The Mumonkan, a shorter work, was assembled in 1228 by the Ch'an monk Wu-men Hui-k'ai (1183-1260) and consists of forty-eight koans, together with an explanatory comment and a verse. Some of the koans in the Mumonkan also appear in the _Blue Cliff Record_. The Mumonkan is usually preferred in the Japanese summer, since its koans are briefer and less fatiguing.10
The koan was an invention of the Sung Dynasty (960-1279), an era of consolidation in the Chinese empire after the demise of the T'ang and passage of a war-torn interlude known as the Five Dynasties (907-60). Although Sung Ch'an seemed to be booming, Buddhism in general continued the decline that began with the Great Persecution of 845. For example, the number of registered monks dropped from around 400,000 in 1021 to approximately half that number a scant half-century later.11 But the monks who did come probably had higher education than previously, for the Sung educational system was the world's best at the time. Colleges were established nationwide, not just in the sophisticated metropolitan areas, and scholarship flourished. Whether this was good for Ch'an is not a simple question. The hardy rural monks who had passed beyond the Buddhist scriptures made Ch'an what it was. Could the powers of the antirational be preserved in an atmosphere where the greatest respect was reserved for those who spent years memorizing the Chinese classics? The answer to this was to rest with the koan.
The Ch'an master Ta-hui (1089-1163), who perfected the koan technique, was rumored to be a reincarnation of Lin-chi. Born in Anhwei province, located about halfway between the older capitals of the north and the Ch'an centers in the south, he was said to be both pious and precocious, becoming a devoted monk at age seventeen while assiduously reading and absorbing the teachings of the five houses.12 At age nineteen, he began his obligatory travels, roaming from master to master. One of his first teachers reportedly interviewed him on the koans in the collection now known as the _Blue Cliff Record_, but he did so by not speaking a word and thereby forcing Ta-hui to work them out for himself. Ta-hui also experimented with the Ts'ao-tung teachings, but early on began to question the straitlaced, quietistic approach of that house. He finally was directed to the Szechuan teacher Yuan-wu K'o-ch'in of the Lin-chi school, beginning the association that would move him to the forefront of the struggle to save Ch'an via the koan.