Fukai-no-Joten Fukaijoten (Irreversible Permanent Code Irreversible Eternal Code) (不改常典)

Fukai-no-Joten/ Fukaijoten (Irreversible Permanent Code/ Irreversible Eternal Code) is a law frequently referred to in the enthronement address of Japanese successive emperors since the year 707, and is said to have been established by Emperor Tenchi (his name is also pronounced "Tenji"). Based on the words of Emperor Tenchi that says 'the law established and promulgated as a permanent code that should not be irreversible,' it is referred as Fukai-no-Joten/ Fukaijoten (Irreversible Permanent Code/ Ireversible Eternal Code) in academic society.

This code was not correctively compiled in the "Nihonshoki" (Chronicles of Japan), but appeared as a reference in the words of the posterity emperors after "Shoku-Nihongi" (Chronicles of Japan II). The first reference to the code appeared in the imperial edict Empress Genmei, and since then, the code was cited frequently until the Edo period. Although in historical materials, there is no specific citation to the contents of the code, it is positioned as an extremely important law, and attracts the attention of historians. There are numerous theories about the origin of the contents, including the direct line imperial succession code theory, which advocates that it is a code for transcending the Imperial Throne from father to son, and there is no established theory.

Summary

Fukai-no-Joten/ Fukaijoten' is not its formal name, but a historical term derived from one phrase used in the imperial edicts upon enthronement.
In the edicts after Emperor Kanmu, the words 'Fukai-no-Joten/ Fukaijoten' is not found, but cited as 'the law that Emperor Tenchi established for the first time.'
As a historical term, both are understood as Fukai-no-Joten/ Fukaijoten.

There is no citation for this code in the section about Emperor Tenchi of "Nihonshoki," but there are in various written materials referring to the edicts of the emperors after the period of 'Nihonshoki.'
It was first cited in the imperial edict upon enthronement of Empress Gensho, and since then, it is exclusively found in the imperial edicts upon enthronement of the successive emperors or in the form of reference to an imperial edict upon abdication of a certain former emperor used in the imperial edict upon enthronement of the successor. However, not all of the imperial edicts upon enthronement touch Fukai-no-Joten/ Fukaijoten. No edict presents a concrete content, but touches it in a context such as; the former emperor's enthronement and its reign is endorsed by Fukai-no-Joten/ Fukaijoten, the Imperial Throne should be handed down according to Fukai-no-Joten/ Fukaijoten, or the Imperial Throne should be ascended according to the law established by Emperor Tenchi.

Fukai-no-Joten/ Fukaijoten had been considered as the laws formulated in the Taika Reforms or Omi-Ryo (Omi Administrative Code), from the Edo period to the first half of the 20th century, however at present this theory is not supported. The most widely-accepted theory is the direct line imperial succession code theory that Koyata IWASAKI presented in 1951 in his article 'The permanent code established by his majesty Emperor Tenchi,' in which he argues that this is the law that determinates the imperial succession rule, eliminating collateral successions between brothers. Since then, corrections, criticisms, and the presentation of new theories have been successively presented to date, and still various theories are argued. Among the other imperial succession theories, the theory of lineal descendent hereditary imperial succession law theory, in which the throne is exclusively ascended to the son born from the legal wife, that of the throne abdication law, which establishes the succession of the throne by abdication, and the crown prince theory, in which the succession is undertaken by pointing the crown prince, can be found. Among the theories that argue the code's indifference with the imperial succession, a theory that it is a law to establish the regent of the Fujiwara clan, theory that it is a law to establish an imperial autocrat similar to that of the emperors in the Sui and Tang periods, and the theory that it is a norm that establishes the imperial family's successive rule, can be found.

In addition, there are interpretations made based on the combination of various theories by period, in which a wide range of theories are found, from the theory that insists on the existence of another totally different law to the theory that argues that it is a law which had gradually became a dead letter. Another is the pretext theory that presents a hypothesis that Fukai-no-Joten/ Fukaijoten was not established by Emperor Tenchi, but it was posteriorly written under the pretense that it was set up by Emperor Tenchi. Although the theories surrounding Fukai-no-Joten/ Fukaijoten are mere direct interpretation of a paragraph of imperial edicts, they can lead us to different views on the political system during that period and its transition.

Code of the Taika Reforms theory - by Norinaga MOTOORI

Omi-Ryo theory - argued by Hiroyuki MIURA and Masajiro TAKIKAWA, and also a popular theory accepted since the Meiji period to the 1940's.

Theory arguing that it is Omi-Ryo, but only during the period of Emperor Kanmu or later - by Shohachi HAYAKAWA

Code of imperial succession theory - the most dominant theory since the 1950's.

The direct line imperial succession code theory - by Koyata IWASAKI, Shigeo KITAYAMA, Kojiro NAOKI, and Ken SHINOKAWA.

