Tendai Sect (天台宗)
Tendai Sect is a sect of Mahayana (greater vehicle) Buddhism. Its fundamental sutra is Lotus Sutra. It originated in China and was introduced into Japan by Saicho in the early Heian period.
Chinese Tendai Sect
Its first and second founder was Emon of Hokusei and Kozan Eshi (515 - 577) respectively and Chigi was Eshi's disciple (it is also said that the 1st founder was Ryuju, the 2nd was Emon, the 3rd was Eshi and the 4th was Chigi)
Chigi was a scholar priest who originated a doctrine based on Hokke-kyo sutra, Makahannya haramikyo sutra and Daichidoron (Commentary on the Great Wisdom Sutra) that were translated by Kumaraju as well as Nehangyo sutra, advocated Kyoso hanjaku (theory on the history of sutra establishment) based on Goji hakkyo, which deems Hoke-kyo sutra as paramount, and preached to become Buddha through shikan (Tendai Meditation).
However, there are views asserting 'Hoke-kyo sutra translated by Kumaraju is substantially different from the existent Sanskrit version and in particular, Hobenbon daini, which Tendai Sect emphasizes might have been modified based on Kumaraju's own doctrine.'
In view of the fact that Kumaraju attached importance to Hoke-kyo sutra, Makahannya haramikyo sutra and Daichidoron, it can be said that the foundation of the Tendai Sect was triggered by Kumaraju.
After its basis was established at Mt. Tendai, it absorbed the Nehan Sect and the Tendai Sect was finally established. Chigi's Hokke gengi (Essentials of the Lotus Sutra), Hokke mongu (Commentary on the Lotus Sutra) and Makashikan (Mahayana Practice of Cessation and Contemplation) are collectively called Sandaibu (the three important scriptures) and are deemed as the essence of Tendai Sect Buddhism. Shoan Kanjo (561 - 632), 4th founder, recorded and compiled these writings by Chigi. After Kanjo, the sect was succeeded by Chii (? - 680), Kanjo's disciple, followed by Ei (634 - 713), Chii's disciple, and Sakei Genro(673 - 754). As the influence of Tendai Sect declined after Kansho, Sakei Genro is assumed as the 5th founder.
Keikei Tannen, 6th founder, who was a disciple of Genro and is deemed as the beginner of the restoration of Tendai Sect, wrote many books concerning the doctrine of the Tendai Sect, including Sandaibu.
Japanese Tendai Sect
Its official name is the Tendai Hokke En Sect. Sometimes it is called the Hokke En Sect, Tendai Hokke Sect or simply Hokke Sect. However, the last one is seldom used because it could be confused with Hokke Sect of Nichiren kyogaku (religious doctrine advocated by Nichiren). The writings related to the Tendai Sect were initially brought into Japan by Ganjin Wajo, who was a priest of the Ritsu Sect as well as the Tendai Sect. Then, Denkyo daishi Saicho (767 - 822) traveled to Tang (805), visited Mt. Tendai, learned the doctrine of the Tendai Sect, returned to Japan (806) and founded the Japanese Tendai Sect.
At that time, Nanto rokushu (the six sects of Buddhism which flourished in ancient Nara), such as the Hosso Sect and the Kegon Sect, had already been introduced into Japan, but in China, they were the sects that were founded later than Tendai Sect. After returning to Japan, Saicho came back to Enryaku-ji Temple on Mt. Hiei and since then, he nurtured many Buddhist monks including Ennin and Enchin. As Saicho advocated the doctrine of Hokke ichijo which asserted all people were able to become Buddha, disputes arose between Nara Buddhism (Nanto rokushu) which stuck to the position of Theravada Buddhism. In particular, the debate conducted between the Tokuitsu of the Hosso Sect is well-known. His innovative initiatives to establish Daijo kaidan, recognize monks who received Daijokai (the commandment of Mahayana Buddhism) as Tendai Sect monks and train them as Bosatsuso (priests of Mahayana Buddhism) by containing them in Mt. Hiei for 12 years deepened the confrontation between Nara Buddhism, which monopolized, due to vested interests, and Kaidan-in which were authorized to grant Shojokai (commandments of Theravada Buddhism) brought by Ganjin Wajo. As Daijokai was deemed at that time as commandments for secular people, not for Buddhist monks (even at present, Daijokai is not recognized as Buddhist precepts under Theravada Buddhism, such as Sri Lanka Theravada Buddhism), the refutation by Nanto (Nara) priests might be reasonable in light of the common sense that then prevailed. As a result of disputes, imperial sanction concerning Daijo kaidan was given after Saicho's death and the Tendai Sect was formally established, both in name and substance, as an independent religious sect.
