Changes of Position and Responsibilities of the Three Departments in Central Government from the Tang Dynasty to the Song Dynasty Based on the Changes of the Administrative System

In early Tang period,the highest authority of the state was composed by Sansheng,including Shangshusheng(the Department of State Affairs),Menxiasheng(the Chancellery) and Zhongshusheng(the Imperial Secretariat).From the year of 723 A.D.through the early Northern Song period,the highest authority of the state was the general office of the prime minister(Zhongshumenxia).Along with the changes of the administrative system from Tang to Song,the roles,positions,and responsibilities of Sansheng changed progressively.All those changes can be defined as incremental evolution of administrative systems.