The legitimate child imperial succession code theory - by Mitsusada INOUE

The code of imperial succession by abdication theory - by Yasuhiko KURAZUMI

The crown prince succession system theory - by Tei MORITA

The Emperor's family and the Fujiwara clan joint administration and assisted government regime theory - by Encho TAMURA

The Sui-Tang style imperial autocrat theory - by Ryutaro MIZUNO

The general principle of the imperial reign theory - by Takashi TANAKA

Form of Sokui no Mikotonori (imperial edict upon enthronement) and Fukai-no-Joten/ Fukaijoten

The imperial edicts at the enthronement of Empress Jito or before are not documented. For the imperial edict upon enthronement available at present, there exist only a part of the edicts of Emperor Monmu and his successive emperors in the later time, archived in "Shoku-Nihongi" (Chronicles of Japan II), and except for some cases, they are written in Senmyo (imperial edict) texts. The first reference to Fukai-no-Joten/ Fukaijoten is found in the imperial edict upon enthronement of Emperor Genmei, successor of Emperor Monmu. Among the imperial edicts upon enthronement, some of them have no reference to Fukai-no-Joten/ Fukaijoten, and therefore, many emperors' edicts are not documented today. However, around at the Heian period, the citation to the code (in the edict) was established as a rule, and it had been practiced until the Edo period.

There are two methods of citation depending upon the period. The words 'Fukai-no-Joten' can be only found until the imperial edict upon enthronement of Empress Koken. This word in Chinese characters is suffixed with Kana in some cases and this means that originally the word should not be read in the Chinese-style (On-Yomi).
The word 'Fukai-no-Joten/ Fukaijoten' is not the name of the code itself, but the word extracted by present scholars from a part of a long adjective phrase qualifying a certain code whose name is not mentioned, as follows: '[the code] that His majesty Oyamatoneko no Sumera Mikoto (referring to an emperor), who resides in the highly respectable and noble Omi-no-Otsu-no-Miya Palace, established as the irreversible and eternal code, which should not be modified as long as the universe exists and as eternal as the sun and the moon shed light.'
In the imperial edicts upon enthronement of Emperor Kanmu and later, it is mentioned as the law that Emperor Tenchi established for the first time, but the adjective phrase, 'which should not be modified,' is omitted.

The argument that the name and form of Fukai-no-Joten/ Fukaijoten do not follow the requisites of Ritsuryo (the legal codes of the Nara and Heian periods) itself can be developed as an independent theme of one article. According to the popular theories, it had no established form and it seems to have been transferred verbally, however, there are such theories that advocate: i) it was equipped with a refined form comparable to Ritsuryo, ii) it was handed down from one emperor to another in a confidential manor, and iii) it might have been a vague norm that permitted a wide range of interpretation.

The law established and promulgated as the permanent code - cited by Empress Genmei, Emperor Shomu, and Empress Koken.

The code first conceived and established - cited by Emperor Kanmu, Emperor Junna, Emperor Ninmyo, Emperor Seiwa, Emperor Yozei, Emperor Koko, Emperor Gosanjo, Emperor Antoku, Emperor Shijo, Emperor Gokashiwabara, and Emperor Nakamikado.

Imperial edict upon enthronement of Empress Genmei

The first appearance in the materials is found in the imperial edict upon enthronement of Empress Genmei dated on August 22, 707, compiled in the "Shoku-Nihongi" (Chronicles of Japan II), and the reference to Fukai-no-Joten/ Fukaijoten appears in two places.

Genmei, first explains the situation at the time of the enthronement of late Emperor Monmu. Emperor Monmu is a son of Prince Kusakabe, and after his enthronement, he ruled in power shared with Emperor Jito.
Genmei says that this was done based on 'the code which should not be modified as long as the universe exists and as long as the sun and the moon shed light.'

In continuation, Genmei expresses his intention to undertake the governance of the nation (Osukuni amenoshita no matsurikoto) counting on the assistance of her grand ministers and hundreds of officials and states "to hand down the reign by securing the lay of the nation's governance, which is also irreversible like the universe and deemed as the permanent code, without decline nor oscillation.'

During the period mentioned in this edict, the throne was handed down from Emperor Jito to Emperor Monmu and then Empress Genmei. Monmu is a son of Prince Kusakabe and a grand son of Emperor Tenmu. Jito as well as Genmei are empresses, and Jito is Monmu's grandmother and Genmei is Monmu's mother. Therefore, Fukai-no-Joten/ Fukaijoten mentioned in the former part is the law that justifies the succession of the throne from the grandmother to the grandchild and their shared rule, while Fukai-no-Joten/ Fukaijoten mentioned in the latter part are noted as the law of the nation's governance, and is used in a context in which the empress wishes it's effect to continue.

Imperial edict of the enthronement of Emperor Shomu

The following historical material is the imperial edict issued upon enthronement of Emperor Shomu, which can also be found in the 'Shoku-Nihongi' (Chronicles of Japan II). Accordingly, when Empress Genmyo abdicated the throne to Empress Gensho, Emperor Tenchi ordered the investiture based upon "the lay which is also irreversible like the universe and deemed as the permanent code." What was invested here includes the faculty of the Imperial Sun Succession (Amatsuhitsugi) to the Imperial Throne (Takamikura), and the governance of the nation (Osukuni amenoshita no matsurikoto). Although Genmyo is Shomu's grandmother and Gensho is his aunt, both of them call Shomu 'my son' in the imperial edict.

