The Southern school of Zen had based itself on the Nirvana Sutra, which says, “That which lacks Buddha nature is deemed an insentient thing”, and its teachers argued that, if insentient phenomena lack Buddha nature, they could not teach the Dharma. However, Tozan knew that the Northern school and the fourth and fifth Ancestors had asserted that inanimate phenomena do expound the Dharma. In his own time, the National Teacher Nan’yo Echu (d. 775) argued the case. It was not without ancient authority. In the fifth century, Dao Sheng, an influential Buddhist teacher, and a disciple of the great translator Kumarajiva, had argued from the Mahaparanirvana Sutra, that if all sentient beings could become Buddha then so too could mountains. He was reviled for this understanding and forced to withdraw into the wilderness, where he was said to have expounded the Dharma to the lifeless rocks that nodded their heads in responsive understanding.