The doctrine of innate enlightenment was developed in China out of the Buddha-nature doctrine. It is first mentioned in the Awakening of Faith in the Mahayana scripture. According to Jacqueline Stone, The awakening of faith in the Mahayana sees original enlightenment as "true suchness considered under the aspect of conventional deluded consciousness and thus denotes the potential for enlightenment in unenlightened beings." In medieval China, the doctrine developed from the Huayan school and also influenced Chan Buddhism. The doctrine is also a common theme of the Platform Sutra of Huineng and was taught by Chinese Chan masters as "seeing original nature". Inherent enlightenment was often associated with the teachings of sudden enlightenment and contrasted with the "gradual" approach and the idea of “acquired enlightenment” or shikaku. The first Japanese to write of this doctrine was Kūkai, founder of Shingon Buddhism.
The doctrine of innate enlightenment was very influential in Tendai from the cloistered rule era through the Edo period. The Tendai view of hongaku saw it as encompassing not only all sentient beings, but all living things and all nature, even inanimate objects - all were considered to be Buddha. This also includes all our actions and thoughts, even our deluded thoughts, as expressions of our innately enlightened nature. Tamura Yoshirõ saw original enlightenment thought as being defined by two major philosophical elements. One was a radical non-dualism, in which everything was seen as empty and interconnected, so that the differences between ordinary person and Buddha and all other distinctions, were ontologically negated. The other feature of hongaku was the affirmation of the phenomenal world as an expression of the nondual realm of Buddha nature. This was expressed in phrases such as “the worldly passions are precisely enlightenment” and “birth and death are precisely nirvana.” The Tendai doctrine of hongaku had deep impact on the development of New Kamakura Buddhism, for many of those who founded new Kamakura Buddhist schools studied Tendai at Mount Hiei. During the 1980s a Japanese movement known as Critical Buddhism has attacked original enlightenment as an ideology that supports the status quo and legitimates social injustice by accepting all things as they are as expressions of original Buddha nature.