Imperial edict upon enthronement of Empress Koken (abdication edict of Emperor Shomu)

When Emperor Shomu abdicated the throne, he touched on the circumstances at the time of his enthronement, and referred to Fukai-no-Joten/ Fukaijoten. His words at that time are cited in the imperial edict of the enthronement of Empress Koken and as such they are archived. In the edict, Empress Gensho says that Emperor Tenchi ordered her to take the faculty of Imperial Sun Succession (Amatsuhitsugi) to the Imperial Throne (Takamikura) 'based on the spirit of the code firstly conceived and established,' and Empress Gensho ordered Seimu to succeed.
She says that although she herself took the Imperial Throne, the work is harsh on her health, and decided to abdicate the Imperial Throne to his son 'based on the spirit of the lay.'

There two theories of interpretation about the phrase 'based on the spirit of the lay' mentioned in the latter part without any adjectives; one advocates that this should be interpreted as Fukai-no-Joten/ Fukaijoten according to the context, and the other argues that this phrase is commonly used in other documents as well and it does not mean a certain specific law.

Imperial edict upon the enthronement of Emperor Kanmu

Since then, Fukai-no-Joten/ Fukaijoten had not been mentioned for a while, but it appeared again in the imperial edict upon the enthronement of Emperor Kanmu. Its outline is as follows: 'the emperor (Emperor Konin in concrete) ordered me to take the faculty of Imperial Sun Succession (Amatsuhitsugi) to the Imperial Throne (Takamikura) according to the law that Emperor Tenchi conceived and established for the first time.
I myself was afraid and dared not to proceed nor retreat, however since it is a order of the emperor, I take the Throne,'

Since this edict, the expression 'the law first conceived and established' by Emperor Tenchi started to be used, while the word 'Fukai-no-Joten/ Fukaijoten' had disappeared. Then, some theories argue that 'the law conceived and established for the first time' is a code modified from the original Fukai-no-Joten/ Fukaijoten, while others insist that it is a completely different one.

The form of Emperor Kanmu's edict was employed in the later successive emperors in the identical context and with almost the same wording. In 'Junna-Tenno Gosokui-ki ' (The record of the enthronement of Emperor Junna), the imperial edict upon enthronement of Emperor Junna is included. In 'Shoku-Nihongi' (Chronicles of Japan II), the imperial edict upon enthronement of Emperor Ninmyo. In "Nihon Sandai Jitsuroku" (sixth of the six classical Japanese history texts), the imperial edicts upon enthronement of Emperor Seiwa, Emperor Yozei, and Emperor Koko are included. All of the following edicts mention about 'the law that Emperor Tenchi established for the first time' in almost the same form: 'Gosanjo-in Gosokui-ki' which contains the imperial edicts upon enthronement of Emperor Gosanjo, 'Antoku-tenno Gosokui-ki' which contains that of Emperor Antoku, 'Shijo-in Gosokui-ki' which contains that of Emperor Shijo, 'Shugai-ki' which contains that of Emperor Gokashiwabara, and 'Goshodan-ki' which contains that of Nakamikado.

Since after the Heian period, it is noteworthy that a boilerplate collection called "Choya Gunsai" (Collected Official and Unofficial Writings) carries the examples of sentences for writing an imperial edict upon enthronement. A certain conformity found in the writing pattern of the edicts might be due to the fact that the edicts were written following such model phrases.

Imperial edict of the enthronement of Emperor Koko

However, even during the Heian period and after, the edict of Emperor Koko, who did not abdicate the throne from the former emperor, shows a slight difference.
While in the edicts of other emperors, there is a phrase that means 'to take the faculty of Imperial Sun Succession (Amatsuhitsugi) to the Imperial Throne (Takamikura) according the law that Emperor Tenchi established for the first time,' in the edict of KoKo this phrase is substituted by another phrase that says 'the faculty of Imperial Sun Succession (Amatsuhitsugi) to the Imperial Throne (Takamikura) is 'the law that Emperor Tenchi established for the first time.'
In the latter part, the phrases are identical with other edicts saying as follows; although Hyakuhekikei-shi (numerous close confidents) requested me, but I was afraid and dared not to proceed nor retreat, but finally I myself decided to take the throne.

Direct line imperial succession code theory and Legitimate child imperial succession code theory

The direct line imperial succession code theory, presented by Koyata IWAHASHI advocates that it is a law that limits the succession of the Imperial Throne to the direct line male children. According this theory, Fukai-no-Joten/ Fukaijoten was elaborated in order to reject the succession of the throne from the elder brother to his little brother, which was a form of succession frequently practiced until around that time. The first part in question in the Empress Gensho's edict upon enthronement, and the Emperor Shomu's edict upon enthronement as well as his edict upon abdication, referred to Fukai-no-Joten/ Fukaijoten as the base of authority that justifies the Emperor Shomu's succession of the Imperial Throne.

