Why did people in the Tang Dynasty call officials appointed by the emperor "oblique officials"?

Let's talk about what an inclined official is first. Xieguan, like its name, was an official who was blocked only by proper relationship, which happened in the Tang Dynasty. As we all know, in ancient times, it was necessary to go through layers of selection to obtain official positions, and the process was particularly strict. It must be approved by many people, and finally the emperor has to write a letter of appointment to take effect. The origin of oblique sealing officials is that Princess Anle of the Tang Dynasty openly bought and sold officials and wanted to form her own power.

In Tang Zhongzong, Princess Anle claimed to be the wife of the emperor, and she wanted to be the second marquis. So she began to cultivate her power in the imperial court, so she publicly bought and sold officials, but she needed the emperor's signature. It is said that Princess Anle first covered her own words for the emperor Zhongzong to sign, but the emperor never read the documents and signed them directly. Later, Princess Anle appointed officials directly in the name of the emperor.

Because of this improper appointment and personnel system, the letter of appointment is different from that of a normal official. I was embarrassed to seal this appointment with ink, so I sealed it obliquely with ink. I was embarrassed to pass through the main entrance of Zhongshu Province, but through the side door. Officials who go up in this way will be laughed at by their colleagues. People's letters of appointment are red, while yours is black. Of course, they are three points shorter than people, so they are called "oblique officials".

Oblique officials don't have to do anything in the court, but they still get high salaries. Later, more and more people started the business of buying and selling officials by stealth, and the number of new officials reached tens of thousands every year. Some official positions are not enough, so there are two or more positions. After a long time, the court was in chaos. Later, it was not until Emperor Xuanzong of the Tang Dynasty ascended the throne and abolished the system of oblique sealing officials that it was solved.