Myohodo is a department of Daigakuryo, an educational institution under the system of centralized administration established under the ritsuryo legal codes in ancient Japan, where the ritsuryo legal codes (the study of law) was taught.
Under Taiho Code, there were no system to develop the government posts and specialists handling the interpretation of ritsuryo and in Daigakuryo there seemed to be two subjects at first - future Myogyodo as the main course and Sando, a subject of mathematics. The interpretation of ritsuryo was handled mainly by people from China called Ryoshi, experts who probably also cultivated future Ryoshi privately. It is because in China, the native land of ritsuryo, only Confucianism (=Myogyodo) was recognized as the study of worthy men and the other studies including law were recognized as Hogi which were regarded as less worthy and the ritsuryo legal codes in Japan were affected by such a trend.
Later doctors of Ritsugaku were appointed together with doctors of Monjodo, a department of Chinese poetry and history on the need to cultivate experts of ritsuryo by ordinance on September 3, 728. After two years, on April 22, 730, 10 students of Myoho were taken and the department was established. The ordinance at that time stated to take the students of Monjo and Myoho from the children of Zonin officials and Hakucho people, therefore the children of lower-level officials of the central and local governments or common people became the Myoho students and it was seen as a lower ranking department than Myogyodo which took students from the children of aristocrats. Soon after the Myoho students were taken (it is unclear when), the doctor of Ritsugaku was renamed the doctor of Myoho.
The text book of Myohodo was ritsuryo itself and those who could answer 8 questions out of 7 from Ritsu and 3 from Ryo passed the exam. Those who answered all correctly (Kodai) were appointed as superior Daishoi rank and 8 or 9 questions correctly (Otudai) were appointed as inferior Daishoi rank. Because the examination of Myohodo was difficult, in 813 unsuccessful applicants were still allowed to have the qualification to be appointed as Kunihakase (a teacher of local institute). Details of the lectures and whether or not Kakushiki (ordinances) and Kanpu (government documents) etc. were studied to complement ritsuryo are unclear.
In the Heian period, in the restructuring policy of ritsuryo by the Emperor Kanmu, doctors of Myoho were appointed also in Dazaifu (the local government institution in Kyushu) in 799 and a measure was taken to increase the students of Myoho from 10 to 20 by cutting 10 of the fixed 30 students of Sando in 802. Also after the transfer of the capital to Heian-kyo, Myohodoin, a facility for the Myoho students to take lectures and boards was constructed including the central school building and east/west dormitories on the southernmost side of Daigakuryo. It is considered that there were also such facilities in Heijokyo (a previous capital), but Myohoin in Heiankyo was likely the same size as Myogyodoin (written in "Daidairizu Kosho"), which indicated the position of Myohodo was getting higher at that time.
In the early 9th century, the study of ritsuryo flourished and a lot of Myoho experts were produced including SANUKI no Naganao, OKIHARA no Miniku, NUKATA no Imatari, KOREMUNE no Naomoto and also clans of Myoho doctors for generations were produced including Sanuki (future Wake clan) and Koremune (future Yoshimune clan)
Though there remain no books by Myoho experts of this time, their theories (called 'Sanki' or 'Kekki') were quoted in books such as "Ryonogige", "Ryonoshuge" and transmitted to the present time.
However, in the mid Heian period, Kidendo, a Monjo subject, exceeded the other departments, therefore Myohodo was positioned lower than Kidendo and declined temporarily. Though the system under the ritsuryo legal codes declined, minimum social order was sought, which required Myoho experts as the specialists of law in the field of order and justice and government officials who had studied Myohodo were sent to the ministries such as Gyobusho, Danjodai, Kebiishi. Also Myoho students were appointed as lower rank officials by the recommendation systems such as Dokyo and Donenkyo. In the 10th century, the position of Gyobusho declined and the jurisdictions of robbery and counterfeit coinage were transferred to Kebiishi and the other crimes were transferred to Daijokan. Especially in Daijokan, when officials of lower than grade five committed a crime, a Jinnosadame (council) called 'Zaimyosadame' was held where the emperors or Kugyo (ministers) with lower positions than Sekkan (regent) who did not know ritsuryo very well, asked opinions to the doctors of Myoho and Myoho experts for submission of Myobokanmon response papers. While government systems were created away from the existing ritsuryo system such as regency, Kebiishi and Myoden land control system, Myoho experts were expected to interpret those as legal systems in ritsuryo because the government was losing its power to create a new law system at that time. It was in such a period that KOREMUNE no Tadasuke compiled "Seiji Yoryoku" in about 1002.
In the period of Insei (rule by a retired emperor), Myohodo flourished again in response to increasing cases about land possession and buying, selling, loan and growing security concerns. The doctors of Myoho became so active that they submitted Myobokanmon response papers not only to the emperors and Daijokan (government's supreme organ) but also to Chitennokimi (a retired emperor) and Innocho (administrative organization of retired emperor). On the other hand, there were problems caused by hereditary transfers of doctors of Myoho developed by Sakanoue and Nakahara clans, by which some doctors of Myoho made bad Kanmon response papers with apparently wrong interpretations of law, which future scholars could find. But on the other hand, some great Myoho experts wrote books such as "Hoso Shiyosho" by SAKANOUE no Akikane, "Saiban Shiyosho" by SAKANOUE no Akimoto (a grandchild of Akikane), "Myoho Jojokanroku" by NAKAHARA no Norisumi, "Kingyoku Shochusho" by NAKAHARA no Norito etc. In the late Heian period, after Daigakuryo was eliminated, the department of Myohodo practically disappeared and the doctors gave lectures of ritsuryo in their private schools. On the other hand, after so called Kugeho (law of court nobles' society) was established, Myoho experts including the doctors of Myoho participated in the council because the law was based on the low interpretations of Myoho experts and Myobokanmon.
Also OE no Hiromoto who became an adopted son of Nakahara clan to study Myohodo, was likely to have something to do with the establishment of Myohodo and Bukeho (the low system of samurai society) because he participated deeply in the establishment of the Kamakura bakufu and influenced "Goseibaishikimoku (the law of samurai regime)" of the legal book "Saiban Shiyosho. "
However, after the period of the Northern and Southern Courts (Japan), the Muromachi bakufu dominated Kyoto and took over the government function of the Imperial Court and Innocho, and Myohodo became a mere name and survived only as a study of historical precedents.