Shomu was still a young child when his father Emperor Monmu died, and did not fill the age requisite to take the throne. At this time, the way of imperial succession was to change from the form of elder brother to little brother succession to the form of father to son succession, and when the practice of succession between the direct line male children, from Tenmu to Kusakabe, Monmu, and Shomu, had faced with difficulties due to a series of young successors' deaths, it was sustained by the substitutional empresses, Jito, Genmei, and Gensho. The edict of Emperor Shomu as well as that of Empress Genmei can be easily understood, if you suppose that Fukai-no-Joten/ Fukaijoten was brought forward in order to cope with the old practice of the brother to brother succession.

The legitimate child (imperial) succession theory views the code as the law that further strengthen the limitation in the succession to the children of the legal wife, excluding the succession to any of the children born out of wedlock. Imperial Legitimate Child Succession Code Theory stands on the basis that since after Monmu, the Imperial Throne had been succeeded by imperial legitimate children, and that Ritsuryo (the legal codes of the Nara and Heian Periods) support the legitimate child succession principle.

The theory mentions three reasons why Emperor Tenchi instituted the code; intent of preventing the conflict in Imperial Throne succession, influence by China, and Prince Otomo's wish to succeed the throne. Until the generation of Emperor Tenchi himself, the succession had been commonly practiced between brothers, and naturally there are many eligible candidates, therefore the succession had been often settled by killing the rivals. Then, it is supposed that Emperor Tenchi, who were anxious to introduce the Chinese culture, might have conceptualized to introduce the practice of direct line succession in order to avoid bloodshed. There is a theory that advocates that the 'Emperor's Edict,' which Prince Otomo and his five senior vassals made an oath to guard by any means in 671, is Fukai-no-Joten/ Fukaijoten. Although "Nihonshoki" (Chronicles of Japan) does not touch on the contents of this 'Emperor's Edict,' judging from the context, it had been supposed to be the imperial decree to order Prince Otomo's succession of the throne.

There is a theory arguing that although the code advocates direct line succession, it was not created with the purpose of denying the principle of brother to brother succession, but permitting the princes whose mother was not from the imperial family to take the throne. At that time, in the Emperor's family. consanguineous marriage was commonly practiced and to be the heir to the Imperial Throne, his/her mother also was requested to be an imperial princess. Therefore, it is said that for the sake of Prince Otomo, whose mother is Iga no Ume, Emperor Tenchi made a law that dictates the direct line as the prerequisite of succession, and Empress Genmei took it up as Fukai-no-Joten/ Fukaijoten for the sake of Emperor Shomu, whose mother was from the Fujiwara clan.

However, according to this theory, it can be said that Fukai-no-Joten/ Fukaijoten was broken too soon, when Tenchi 's younger brother Emperor Tenmu presented himself to the next heir to the Imperial Throne. Even after that, the direct line and the legitimate child principles had not been strictly followed. About these points, the proponents of the direct line imperial succession (code) theory or the legitimate child imperial succession (code) theory explains that it is quite usual that the ideal presented in a law collides with other ideals or interests and has to face difficulties to fulfill.

Criticism against the direct line imperial succession code theory and the legitimate child imperial succession code theory

The direct line imperial succession code theory and the legitimate child imperial succession code theory are useful to explain the imperial edicts in the Nara period, however these theories had faced with many criticisms.

The first criticism is against the legitimate child imperial succession code theory, which says that Emperor Tenchi who had no legitimate child had no motive to institute the legitimate child imperial succession code. Emperor Tenchi had Prince Otomo (Emperor Kobun) with IGA no Uneme, but he had no child with Empress Yamatohime no Okimi.

The second criticism is related to the fact that the direct line emperors during the Nara period up to Emperor Shomu are not of the direct line of Emperor Tenchi but they belong to the line of Emperor Tenmu. If Fukai-no-Joten/ Fukaijoten is a direct line imperial succession code, Emperor Tenmu broke Fukai-no-Joten/ Fukaijoten to take the Imperial Throne, and therefore, it is unnatural that his descendents rely their legitimacy on Fukai-no-Joten/ Fukaijoten. This is especially detrimental for the argument base on the direct line imperial succession code, and for the argument based on the legitimate child succession code, Prince Otomo's authenticity as a heir can be deemed imperfect.

The third criticism is against the fact that in the imperial edict of Emperor Monmu, Fukai-no-Joten/Fukaijoten is not cited at the section to justify his enthronement. "Kaifuso" (Fond Recollections of Poetry) published in the Nara period reported that there were some objections within the imperial family, when Prince Karu was invested in the Crown Prince at a young age. At this time, Tenchi 's grandson, Kado no Okimi, insisted the direct line succession, however it seems that Monmu did not touch on the law which was established by Emperor Tenchi in his counter-argument. Also there is no reference to Fukai-no-Joten/ Fukaijoten in the imperial edict upon enthronement of Emperor Monmu. If Fukai-no-Joten/ Fukaijoten had instituted the direct line imperial succession, he would have alleged the legitimacy for his investiture of the Crown was based on it.

