In his writings Saichō frequently mentioned traditional Tendai classifications of Buddhist doctrine, such as the division of the Buddha’s teaching into five periods and eight types of teaching (goji hakkyō). In addition, he developed a number of new systems of classification which were designed to reveal various aspects of the superiority of Tendai teachings over those of other schools. Even before studying in China, Saichō had divided Buddhist schools into two categories, those based on sūtras (the words of the Buddha) and those based on Sāstras (works by Buddhist monks). Using this classification, Saichō criticized the two preeminent Buddhist schools in Japan, the Hossō and Sanron, because they were based on works (sāstras) by Buddhist monks rather than on the words of the Buddha. Twenty years later in the Hokke shūku he further refined this system by dividing the schools based on sūtras into two groups: the Tendai School, which was based on the Lotus Sūtra, and all other schools based on sūtras, such as the Kegon School.