In ancient times there was no such office as that of Censor. From the highest chamberlain of Court down to the humblest workman of the people, all were free alike to offer their advice to the Throne.
With the Han dynasty, the functions of Censor became vested in a single individual officer, whose duty it was to advise on all matters involving the welfare of the empire generally, His was a sacred trust; and for this post it was necessary to choose men of resolution and of liberal minds, who could gauge the relative importance of events and entirely subordinate their own interests to those of the commonwealth. Seekers after notoriety or wealth found no place in their ranks.
During the Sung dynasty the number of Censors was increased to six; and later on their names were duly engraved upon wooden boards. But I, fearing lest these should be obliterated by time, caused them to be carved upon stone; so that future generations might point to the record and say, “such a one was loyal. Such a one was a traitor. Such a one was upright. Such a one was corrupt.” Verily this should give good cause for fear!