The term honji suijaku or honchi suijaku (本地垂迹) in Japanese religious terminology refers to a theory widely accepted until the Meiji period according to which Indian Buddhist deities choose to appear in Japan as native kami to more easily convert and save the Japanese.[1][2] The theory states that some kami (but not all) are local manifestations (the suijaku (垂迹), literally, a "trace") of Buddhist deities (the honji (本地), literally, "original ground").[1][3] The two entities form an indivisible whole called gongen and in theory should have equal standing, but this was not always the case.[4] In the early Nara period, for example, the honji was considered more important and only later did the two come to be regarded as equals.[4] During the late Kamakura period it was proposed that the kami were the original deities and the buddhas their manifestations (see the Inverted honji suijaku section below).[4]
The theory was never systematized but was nonetheless very pervasive and very influential.[1] It is considered the keystone of the shinbutsu-shūgō (syncretism of Buddhist deities and Japanese kami) edifice.[5] Honji suijaku has often been seen as similar to interpretatio Romana, a mode of comparison promoted in antiquity by scholars such as Tacitus who argued that barbarian gods were just the foreign manifestations of Roman or Greek deities.[6]
The term honji suijaku itself is an example of the Japanese practice of Yojijukugo, a four-character combination of phrases which can be read literally or idiomatically.