Esan kiitsu (会三帰一)
Esan kiitsu (Esan kiichi) means that learning ichijo (Single Vehicle) through understanding sanjo (the Three Vehicles carrying sentient beings to the world of enlightenment). It is also called kaisan kenichi or sansokuichi.
Summary
It is an interpretation created by the Tendai sect, but is quoted in different sects such as schools in the Nichiren sect.
Sanjo indicates three teachings told for shomon (or shomon-jo, vehicle of the hearers), engaku (or engaku-jo, solitary-buddha vehicle), and bosatsu (or bosatsu-jo, enlightenment-bound vehicle). Ichijo means a teaching to become the only Buddha.
Shakuson (Shakyamuni) made various preachings during his life of 40 years, which can be summarized into three: for shomon, engaku, and bosatsu. In other words, he preached shomon for people who were seeking it, engaku for people who were seeking it, and bosatsu for people who were seeking it; he made different types of preaching's to different people. This is called Sanjo kakubetsu.
In the Muryo gikyo (Sutra of Immeasurable Meanings), which is a Kai-kyo (sutra read before the main sutra) of the Lotus Sutra, there is a description which says 四十余年未顕真実. It means that the preaching Shakuson made in his life of 40 years still does not present the truth, and those preachings became hobenbon (the way to attain the enlightenment), and had been made temporarily as just a way of guiding all living things.
It was revealed that, therefore, the preaching of sanjo was a way to preach ichijo. This is called esan kiitsu or kaisan kenichi.
In the first half of the hobenbon in the Lotus Sutra, Junyoze (Buddhism Ten Factors of Life) was preached and sanjo was briefly established, and then the preaching of ichijo was made. This is called Ryakkaisan kenichi. Sanjo was established with a wide range through doctrine, hiyu (analogy), or fate from the latter half of Hobenbon chapter two through gakumugakuninkihon chapter nine. This is called Kokaisan kenichi.
Criticism and development
As stated above, esan kiitsu was created by the Tendai sect, which regards the Lotus Sutra as the highest, and was adopted by various schools in the Nichiren sect. However, there is an opposing opinion.
First of all, the Hosso sect preached goshokakubetsu (five natures distinction) based on the Gejinmitsu-kyo Sutra, and established a theory that there are distinctions among the people and not everyone is soon able to become a Buddha. This triggered a controversy with the Tendai sect. It is so-called San-ichi Gonjitsu (debate over One-provisional and three-true teaching vehicles) between Tokuitsu and Saicho. In the Tendai sect, it is said that a disciple of Saicho cut off the argument claiming that Saicho outdebated Tokuitsu's theory (it is to note that the Kegon sect joined the controversy and denied the goshokakubetsu based on the doctrine of Sendaijobutsu in the Nehan-gyo Sutra [The Sutra of The Great Nirvana], and agreed to the Ichijo-jobutsu).
Also, in each school of Hokke Sect, it is believed that the Lotus Sutra preaches esan kiitsu. However, in Buddhist Studies, it is pointed out that there is not much of a basis behind the esan kiitsu because although the Lotus Sutra set a goal of 'learning ichijo through understanding sanjo,' it is not clearly explained how these different people can be treated equally in accordance with the preaching of ichijo, in addition to the fact that there is an academic theory that the Lotus Sutra has no content. It is also pointed out that actually Nehangyo rather than Lotus Sutra explains the bussho josho (one of the Buddhist teachings about the status of reaching the Nirvana and its eternity) of sanjo as well as the logical reason of esankiitsu ("Bukkyo fukyo taikei" and so on).