I keep seeing the following koan:
A monk asked Zhàozhōu, "Does a dog have Buddha nature or not?" Zhaozhou said, "Wú".
What does this mean and why is it important?
More specifically: Does "Wú" mean "no" in this context, or does it mean "the question doesn't make sense and therefore cannot be answered"? I've seen both interpretations, which one is correct?
We should really have a rule on here not to provide koan answers! It's so important that you figure them out for yourself! Written out, the answers become hollow and never approach their true 'meaning'. That said (and no spoilers follow!)...
Mu does mean no, but it also can translate as blankness, voidness, or absence. That should ring a bell regarding the concept of emptiness or shunyata. The koan really doesn't have anything to do with dogs or whether or not they have a Buddha nature. It has more to do with this idea of emptiness - what it is and the initial experience of it. The monk in this koan is all caught up in scholasticism and conceptualism. He's using his small mind to try and understand a concept that it's just not capable of of apprehending. Zhaozhou's answer is an attempt to shake that monk out of his smaller way of thinking and point him instead to mu - the true essence of Zen.
People often report this koan with out explaining the surface meaning. Chinese at the time considered dogs nasty dirty animals, that hold the same position as pigs in the western mind. Pigs or cockroaches or those parasites that burrow into your eyes. So the surface question is can the most contemptible being become enlightened.
The surface meaning of the most common answer, Mu is Buddhist jargon, meaning emptiness, sunyata. In the Mahayana system, you are enlightened when you realize the truth of sunyata, i.e. that you have no self (no atman), everything changes over time and various other things that I don't have space for here.
In my opinion, koan practice is a practice. You think about a question and always are told that your answer is wrong. During this process, many people report flashes of insight where they subjectively feel that they have grasped the answer, i.e. satori or sudden enlightenment. Reasoning takes time, so sudden enlightenment can't be done in step by step reasoning.
In China, there was a huge multiyear (multi decade?) discussion on if enlightenment was a matter of following steps or if it was something that happened to you in a flash. In China and Japan, the sudden enlightenment proponents won.
Some modern critics say that especially in Japan with a new funerary and post mortem outlook, have moved onto a form of Zen where sunyata is a sudden realization that you do have an immortal self, which contradicts early Buddhist thought.
I have always found koans to be useful tools for thought. Through study of the dharma, interaction with the sangha and a variety of other means we reach new insights that are much like dull tools. Through their use applied against the situations in various koan we find their true worth. There is no right answer to a grinding wheel.
