1. In the first year of Zhenguan (627), Li Shimin ascended the throne and appointed Wei Zheng as Shangshu Zuocheng. Li Shimin was determined to establish a prosperous age, so he summoned Wei Zheng to his bed many times to inquire about the gains and losses. Wei Zheng spoke frankly and gave advice on more than 200 matters, which Li Shimin fully accepted.
2. In the same year, the former prince Li Jiancheng and the former relatives of Qi King Li Yuanji in Hebei were in danger due to the Xuanwumen Incident. Li Shimin sent Wei Zheng to Hebei to pacify them. On the way, Wei Zheng happened to meet Prince Qianniu Li Zhian and King Qi's guard Li Sixing being escorted to the capital. Wei Zheng asked them to be released and still appointed officials, so that the old relatives of the Prince of Hebei would believe that Li Shimin really wanted to pardon them.
3. In the third year of Zhenguan (629), Wei Zheng was appointed as Secretary Supervisor and began to participate in government affairs. Wei Zheng reported to Li Shimin that he led scholars to divide the ancient books into four parts and correct them.
4. In the fifth year of Zhenguan (631), Li Shimin talked with Wei Zheng about selecting an official. Wei Zheng said that he should first understand his talents, and then examine his moral character and hobbies. Princess Li Lizhi of Changle was born to Empress Changsun. Li Shimin was particularly fond of her and betrothed her to Changsun Chong, the son of Changsun Wuji.
5. In the sixth year of Zhenguan (the fifth year of Zhenguan in the old Tang book Wei Zheng), preparations for the dowry began. Li Shimin of the Tang Dynasty said to the ministers, "Princess Changle was born to the queen, and I and the queen love her. Now I will When surrendering, the etiquette should be increased." The ministers expressed one after another that "Your Majesty loves you and wants to do less", so they proposed to request double the number of princesses in Yongjia, and Li Shimin readily agreed.
However, Wei Zheng opposed this. Because Princess Yongjia is the aunt of Princess Changle. This move went beyond etiquette. Li Shimin returned to the palace and told Queen Changsun about the matter.
After learning about this, Empress Changsun lamented that Wei Zheng could "use etiquette and justice to suppress the feelings of the master" and praised him greatly. He specially sent people to reward Wei Zheng with 400 pieces of silk and 400 coins, and sent a message saying: "I heard that you are upright, and now I have seen it. I hope you will maintain it and not change."
When Li Shimin did not express anything, Empress Changsun directly rewarded Wei Zheng and hinted that she would provide support, which can be said to have given Wei Zheng a boost. It was precisely because of a backer like Empress Changsun that Wei Zheng's righteous admonishment went so smoothly. Soon Wei Zheng was promoted to the title of Duke.
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Wei Zheng (580-February 11, 643), courtesy name Xuancheng, was originally from Juluxiaquyang (now Jinzhou City). Politicians, thinkers, writers and historians of the Sui and Tang Dynasties were called "famous prime ministers of a generation" by later generations for their outspoken advice and assisting Emperor Taizong of the Tang Dynasty in establishing the "Government of Zhenguan".
In the seventeenth year of Zhenguan (643), Wei Zheng died of illness. He reached the rank of Guanglu Dafu and was granted the title of Duke of Zheng, with the posthumous title of "Wenzhen". The funeral was simple. In the same year, he entered Lingyan Pavilion.
He is the author of the preface to Sui Shu and the general introduction to Liang Shu, Chen Shu and Qi Shu. Most of his remarks can be found in "Zhenguan Zhengyi". Among them, the most famous one that has been handed down is the "Ten Thoughts on Admonishing Taizong".
Reference: Baidu Encyclopedia Wei Zheng