During the reign of Emperor Wu of the Western Han Dynasty, two officials notorious for their harsh application of the law rose to power: one named Zhang Tang, and the other named Du Zhou.
As a child, Zhang Tang was fascinated by criminal trials and devoured legal texts. Later, through Tian Fen, the Marquis of Wu'an, he became an imperial censor. When handling a case involving the royal family, he enforced the law so strictly that over three hundred people were executed for their connections. Emperor Wu of Han, impressed by his sharpness, ordered him to work with Minister Zhao Yu to draft new legal codes.
Later, when Zhang Tang was ordered to investigate the King of Huainan's rebellion case, he executed many people. Even the two ministers Yan Zhu and Wu Bei, whom Emperor Wu of Han wanted to spare, could not escape death.
While Zhang Tang was notorious as a harsh official in history for his severe enforcement of the law, his son Zhang Anshi was known for his loyalty, integrity, and cautious conduct. Serving with distinction under Emperors Wu, Zhao, and Xuan, Zhang Anshi rose to the rank of Grand Marshal, and his descendants continued to hold high positions in the imperial court well into the Eastern Han Dynasty.
Du Zhou, once a subordinate of the infamous harsh official Zhang Tang, followed in his footsteps as a notorious tyrant. Ordered to punish deserting border soldiers, he wrongfully executed many. Later promoted to Tingwei, the chief judicial officer, he mimicked Zhang Tang's methods, using brutal torture to extract confessions and condemning countless innocent people to death.
But unlike Zhang Tang, he did not use the law as his guide when handling cases; instead, he was skilled at trimming his sails to the wind and reading the emperor's mood: for anyone the emperor wished to punish, he would fabricate charges without restraint; for anyone the emperor wished to pardon, he would exhaust every means to secure their release. During his tenure as Commandant of Justice, over a hundred high-ranking officials were imprisoned on the emperor's orders, and he handled more than a thousand cases each year, leaving the jails overflowing with inmates.
Because he always followed the emperor's will in handling cases, Emperor Wu of Han appointed him as Imperial Secretary. Yet officials and commoners alike hated him to the bone, a hatred that lasted until his death.
However, Du Zhou's youngest son, Du Yannian, much like Zhang Tang's son Zhang Anshi, was known for his generosity and sincerity, earning an excellent reputation. He rose to the position of Imperial Secretary, widely praised by his contemporaries.
The Song Dynasty scholar Wang Mao commented in his work *Ye Ke Cong Shu* on these two historical figures, saying: "Zhang Tang and Du Zhou were both infamous harsh officials. Yet their descendants, by changing their ways like a lute's strings retuned or a carriage's path redirected, managed to obscure their fathers' transgressions. It seems the fathers' sins were lightened by their children's virtue—a historical phenomenon worth pondering deeply!"
Later, the idiom "change strings and tracks" came to be used as a metaphor for altering one's original direction, plan, method, or attitude.
Source: *Ye Ke Cong Shu*, Chapter "Zhang Du Jie You Hou"
Meaning of the Idiom: Later, the Chinese idiom "改弦易辙" came to describe altering one's original direction, plan, method, or attitude.