The fourth is related to the point that in the Emperor Genmei's imperial edict upon enthronement, Fukai-no-Joten/ Fukaijoten appeared for the second time is clearly described as the law of the nation's governance. There, the phrase 'the law of the nation's governance legislated as Fukai-no-Joten/ Fukaijoten' is found. Otsukuni' means to reside in the nation, and means governing the nation. Therefore, Fukai-no-Joten/ Fukaijoten is not a law related to the succession to the Imperial Throne, but it must be a law related to the governance.

The fifth criticism points out that in Emperor Koko's edict upon enthronement there is a descriptions that says 'the faculty of Imperial Sun Succession (Amatsuhitsugi) to the Imperial Throne (Takamikura) is 'the law established for the first time' by Emperor Tenchi. Amatsuhitsugi Takamikura (Imperial Sun Succession to the Imperial Throne)' indicates the position that the emperor assumes, and his faculty is the Imperial Throne itself or the administration that the emperor undertakes assuming the Imperial Throne, and it is not supposed to be the rule of succession.

Posterior pretext theory

The posterior pretext theory argues that Fukai-no-Joten/ Fukaijoten is not the code created by Emperor Tenchi, but after ages another person made it and lied that it was instituted by Tenchi. This theory is advocated to cover up the above mentioned first and third imperfections of the direct line succession code theory. This theory argues that the reason why the due description does not appear in the Emperor Monmu's imperial edict upon enthronement is because Fukai-no-Joten/ Fukaijoten did not exist at that time, and when the enthronement of Empress Genmei was to be celebrated or just before it, the code was created in order to justify the direct line (or the legitimate child) succession.

Against the pretext theory, some historians criticize that this theory should not give a detrimental rational forte to the direct line succession theories and the legitimate child succession theories, both of which are developed largely based on successive suppositions, to negate the explicitly written historical materials. There is also a question whether such a completely unfounded supposition can be used as a premise to persuade the people. Especially when Empress Genmei took the Throne, there were still some persons alive including ISONOKAMI no Maro who knew the reign of Emperor Tenchi.

The pretext theory is sometimes associated with other theories than the direct line imperial succession code theory and the legitimate child imperial succession code theory.

The code of imperial succession by abdication theory

This is the theory arguing that Fukai-no-Joten/ Fukaijoten is a code to rule imperial succession, however, it does not decide who should take the Throne but establishes the practice in which the former emperor appoints and chooses his successor. Fukai-no-Joten/ Fukaijoten is elaborated with the purpose of denying the conventional form of succession practiced until the former dynasty through consultations and recommendations by a group of vassals, and establishing the right to the appointment of the successor within the emperor's authority, and consequently it tried to cut out the struggles related to imperial succession.

Against this theory, there is criticism pointing out that if it were a succession law, it can be used to justify such unusual cases as the successions of Empress Genmei, Empress Gensho, Emperor Junnin, and Emperor Konin, however the theory is not applied in these cases.

The crown prince system theory

The theory that Fukai-no-Joten/ Fukaijoten was formulated to establish the Crown Prince system was presented by Tei MORITA in 1993. There are many speculative theories on how the Crown Prince system was established in Japan (including the MORITA's theory). MORITA's theory advocates that the investiture of Crown Prince Otomo falls on the 10th year of the enthronement of Emperor Tenchi, and according to this theory, Fukai-no-Joten/ Fukaijoten compiles plural contents, and a part of them touches on the succession of Imperial Throne with the specific description that institutes the Crown Prince system. The theory also points out a part that declares the emperor's independent administration without counting on any deputies, and his argument on this point is consistent with that of the Sui-Tang style imperial autocrat theory that MIZUNO advocates.

The Taika Reforms theory

In the Edo period, Norinaga MOTOORI interpreted that Fukai-no-Joten/ Fukaijoten means a series of laws formulated during the Taika Reforms. Fukai-no-Joten/ Fukaijoten is said to be established by Emperor Tenchi for the first time, however, in "Nihonshoki" (Chronicles of Japan), there are only descriptions on legal amendment and no description on a newly instituted law is found. During the reign of Emperor Kotoku, the national system changed drastically. MOTOORI thought that, the formulation of the code, nevertheless, was not attributed to the work of Kotoku but to the achievement of Tenchi, because at that time the central role of the system reform was played by Prince Naka no Oe. Toward this theory, some scholars criticized that it is not appropriate to admit the fact that the dominance of the crown prince over the emperor's authority was advocated in the official oath like the imperial edict, ignoring the presence of the emperor, and nowadays, this theory is not supported.

The Omi-Ryo (Omi Administrative Code) theory

In "Toshi Kaden" (Biographies of the Fujiwara clan) and "Konin Kyakushiki" (a compilation of rules, regulations, and precedents covering the 119 years since the issue of the Taiho code in 702), it was reported that Emperor Tenchi instituted Omi-Ryo as the first administrative code in Japan. Regarding Fukai-no-Joten/ Fukaijoten as Omi-Ryo instituted in the first year of the era of Tenchi had been a commonly accepted theory from the Taisho period to the early Showa period. The phrase of Empress Genmei's imperial edict to the enthronement that says 'the law of the nation's governance legislated as Fukai-no-Joten/ Fukaijoten' cited later by Takashi TAKAHASHI is considered as a historically proofed reference. Since there is no objection that the law of the nation's governance is a law formulated to rule the nation, this can be the law for the governance of the nation at that time, or that means, Omi-Ryo instituted as the administrative code for the first time.

