Court noble law (公家法)
Court noble law is a legal system that was valid in the court noble society between the Heian period and the Edo period.
Succession of ritsuryo law
Governmental regulations of Imperial Court in the medieval period was basically a succession of provisions of ryo (administrative code) in the system of the Japanese nation under the ritsuryo codes, and it seems that there was no profound structural change on the face. However, due to changes of the court noble society itself, significantly different features from the system of the Japanese nation under the ritsuryo codes can be seen in its structure and in practical operation.
Hereditary social structure
Under the ritsuryo system, the structure of the court noble society was determined by clarifying rank order and official duties of each government official based on job grades and Ikai (Court ranks). While this system was to define disparity of positions between government officials who are in the noble class and the other commoners who are in the subordinate class, it was, at the same time, to determine one's role based on meritocracy, and did not have hereditary law structure inherently.
(For more information, see ritsuryo system and ritsuryo law.)
However, as disparity of positions within government officials became wider and government officials became to be supplied from certain clans by heredity, not by meritocracy as intended by the ritsuryo system, roles of government officials became to be determined by the family lines to which they belonged and role of each family line became specialized. These family lines respectively accumulated practical disciplines such as 'karei' (family customs) and 'shoshi rei' (officials customs) and became highly specialized, and in the medieval period, they assumed certain job grades almost by heredity.
Such heredity system through reigns of the family was also seen within the Imperial Family, and Insei (rule by the retired Emperor), which intermittently continued from the retired Emperor Shirakawa until the Muromachi period for form's sake, can be seen as heredity of household management within the Imperial Family.
(For more information, see Cloister government and Chiten no kimi [the retired emperor in power].)
Formation of Ryoge no kan (posts outside the original ritsuryo code created by Imperial edicts)
Another fundamental change in the ritsuryo system in the medieval period was formation of so-called ryoge no kan such as kebiishi (officials with judicial and police powers). The feature of this ryoge no kan was that the officials could process government affairs for which they were responsible all on their own. In the original ritsuryo system, governmental affairs were processed in order, from the upper rank, following the line of governance, so departments near the bottom of the bureaucratic organization merely did paperwork, and their decision-making was ultimately done by the emperor through upper organizations. However, ryoge no kan such as kebiishi were able to process one government affair in a cross-sectoral manner beyond the line of governance of organizations under the ritsuryo codes and therefore able to promptly make settlements beyond rules of traditional Japanese nation under the ritsuryo codes, so they were able to perform certain governmental affairs on their own without following minute procedures due to complicated bureaucratic organization under the ritsuryo codes. In fact, Kebiishi cho (Office of Police and Judicial Chief) was excellent practically, so later, it expanded its territory of duty by eating away traditional organizations of government according to the ritsuryo codes. It can be said that such formation of ryoge no kan brought about a significant change in the ritsuryo system.
For negotiation between such ryoge no kan and organizations of government according to the ritsuryo codes basically had to be done by accumulation through customs because there was no clear stipulation in the existing ritsuryo codes. In the medieval period when ryoge no kan formed widely, families called Myobo-ke (scholars of the law) with a duty of lawyers emerged responding such realistic demands to reinforce legal aspects of practical governmental affairs by checking them against stipulations of ritsuryo codes. Such Myobo-ke were also formed by establishing heredity of the position of Myobo hakase who were originally instructors of Myobodo (study of ritsuryo codes) in Daigaku-ryo (Bureau of Education under the ritsuryo system) by changing Myobodo to hereditary learning. One example that emergence of medieval hereditary lineage of duties such as Myobo-ke and formation of ryoge no kan closely influence each other is the process in which the function of Gyobusho (Ministry of Justice) to determine appropriate punishment was lost as jurisdiction of kebiishi expanded and it became common for Myobo-ke to recommend charges. In addition, while such Myobo kanmon (written reports to the Imperial Court) by Myobo-ke referenced ritsuryo law, the choices were pretty arbitrary, and it is worthy of attention that ritsuryo provisions did not directly have normative influence in the medieval period. In the medieval period, local rules of individual families often had a priority over ritsuryo law, and accumulation of negotiations between families became government affairs. Accumulation of practices in each field was eventually compiled in a manual as manners and ancient practices, and it is worthy of attention that what was legally meaningful and what was not were not strictly segmented.
It is reasonable to consider that ritsuryo law remained in a relative position in the context of rich operation of law in the medieval period.
Aspect as common law
For formation of the court noble law that is distinguished from ritsuryo law, cloister government that was started by the retired Emperor Shirakawa can be pointed out as a direct and significant momentum. Of course, formation of ryoge no kan dates as early as the ninth century and reorganization within nobles continued through regency, and a qualitative shift of ritsuryo system was going along slowly but steadily before cloister governments. It can be said that during the period of cloister governments the Imperial Family also started to have household management of its own although issues of political history related to formation of cloister governments are not the subject we deal here. Separate from the inner Court of the emperor, In no cho (Retired Emperor's Office) was established under retired emperors and cloistered emperors, which treated internal government affairs just like Mandokoro (Administrative Board) of sekkan-ke (the families which produced regents). What's important here is that In no cho and Mandokoro handled only their internal government affairs respectively, and neither of them directly handled general government affairs, but negotiation between them made up government affairs of the court noble society.
While Dajokan (Grand Council of State) handled government affairs under provisions of ritsuryo law in the ritsuryo system, accumulation of individual negotiation processes and cases served as provisions in doing government affairs in medieval period and such accumulation was the legal basis. Therefore, it can be pointed out that the court noble law in the medieval period had strong nature of common law.