Why is posthumous title, the emperor of China, called "Emperor" and "Zong"?

"Emperor" is posthumous title and "Zong" is the temple name, which is not the same thing.

If a direct descendant of an emperor is in power, the former emperor is regarded as "ancestor" and "ancestor", and the meaning of ancestor is arranged in the ancestral temple for the prince and grandson to sacrifice. Reflect the characteristics of "home is the world".

Some dynasties did not arrange ancestral temples for the dead emperors, and later generations called them posthumous title, such as Wendi and Wudi. Posthumous title belongs to a simple evaluation of the emperor's deeds before his death.

Before the Tang Dynasty, there were few temple names, so they were common in posthumous title. After the Tang Dynasty, all emperors with heirs had temple names, mostly called ancestors and clans.