The son of heaven is a title in the ancient regime; The father of the king, the mother of heaven and the son of heaven. According to Mencius Shang, the son of heaven should be the title of the combination of Tianjue and Renjue, but unfortunately, many people in later generations got Tianjue and gave it up.
The son of heaven once referred to the king or emperor (born by destiny, so it is called the son of heaven). It is said that in the Spring and Autumn Period and the Warring States Period, the statement of the son of heaven began to appear, but it has not yet become an orthodox title. The titles of king and son of heaven were still used by vassal States, which became popular after the Han Dynasty.
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The theory of "the son of heaven" has evolved with the changes and development of the times.
Sima Qian wrote historical records in the Han Dynasty, saying that since Yao and Shun, the monarchs of Xia, Shang, Zhou and Qin dynasties were all descendants of the Yellow Emperor. Therefore, these monarchs are worthy of the name. It is reasonable that Son of God, in the sense of blood, accumulated virtue from generation to generation and became the son of heaven. However, Liu Bang, the founding emperor of the Han Dynasty, was born a commoner, and his father had no name, so he could not find his previous lineage.
So Sima Qian didn't understand that he could be the son of heaven. He guessed that he was probably a great saint sent by heaven. Otherwise, he will not gain political power and become the son of heaven in a few years. In order to find Liu Bang's immortal descent, the Confucians in the Han Dynasty experienced nearly 200 years' efforts. Finally, Jia Kui, a Confucian, found in Zuo Zhuan that one of Yao's descendants was Liu Lei, who was a courtier in Xia Dynasty.
Liu Bang is a descendant of Liu Lei. In this way, Liu Bang can be traced back to the Yellow Emperor through Yao, and is considered to be a god. After Liu Bang, Wang Mang and Cao Pi became emperors, and they should be traced back to Shun and then to the Yellow Emperor to prove the rationality of being emperors.
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