Sorai was born the second son of a samurai (a warrior) who was the personal physician of Tokugawa Tsunayoshi (徳川綱吉). Tsunayoshi would become the fifth shogun. Sorai studied the Zhu Xi version of Song Confucianism, and by 1690 he became a private teacher of Chinese classics. In 1696, he started serving Yanagisawa Yoshiyasu, a senior councilor to Tsunayoshi. Tsunayoshi died in 1709. At that time Sorai stopped using the teachings of Zhu Xi and started to develop his own philosophy and school. Sorai is credited with the creation of kō shōgi, an unusual form of chess.