The criticism toward the Omi-Ryo theory points out the contradiction of calling Omi-Ryo 'Fukai-no-Joten/ Fukaijoten' even after the Taiho Code had been enacted.
That is to say, it is contradictory to call the revised law 'The Irreversible Code.'
The Omi-Ryo nonexistent theory that has become influential in the latter part of the 20th century denies the theory that identifies Omi-Ryo with Fukai-no-Joten/ Fukaijoten. Because the institution of Omi-Ryo is a fabricated story during the Heian period, and it is impossible to be talked about in the Nara period.

Moreover, it is difficult to think that Omi-Ryo contained the provision on the imperial succession. Not in Taiho Code nor in Yoro Code, there are no provisions related to imperial succession, and in any codes of the Tang Period no such provision existed.
If such a provision were included in Omi-Ryo, a uniquely Japanese rule would have been excluded at the time when Taiho Code was established, but if so it is inconsistent with the phrase, 'the law which should not be modified.'

The Fujiwara clan's assisted government theory

In 1969, Encho TAMURA presented the theory that it is the code which established the assisted government system by the Fujiwara clan. According to this theory, Emperor Tenchi who gave an important position to Kamatari FUJIWARA, ordered him to perpetuate a joint administration system, that is, an assisted government system that permitted the Emperor's family to grip the Imperial Throne and the Fujiwara clan to assist it. As the code was not codified nor promulgated, Emperor Tenmu, who provoked the Jinshin war/ disturbance, was not obliged to follow Fukai-no-Joten/ Fukaijoten, but Empress Jito, a daughter of Emperor Tenji, and other descendents of the female line took the lead in persuading him and made him follow. It is said that when the death of Emperor Tenmu made it impossible to practice this form of succession, the existence of Fukai-no-Joten/ Fukaijoten, which had been kept a secret, was revealed to the public, in order to block the movements of the imperial family members that ware not able to count on the support of the Fujiwara clan. According to TAMURA, the prosperity of the Fujiwara clan at a later time had sprouted and prepared at that moment.

Those who criticize this theory insist that it is not understandable why the Emperor's family had to think that it needed to give facilitations to the Fujiwara clan to the degree that the Emperor's family entrusted its own succession to the hand of the Fujiwara clan. They also say that the theory overestimates the positions of Kamatari and FUJIWARA no Fuhito.

The Sui-Tang style imperial autocrat theory

The theory arguing that it is a code that advocates the essential manners to rule the nation, such as the emperor's sovereignty over the nation and his posture to practice good governance, or more concretely, it is a code that instituted the despotic ruling, following the emperors in the periods of Sui and Tang. The theory is proposed by Ryutaro MIZUNO in 1975.
MIZUNO looked at the point that the Emperor Kanmu's edict summarized 'to accept the Imperial Throne according to the law that Emperor Tenchi established for the first time, and to take the charge,' was modified in the Emperor Montoku's edict and it says 'to take charge of the Imperial Throne according to the law Emperor Tenchi established for the first time,' dropping the words 'to accept.'
Then he supposed that Fukai-no-Joten/ Fukaijoten during the reign of Emperor Montoku was not considered as the code to rule imperial succession and Emperor Kanmu also had a similar understanding. If Fukai-no-Joten/ Fukaijoten is not formulated to rule imperial succession, but to advocate the ideal position of the emperors, the edicts of the former emperors as well as the edicts of these emperors in the Heian period would make sense. MIZUNO supposed that in the 6th and 7th century, there was a ruling system in which the country was not reigned by only one Okimi (great king) but was ruled by a group of rulers including Okimi, based on the division of domains, and that Emperor Tenchi tried to change such a function of Okimi (emperor).

General principle of imperial reign theory

Takashi TANAKA assumed that it was not a law to lay down detailed regulations, but to set up the basic principle that Japan was a country that would be successively ruled by the emperors. If standing on this assumption, it seems natural that the code has been cited by each emperor/empress upon his/her enthronement.

Toward this, some people pose a question on the reason why the Emperor's family needed to set up anew the principle of dominance by the imperial line, having had enjoyed until then a long history of sovereignty. And they insist that it is understandable if this code had long existed since the country's foundation and the descriptions in "Nihonshoki" and "Kojiki" (A Record of Ancient Matters) historically back up the existence, however, it doesn't make any sense if the people had followed it only because it was instituted by Emperor Tenchi.

The second Fukai-no-Joten/ Fukaijoten in the Empress Genmei's edict.

The second citation on Fukai-no-Joten in the edict of Empress Genmei, 'the law of the nation's governance legislated as Fukai-no-Joten/ Fukaijoten' is an important point of criticism toward the imperial succession code theory.

Takashi TAKAHASHI, the first person who paid attention to this point, argued that the law of the nation's governance means a law of ruling and therefore, naturally it means nothing, but the Rituryo codes, and the Ritsuryo established by Emperor Tenchi is Omi-Ryo, thus Fukai-no-Joten/ Fukaijoten is the Omi-Ryo.

