Jeong On was one of the Korean political leaders in the 17th century. He was born at An-eum town in Gyeong-sang Province and at the age of 31 joined the school of Jeong In-hong who was the top student of Jo Sig. Therefore he belonged to the Northern Party which generally consisted of the politicians who were either from the western region of Gyeong-sang Province or Jo Sig's students. Jeong's political activities were the consistent reification of the principle of Neo-confucianism in which he believed. For example, protection the princes in the political cricis, he suffered from the 10 years' exile. When Ching invaded Joseon, he insisted on resisting the invaders to the bitter end. After the king's surrender he went into lonely retirement and never returned to the capital. He emphasized the political initiative of government officials rather than the king's power. And he suggested a theory according to which political parties could cooperate in the government. This is why he remained unforgettable despite his party's collapse with the downfall of King Gwanghae. Jeong was a conservative. It means that he tried to maintain the established social order and Neo-confucian principles. For these ideological reasons, he opposed the land survey which was necessary for the renewal of the national administrative system but might have charged the land-owning class some additional burden. He also opposed the policy of promoting the descendants of secondary wives to pass the official examination or to obtain the goverment office. He thus wanted to keep the discriminative social order.

Ⅰ. 머리말 
 Ⅱ. 정치적 행적 
 Ⅲ. 이념적 기반 및 행동 준칙 
 Ⅳ. 맺음말

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