't throw away those Mu answers! They're every bit as vital as the yes and no answers. They're more vital. They're the ones you grow on.
--Robert Pirsig, Zen and the Art of Motorcycle Maintenance