The nine-rank system, also known as the nine grade controller system, was a system used to categorize and evaluate officials, and potential entrants into officialdom, in Imperial China. Created in the state of Cao Wei during the Three Kingdoms, it was in use through the Jin Dynasty and the Northern and Southern Dynasties, until it was superseded by the Imperial Examination system during the Sui Dynasty.
Background and Cao Wei periodEdit
The Nine-rank system was created after the end of the Han in 220 CE at the proposal of Chen Qun, a court official from the state of Cao Wei. It was also called the "Nine-rank method for classifying officials" (Jiu pin guan ren fa; 九品官人法).
The system was, in effect, a reorganisation of the Han Dynasty practice of recommending noteworthy locals for political office. Since 134 BCE, during the reign of Emperor Wu of Han, the Han court relied mainly on nomination by local magnates and officials as a way of identifying talent, by nominating them under titles such as Xiaolian (孝廉, Filial and Incorrupt) or Maocai (茂才, of Outstanding Talent).
Chen Qun's reform was a way of systematising the selection of candidates for political appointments in two ways: by creating a common scale of nine ranks to evaluate a person, and by appointing Controllers (中正) in the court to grade officials on this scale. In practice, not only potential entrants but existing officials were also graded, creating two parallel systems: a "candidacy grade" 资品, and a "service grade" 官品. 
The system was ostensibly based on a few criteria: moral probity, administrative ability, as well as the contributions of the person or his family to the newly-created Cao Wei regime. In practice, descent also played an important role; the service grade of a candidate's father had a bearing on their candidacy grade. 
The Nine-Rank system was originally intended to centralise the power of nominating and selecting appointees to office into the imperial court at Luoyang, though conflict remained between the right of evaluation between centrally-appointed Controllers, and the governors of the regions. Nonetheless, the continued instability and turmoil of the Three Kingdoms period meant that the Nine-Rank system was not fully or solely implemented; mentions of the old nomination system as the basis for identifying talent remain prevalent in early Cao Wei writings. 
There are no poor people in the upper ranks and no powerful families in the lower ones.— Liu Yi (an official of Jin), Jinshu: 45: 1274
The Nine-Rank system would become more dominant in the later years of the Cao Wei regime under the regency of the Sima clan, and into the early years of the Jin regime, during which time it had changed in nature. Under Sima Yan, the power of Controllers was expanded to include not only evaluation, but also the nomination of talent; and with the conquest of Wu by Jin and the subsequent peace, the system also became more systematised and formalised.  
Through these changes, the Nine-rank system also became more closely aligned with the interests of the powerful official clans who had come to dominate imperial politics since the Cao Wei period. The expanded powers of the appointed Controllers in turn meant that the officials who held the post, many of whom came from these clans, could use their powers to promote the interests of their own scions. 
While the Nine-rank system helped powerful clans to dominate official posts in the court, it also helped stimulate private schooling within families as a means of transmitting knowledge that could increase one's standing as someone eligible for evaluation. An example of this intra-familial transmission of skills is the calligrapher Wang Xizhi, of the Wang clan of Langya that was prominent during the Eastern Jin, whose sons Wang Ningzhi, Wang Huizhi and Wang Xianzhi were all famed calligraphers in their own right. The emphasis placed by the nine-rank system on moral attributes such as filial piety also led to the growth of 'familial instructions' (家训), which aimed to transmit moral teachings to children, as a genre of writing in the Jin and subsequent dynasties. 
Northern and Southern DynastiesEdit
During the Sui and Tang dynasties, recommendations were eventually marginalized and phased out of the recruiting process, although sponsorship continued to play an important part in reaching officialdom until the Song. In the Song era, candidates were able to present themselves for exams independently, and bureaucratic staff recruited directly through the imperial examination system became the norm.
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