Both the "nickname" and the "temple number" were used after the emperor's death, and were added by posterity, and only the era name was in front of the emperor! Although I have not studied the ancient name, temple number, and year number in depth, I also know a little bit! So, correct it and answer again! The question says that most of the emperors from the Han Dynasty to the Sui Dynasty were "emperors", starting from the Tang Dynasty, why did the emperors call them "zong numbers"? Because in the feudal dynasty before the Tang Dynasty, the temple number was very strict, and not every emperor had a temple number! However, after the death of the ancient empress, every emperor had a nickname!
More importantly, the titles of the emperors from the Han Dynasty to the Sui Dynasty were very short, and the title of "谥号" was commonly used! For example, Emperor Wen of Han (temple number Han Taizong), Emperor Jing of Han (no temple number), Emperor Wu of Han (Emperor Shizong of Han), Emperor Zhao of Han (no temple number), among which "Wen, Jing, Wu, and Zhao" are all nicknames! If the emperors of the Han Dynasty called the temple number, it is inappropriate, because some emperors did not have a temple number after death! In addition, the era name was only available during the Han Wudi period, and the era name was not fixed, so it could only be called a nickname! Like Emperor Wen of Sui and Emperor Wen of Sui, "Wen he jiong" is also a title, these titles are added after the emperor's death, according to the size of the merits in front of him, and later generations!
After the Tang Dynasty, because the name of the emperor was too long and the number was not fixed, historians were inconvenient to use the name and era name, and when calling the emperor, they used the temple title, that is, the "sect number" said in the question. Because the han dynasty to the Sui dynasty has only one word, after the Tang Dynasty, the number of words varies from several words to dozens of characters, and the emperor frequently changes the era name, and it is inconvenient to call the name and year number! For example, Tang Taizong, although the era name only uses a "Zhenguan", but the nickname "Wenwu Dasheng Daguang Xiao Emperor" is too long, and the temple number is always only two words, and it is easier to call the temple number! Therefore, Taizong, Gaozong, Xuanzong, Zhongzong, etc. are all temple numbers! In the Qing Dynasty in the history of our country, the emperor called the era name, not the temple number and the nickname! Because the emperors of the Ming and Qing dynasties had only one era name, most emperors called the era name.
Mainly because the emperor's title after the Tang Dynasty is too long, if the emperor in China's history is not long, he should all adopt the title of the title! However, the emperors after the Tang Dynasty had too long a nickname, and there was no way but to use the temple number! In the Ming and Qing dynasties, the era name is very fixed, and an emperor adopts an era name in his lifetime, so the Ming and Qing dynasties generally call the year number! However, the Ming Dynasty can also be called temple numbers and era names, such as Ming Taizu (temple number) Zhu Yuanzhang can also be called Hongwu Emperor (era name Hongwu), Ming Chengzu (temple number) Zhu Di can also be called Yongle Emperor (era name Yongle)! In the Qing Dynasty, basically called the era name, such as the Kangxi Emperor, the Qianlong Emperor, if you say qing shengzu, qing gaozong estimated that there are few memories of recognition, once the emperor's era name is said, then generally remember who this emperor is!