Tendai Esoteric Buddhism (Taimitsu)
While Mikkyo of the Shingon Sect is called Tomitsu, that of the Tendai sect is called Taimitsu. Religious sects that deem Nichiren to be the real Buddha in the Mappo era criticize the current Japanese Tendai Sect asserting that it is close to the Shingon Sect because it has substantially incorporated the elements of Esoteric Buddhism and the teaching of Mt. Hiei was distorted by Ennin and Enchin because they incorporated Shingon Esoteric Buddhism after Saicho's death and against his will. In considering the above, however, several points, including historical situation, should be taken into account.
When Tendai daishi Chigi, who is said to be the founder of Tendai Sect in China, advocated Kyoso hanjaku (also called Kyohan for short) based on Goji hakkyo, in which he systemized Buddhism as a whole according to the doctrine of Hokke-kyo sutra, Esoteric Buddhism had not yet been introduced and therefore, it was not included in Kyohan.
However, Esoteric Buddhism, the latest Buddhism at the time, had already been introduced when Denkyo daishi Saicho, the founder of the Japanese Tendai sect, traveled to Tang. As Saicho worried that Japanese Esoteric Buddhism was imperfect, he received Kanjo (a ceremony to be the successor) of Esoteric Buddhism from Jungyo and returned to Japan with the intention of systemizing Buddhism as a whole, including Esoteric Buddhism. When Kukai returned from Tang one year later after Saicho had returned, Saicho recognized that the Esoteric Buddhism he had learned in Tang from Jungyo was collateral and asked Kukai with the utmost courtesy to take him in as a disciple in order to study Esoteric Buddhism, but he eventually parted from Kukai due to their differences in views on Buddhism. Due to the above, incorporation of perfect Esoteric Buddhism into Tendai kyogaku was stopped.
However, there is no doubt about the fact that Saicho intended to establish the doctrine of comprehensive Buddhism by integrating Buddhist precepts based on Hokke-kyo sutra, Zen, Nenbutsu (Buddhist prayer) and Esoteric Buddhism and his disciples, including Ennin and Enchin, succeeded Saicho's will, restudied Esoteric Buddhism and completed Tendai kyogaku which had been the earnest desire of Saicho. Therefore, it can be said that the origin of the current Tendai Esoteric Buddhism is not Ennin and Enchin but Saicho himself. Further, as Enchin pointed out 5 defects in Kukai's 'Jujushinron' (Ten Stages of Mind Development) and refuted it as 'there is no superiority or inferiority between Tendai and Shingon,' the views held by sects which deem Nichiren to be the real Buddha that Ennin and Enchin distorted Tendai by incorporating Shingon Esoteric Buddhism, is completely denied by the above fact.
The difference between Shingon Esoteric Buddhism (Tomitsu) and Tendai Esoteric Buddhism (Taimitsu) is that while Tomitsu advocates its doctrine with Dainichi nyorai being its principal image, Taimitsu takes the stance of Hokke ichijo with Shakamunibutsu of Kuon-jitsujo (eternal life of the Buddha), which is the principal image of Hokke-kyo sutra, being its principal image.
Shishu kengaku (learning the four sects)
In view of the above-mentioned, it is pointed out that the Japanese Tendai Sect founded by Saicho is, in spite of the same name, a different one from the Chinese Tendai Sect which is based on Hokke-kyo sutra and founded by Chigi, and although it succeeds Chigi's doctrine and is based on Hokke-kyo sutra, it is a unique one that tried to fuse the elements of Zen, Buddhist precepts, nenbutsu and Esoteric Buddhism or the one that tried to develop Chigi's Tendai kyogaku while succeeding it. Therefore, Enryaku-ji Temple is also called dojo (a hall used for training) for Shishu kengaku.
Ascetic training of the Tendai Sect emphasizes 'Shikan,' which is based on Hokke-kyo sutra and could be said to be Hokke Zen. Ascetic training of the current Japanese Tendai Sect can be summarized in the words of "asa daimoku, yu nenbutsu" (read the Lotus Sutra in the morning and pray to Amida Buddha in the evening). In the morning, Buddhist monks practice daimoku, namely gyoho of chanting Hokke-kyo sutra (it is called hokke senbo) and in the evening, they practice gyoho of praying to a principal image Amida Buddha (it is called reiji saho).
Shikangyo developed further in later years and became the first step of the development of new Buddhism called 'nenbutsu.'
The sect strengthened its basis by conducting incantation of Tendai Esoteric Buddhism (Taimitsu) and becoming comprehensive Buddhism (there is doubt and criticism concerning the reason why the sect needed to conduct nenbutsu and/or incantation if it believed the doctrine of Hokke-kyo sutra was right). Furthermore, in later years, the sect established the Tendai hongaku philosophy, which asserts that Buddhist nature dwells in all beings. As the sect played a leading role in the education of Buddhism in Japan, many scholar monks who advocated new religious sect doctrines, such as the Yuzu Nenbutsu Sect, the Jodo Sect, the Jodo-Shin Sect, the Rinzai Sect, the Soto Sect and the Nichiren Sect, were turned out from the sect from the end of Heian period to Kamakura period.