Yamada Koun (山田 耕雲, 1907—1989): Mu!
The story is as you read it: Once a monk asked Joshu, “Does a dog have buddha nature?” Joshu answered, “Mu!” The Chinese character means “nothing,” or “”nonbeing,” or “to have nothing.” Therefore, if we take this answer literally, it means, “No, a dog does not have buddha nature.”
But that is not right. Why not? Because Shakyamuni Buddha declared that all living beings have buddha nature. According to the sutras, when Shakyamuni Buddha attained his great enlightenment, he was astonished by the magnificence of the essential universe and, quite beside himself, exclaimed, “All living beings have buddha nature! But owing to their delusions, they cannot recognise this.”
The monk in the story could not believe these words. To him, buddha nature was the most venerable, most highly developed personality, and a buddha was one who had achieved this perfect personality. How then could a dog have buddha nature? How could a dog be as perfect as Buddha? He could not believe such a thing was possible, so he asked Joshu sincerely, “Does a dog have buddha nature? And Joshu answered, “No!”
Joshu, great as he was, Could not deny Shakyamuni’s affirmation. Therefore his answer does not mean that a dog lacks buddha nature. Then what does Mu mean?
This is the point of the koan. If you try to find any special meaning in Mu, you miss Joshu and you’ll never meet him. You’ll never be able to pass through the barrier of Mu. So what should be done? That is the question! Zen practitioners must try to find the answer by themselves and present it to the roshi. In almost all Japanese zendo, the explanation of Mu will stop at this point. However, I’ll tell you this: Mu has no meaning whatsoever. If you want to solve the problem of Mu, you must become one with it! You must forget yourself in working on it. Your consciousness must be completely absorbed in your practice of Mu.