The jiupin zhongzheng zhi 九品中正制 "system of the rectification of the nine ranks", also called jiupin guanren fa 九品官人法 "method of the classification of officials into nine ranks", was a method to rank offices (and the salaries of the office holders) according to the importance of the post, combined with a method of appointment in which candidates were likewise graded into nine ranks and allowed to fill vacancies of a matching rank.
The classification of state offices into nine ranks was already known during the Zhou period 周 (11th cent.-221 BCE), as jiuji 九級 or jiuming 九命. During the Han period 漢 (206 BCE-220 CE) the rank of officials was indicated by their annual salary, expressed in bushels of grain. There were 16 ranks during the Former Han 前漢 (206 BCE-8 CE), and 13 during the Later Han period 後漢 (25-220 CE), from "middle" 2,000 shi to 100 shi (see weights and measures).
The nine-rank system for the selection of officials was introduced by Cao Pi 曹丕 (Emperor Wen 魏文帝, r. 220-226), king of Wei 魏, shortly before he usurped the imperial throne and became emperor of the Wei dynasty. It had been proposed and drafted by Chen Qun 陳群, Minister of Personnel (libu shangshu 吏部尚書). With some changes, the system was perfected until the beginning of the Tang period 唐 (618-907).
In each commandery, a so-called rectifier (zhongzheng 中正) was appointed, and in each province a grand rectifier (da zhengzhong 大中正). Their posts were filled with with local persons recommended by the highest official of the commandery, later by that of the province. The rectifiers were subordinates to the Ministry of Education (situ 司徒). The rank of the rectifier himself was called xiangpin 鄉品 "township grade", and was normally the same as that of the vacant post. If it was higher the holder was called a "pure official" (qingguan 清官) or "official above the families" (qijiaguan 起家官). If it was lower, the term "impure official" (zhuoguan 濁官) was used.
Rectifiers had a staff of "visitors" (fangwen 訪問) at hand who carried out the selection of candidates for offices. The evaluation was based on criteria, namely the reputation of the family over several generations (jiashi 家世, mendi 門第), the personal character and moral conduct (daode 道德), and functional suitability (caineng 才能). The investigation of the family background based on family chronicles (bufa 簿閥, bushi 簿世), where merits and offices of all family members were recorded. While these matters were verifiable facts, the "soft criteria" were called zhuang 狀 "appearance" and depended on the assessment by others.
All recommendable persons were ranked into nine grades of "quality" (pin 品), namely shangshang 上上 (best), shangzhong 上中, shangxia 上下, zhongshang 中上, zhongzhong 中中, zhongxia 中下, xiashang 下上, xiazhong 下中, and xiaxia 下下 (lowest). Yet in practice, the grades shangpin 上品 "good" and xiapin 下品 "mediocre" were used. In reality, no one was given the first grade (yipin 一品), so the second one (erpin 二品) was in fact the highest achievable one. During the Wei period rank 3 (sanpin 三品) was still valued relatively high, but became a less favourable one (beipin 卑品, xiapin 下品) from the Western Jin period 西晉 (265-316) on. The decisions of the rectifiers were submitted to the Ministry of Eduction where they were counter-checked and handed over to the Ministry of Personnel (libu 吏部). Assessment were carried out once in three years.
The nine-rank system was an advancement of the selection procedure used during the Han period. The latter was mainly based on "moral" criteria and the reputation of the families, yet with strict rules for decision. In the turbulent decades of the early 3rd century such a detailed procedure was not possible. The warlord Cao Cao 曹操 therefore sought to apply more practical methods to have selected the most competent and trustful persons for his service. Yet he hid not fully abandon the recommendation of local dignitaries. When he conquered the province of Jingzhou 荊州 (central China), for instance, he trusted the recommendations of Han Song 韓嵩, and for more than ten years, Cui Yan 崔琰 and Mao Jie 毛玠 took over the selection of competent personnel for Cao Cao. In his eyes, competence was better than reputation or "moral" criteria, and he therefore ordered "appoint just the most able ones" (wei cai shi ju 唯才是舉). In this way he would also be able to overcome the interference of private matters into the appointment system, a force today known as the guanxi network. The rectifiers later introduced by his son Cao Pi were only responsible to the government, and had to ignore all private contacts.
The nine-rank system was adopted by the Jin and the Southern Dynasties 南朝 (420~589), yet the criterion of competence was more and more overshadowed by that of the family background. This tendency had been initiated by the custom to appoint only rank-2 officials as rectifiers, and the largest number of them came from the rich and influential families (so-called menfa 門閥), and favoured candidates with similar background. The result was that all occupants of higher offices hailed from the great families, while common persons (hanmen 寒門) were only appointed to low-ranking offices. The system thus perpetuated the status of the wealthy and powerful families, instead of recruiting the most competent persons into the state service. The Sixteen Barbarian States 十六國 (300~430) and the Northern Dynasties 北朝 (386-581) were less inspired by the system – probably because its original spirit was already vane -, apart from Shi Le 石勒 of the Later Zhao 後趙 (319-350), and the early phase of the Northern Wei period 北魏 (386-534). The system became obsolete with the social change of the 7th century and the downfall of the old families.
Emperor Wu 梁武帝 of the Liang dynasty 梁 (502-557) had all state offices divided into 18 ranks (ban 班). This decision from 508 was abolished soon. The Northern Wei dynasty introduced in 493 the system of 9 ranks (pin 品) with 18 half-ranks (ji 級), each full rank being divided into "principal" (zheng 正, in translations indicated by the letter A) and "lower" (cong 從, B: 正一品 1A, 從一品 1B, 正二品 2A, 從二品 2B, 正三品 3A, 從三品 3B,...). Each half-rank was again divided into three grades, so that the whole system had a fine gradation of 54 steps. In 499 it was decided that the three highest ranks (1-3) were not subdivided, and all others only in two half-ranks, without further distinction. This system was more or less common until the end of the imperial era. The Tang had made a slight difference in the half-ranks of civilian and military offices.
Below the rank 9B, there were sub-officials serving the government. These were in late imperial China known as bu ru liu 不入流 "not in the common [system]".