《汉书·传·张陈王周传》
相，上辅佐天子调理阴阳，顺应四季，下按万物的规律办事，外镇抚四夷诸侯，内使百姓亲附，让卿大夫各自能承当他的职责。 
宰相者，上佐天子理阴阳，顺四时，下遂万物之宜，外填抚四夷诸侯，内亲附百姓，使卿大夫各得任其职也。 
The prime minister, who assists the emperor in adjusting yin and yang, follows the changing seasons, conforms to all the rules of all things on earth, guards the four geographical directions and subjugates the lords of foreign countries. They ensure that all the citizens of the country are devoted to their country and that all the officials can carry out their duties.