Hakuin not only redefined meditation, he also revitalized koan practice among full-time Zen monks and ultimately brought on a renaissance of Rinzai Zen itself. He formalized the idea of several stages of enlightenment (based on his own experience of increasingly deep satori) as well as a practice that supported this growth. But most of all Hakuin was dismayed by what he considered to be the complete misunderstanding of koan practice in Japan. Monks had memorized so many anecdotes about the ancient Chinese masters that they thought they could signify the resolution of a koan by some insincere theatrics. _[0]f the monks who move about like clouds and water, eight or nine out of ten will boast loudly that they have not the slightest doubt about the essential meaning of any of the seventeen hundred koans that have been handed down. . . . If you test them with one of these koans, some will raise their fists, others will shout "_katsu_," but most of them will strike the floor with their hands. If you press them just a little bit, you will find that they have in no way seen into their own natures, have no learning whatsoever, and are only illiterate, boorish, sightless men.16 _ Hakuin breathed new life back into koan theory. For instance, he seems the first Japanese master to take a psychological interest in the koan and its workings. He believed a koan should engender a "great doubt" in the mind of a novice, and through this great doubt lead him to the first enlightenment or _kensho_.17 Initially he had advocated the "Mu" koan for beginners, but late in life he came up with the famous "What is the sound of one hand clapping?"18 As he described this koan in a letter to a laywoman: _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.