_What is the Sound of the Single Hand? When you clap together both hands a sharp sound is heard; when you raise the one hand there is neither sound nor smell. . . .
This is something that can by no means be heard with the ear. If conceptions and discriminations are not mixed within it and it is quite apart from seeing, hearing, perceiving, and knowing, and if, while walking, standing, sitting, and reclining, you proceed straightforwardly without interruption in the study of this koan, then in the place where reason is exhausted and words are ended, you will suddenly . . . break down the cave of ignorance.. . . At this time the basis of mind, consciousness, and emotion is suddenly shattered.19
But this is not the end; rather it is the beginning. After a disciple has penetrated this koan, he receives koans of increasing difficulty. From Hakuin's own experience he knew that _satori _experiences could be repeated and could become ever deeper and more meaningful. Although he himself never chose to overtly systematize and categorize koans, his heirs did not hesitate to do so, creating the structure that is modern Rinzai Zen.
How did Zen finally emerge, after all the centuries and the convolutions? As Hakuin's descendants taught Zen, a monk entering the monastery was assigned a koan chosen by the master. He was expected to meditate on this koan until his _kensho_, his first glimmer of satori, which might require two to three years. After this a new phase of study began. The monk was then expected to work his way through a program of koans, requiring as much as a decade more, after which he might meditate on his own, in seclusion, for a time longer.20
The master worked with monks individually (a practice reputedly left over from the time when Chinese-speaking masters had to communicate in writing) via a face-to-face interview (_senzen_) reminiscent of a Marine Corps drill instructor harassing a recruit. The monk would bow to the master, seat himself, and
submit his attempt at resolution of the koan. The master might either acknowledge his insight, give him some oblique guidance, or simply greet him with stony silence and ring for the next recruit--signifying an unsatisfactory answer.