The concept of neixun ziwu was developed by Zhanran. Zhiyi taught that the Lotus Sutra is transmitted eternally from buddha to buddha. Addressing theoretical problems posed by the Lotus Sutra having no origin in an infinite past, Zhanran proposed the existence of a first buddha. There was, however, no doctrinal basis for a first buddha. Zhanran thus determined that there was a period of “no teaching” during which the first buddha became enlightened due to his own “internal perfuming” (neixun), instead of through coming under the influence of the teachings of a previous buddha. He used this term neixun exclusively for discussing the enlightenment of the first buddha.
Subsequent masters of Chinese Tiantai and Japanese Tendai doctrine developed two interpretations of Zhanran's theory. One camp believed the notion of a first buddha to be factual and the other claimed it to be hypothetical. Many Song dynasty masters such as Zhili, Yuanqing, and Shanyue took Zhanran's theory at face value, while Japanese (predominately) Tendai masters such as Genshin, Kakucho, and Shoshin proclaimed it hypothetical. They raised two main objections to Zhanran's theory. First, they questioned whether it is possible to seek for a beginning of Buddhism. Second, they argued that the postulation of “no teaching” precludes the cause for becoming a buddha and that, without that cause, this explanation resembles heretical, non-Buddhist teachings. Genshin questioned Zhili's approach to this problem, and many Japanese Tendai masters agreed with Genshin's interpretation.