Musō Soseki (1275–1351), a Japanese contemporary of Zhongfeng Mingben, relativized the use of koans. The study of koans had become popular in Japan, due to the influence of Chinese masters such as Zhongfeng Mingben. Despite belonging to the Rinzai-school, Musō Soseki also made extensive use of "richi" (teaching), explaining the sutras, instead of "kikan" (koan). According to Musō Soseki, both are "upaya", "skillful means" meant to educate students. Musō Soseki called both "shōkogyu", "little jewels", tools to help the student to attain satori.