The Sound of One Hand Clapping

隻手の音声 (sekishu no onjō): the sound of one hand. It is the koan of Hakuin Ekaku (1686–1769), and he defined it himself in a tract of 1753: when the two hands are struck together there is a sharp sound; when the one hand is raised there is neither sound nor scent. He says there that he had begun setting it five or six years before, after forty-five years of teaching with the older koans, because the great doubt rose more easily in anyone. The one hand is raised; the word clapping in the English title is J. D. Salinger's, from his 1953 epigraph, the form English knows. 音声, a sutra word, is read onjō here and means sound. The question is put to a student, and it is meant to be sat with.