Many of the supporters of the imperial succession code theory explain that the description including this expression means 'work to maintain the law formulated as the irreversible code not declined, stable, and sustained,' and as a whole, the description is conscious of the succession. Their argument stands on the belief that even if the description, the law of the nation's governance, is used in one place, it is rather natural to understand that the rest of the part is referring to the imperial succession code. Tei MORITA, one of the supporters of the imperial succession code theory, argues that Fukai-no-Joten/ Fukaijoten includes plural contents and one of them is the law related to the imperial succession, and he also supposed that the code contains another law related to the Imperial Throne.

There is also a theory saying that different from the rest of the part, the second part does not refer to Fukai-no-Joten/ Fukaijoten. Takashi TANAKA presented the theory that the first description and the second one are referring to different laws. The second citation in the edict of Empress Genmei specifically refers to Taiho code, unlike the other parts. Ryutaro MIZUNO, who studied the edicts of other emperors, concluded that the edicts are pronounced in the context in which the emperors call on government officials to work following the administrative policies and laws and codes, and thought that these are nothing more than administrative guiding principles of the emperors.

The argument that the two parts in question refer to different things is supported based upon the following facts: first, the word Fukai-no-Joten/ Fukaijoten is not a name of a concrete law by its nature, but part of an adjective; secondly, the second part is not specified with the word, 'established by Emperor Tenchi.'

However, many scholars consider that it is unnatural to think that the two different laws are similarly modified by the excessively long adjective phrase that means 'established as the irreversible and eternal code, which should not be modified as long as the universe exists and as long as the sun and the moon shed light' could exist in the same edict.

Inconsistency between the imperial succession theories and the collateral line succession.

Supporters of the imperial succession theory usually argue that the interpretation of laws during the reign of Emperor Kanmu, or later, differs from the way of the time before Emperor Kanmu. Because if they consider it a direct succession code, there is an inconsistency between the real cases in which the imperial throne was succeeded to an indirect descendent.

Although none of the Emperors, Junna, Ninmyo, and Gosanjo, is a son of the former emperor, in the imperial edicts, they declare that the Imperial Throne was handed down according to the law that Emperor Tenchi established for the first time. Emperor Koko does not mention that he took the Throne according to the law that Emperor Tenchi established for the first time, but he also touches on this law. In any of these cases, no trace of pervasive arrangement that they took the Throne against the law can be detected in the context.

There are also cases in which the relationship with the former emperor is of the direct line, but the relationship with the imperial prince who was to succeed the Throne was of the collateral line. Imperial Prince Sawara, who succeeded the throne from Emperor Kanmu, and Imperial Prince Tsunesada, who succeeded the Throne from Emperor Ninmyo are such cases. If Fukai-no-Joten/ Fukaijoten is a direct line imperial succession code or a legitimate child imperial succession code, it conflicts with the facts because the code was broken only a few days before or after the enthronement. However, there is another interpretation in the treatment of the imperial prince, in which it is said that Emperor Junna and Emperor Ninmyo, who undertook the collateral line succession, put up the late emperor's son. This is the scheme employed to recover the direct line succession, by putting himself as a transit emperor.

Code of dead-letter and cassation

Many of the scholars who support the direct line imperial succession code theory or the legitimate child imperial succession code theory think that Fukai-no-Joten/ Fukaijoten had become a dead letter after the reign of Emperor Kanmu, and it had continued to be written according to precedent without understanding the contents. "Choya gunsai" (Collected Official and Unofficial Writings) compiled at the end of the Heian period shows a model phrase of this part with almost exactly equal letters to that really used in the imperial edicts to the enthronement, and this can be used as evidence that the model phrase had been handed down by copying the example.

Some scholars argue that the degradation or interruption of Fukai-no-Joten/ Fukaijoten in the course of its transcendence is unthinkable and it is rather probable that the code had been deliberately carried to cassation with a series of such events as Prince Motoi's death, Emperor Koken's enthronement, and Funado no Okimi's investiture as Crown Prince.
According to this argument, the phrase appeared in the Emperor Kanmu's edict 'the law established for the first time' refers to another one different from 'Fukai-no-Joten/ Fukaijoten.'

The Omi-Ryo pretext theory

Shohachi HAYAKAWA more clearly argues that the law 'established for the first time' refers to Omi-Ryo.
This argument has two pillars; one is that it is difficult to think that this phrase is referring to an imperial succession code, because Emperor Koko's edict can be read as 'the Imperial Throne is the law instituted by Tenchi.'
Another pillar is the Omi-Ryo nonexistence Hypothesis, which argues that a story that Emperor Tenchi instituted Omi-Ryo was created during this period. Then he concludes that 'the law established for the first time' refers to Omi-Ryo, which was created to inflate the achievement of Emperor Tenchi, and the successive Ritsuryo codes (codes to control the centralized governance) all together.

