《汉书·传·杜周传》
《易》说： 正其本，万事通顺协调，凡论事或许有无法立即实行的，求之古代没有记载，考查今天则吉凶相同，上面意志摇动民心就惑乱，要是这样制度就实在难以行得通。
《易》曰： 正其本，万物理。 凡事论有疑未可立行者，求之往古则典刑无，考之来今则吉凶同，卒摇易之则民心惑，若是者诚难施也。
The Book of Changes said: correct the root, everything will go smoothly, any matter may not be immediately implemented, if there is no record in the ancient, if the investigation of today has the same omen, if the emperor's will wavers and the people's hearts are confused, if the system is implemented like this, it will be difficult to follow.