Toward this, there is a criticism arguing that the phrase 'the Imperial Throne is a law instituted by Tenchi' is nonsensical, and special meaning should not be given to this part, but a dead letter process of the code is seen. This criticism also points out that it is unnatural to mention past codes to justify the enthronement and not the Yoro code (code promulgated in the Yoro period).

Doctrinal history

In the Edo period, Norinaga MOTOORI, who presented a theory on Fukai-no-Joten/ Fukaijoten (The Irreversible Permanent Code), advocated in his books "Shokki Rekicho Shoshikai" and "Shokki Senmyo Monmoku," that it refers to a series of laws instituted during the Taika Reforms. As its reason, he points out the fact that in the era of Emperor Tenchi, when "Nihonshoki" (Chronicles of Japan) was written, there were law amendments but no institution of a new law. He thought the code was established by Tenchi in the imperial edicts, because a series of big institutional reforms was promoted by Emperor Tenchi, although these reforms were initiated during the reign of Emperor Kotoku as the Taika Reforms.

Later, when it was proved that Omi-Ryo was instituted in the first year of the reign of Emperor Tenchi as the first Ritsuryo code, Fukai-no-Joten/ Fukaijoten had come to be identified as Omi-Ryo. Concretely, in the Taisho period, Hiroyuki MIURA presented his theory in "Zoku Hoseishi no Kenkyu" (A Study of the History of Law: Part II), and argued that the law described in the various imperial edicts upon enthronement, was Omi-Ryo code. MIURA also incorporated Norinaga's theory with his own, advocating that the phrase also means the whole legal system starting from the Taika Reforms to the laws created in the reign of Emperor Tenchi. During the early Showa period, Masajiro TAKIGAWA followed this theory and supposed that it should be Omi-Ryo. The academic society at that time regarded that Omi-Ryo was the first and the most revolutionary code in Japan, while Taiho Code and Yoro Code were merely its revisions. Therefore, everybody thought that there could be little doubt that such an important code instituted by Tenchi and followed by the successive emperors was nothing but Omi-Ryo, and there were no precise discussions.

In 1951 after the war, Koyata IWAHASHI presented an article titled 'The eternal code established by his majesty Emperor Tenchi.'
This article originated the study on Fukai-no-Joten/ Fukaijoten. IWAHASHI, after examined the edict of Emperor Shomu, pointed out that it is used as a rational base of the succession of the Imperial Throne, and presented the imperial succession code theory. And based on this, he denied the Omi-Ryo theory, supposing that Omi-Ryo did not include the provisions on imperial succession. Takashi TAKAHASHI opposed to his theory based on the phrase 'the law of the nation's governance legislated as Fukai-no-Joten/ Fukaijoten,' however, many of the scholars agreed with the IWAHASHI's theory. Recession of the Omi-Ryo theory in the discussion about Fukai-no-Joten was due to the Omi-Ryo nonexistence theory, which was advocated almost at the same moment. If Omi-Ryo is a hypothetical creation in the Heian period, Fukai-no-Joten/ Fukaijoten, which was referred to in the Nara period, cannot be Omi-Ryo by any means. Even those who supported the Omi-Ryo existence theory began to regard Omi-Ryo as one phase of the long procedure to consolidate the Ritsuryo system, and the code became considered less important.

Since then until the end of the 1960's, the imperial succession code theory underwent various corrections and additions.
In 1955, Kojiro NAOKI advocated the pretext theory by Empress Genmei in his article 'Emperor Tenchi and the Imperial Succession theory.'
NAOKI, later discarded the pretext theory, but the idea of pretext was succeeded by the supporters of the direct line imperial succession code theory and the legitimate child imperial succession code theory, as well as, those who denied the theory. In 1959, Shigeo KITAYAMA presented the theory supposing that the phrase 'Emperor's Edict' embraced by Prince Otomo and his senior statesmen could be Fukai-no-Joten/ Fukaijoten. Mitsusada INOUE, in his articles, 'Kodai no jotei' (The empresses in the ancient history of Japan) presented in 1964 as well as 'Kodai no kotaishi' (The crown princes in the ancient history of Japan) prepared in the same year, stated a theory that it was not the practice of the direct line succession as advocated by IWAHASHI but the practice of the legitimate child succession might have been established.

It was Encho TAMURA who inverted the trends in which the Imperial Succession theory was going to be an accepted theory, and in his article 'A study of Fukai-no-Joten/ Fukaijoten' presented in 1969, he criticized the Imperial Succession theory across the board, and presented the theory that it was to establish the assisted government system by the Fujiwara clan. TAMURA advocated that an unwritten code that set up the assisted government by Fujiwara clan was Fukai-no-Joten/ Fukaijoten. This theory gained a considerable support in 1970's, however, the motives of the Emperor's family side and the time of emergence of the Fujiwara clan in the theory were not convincing, and therefore, it had lost its power. After that, new theories on Fukai-no-Joten/ Fukaijoten was presented one after another and held active discussions, however, none of them had a relevant success.

After the boom of the new theories, in the 1980's and later, the direct line imperial succession code theory and the legitimate child imperial succession code theory were again deemed dominant, but their credibility has not been confirmed yet.