What did the ancients say that "books are divided into nine categories"?

In ancient times, there were judgments on the level of calligraphy very early, and the judgment angles were also different. We only need to have a brief understanding of it, and we don’t need to take it too seriously. For example, in his article "Mo Sou" written by Wei Xu of the Tang Dynasty, calligraphers before the Tang Dynasty and contemporary calligraphers were divided into three grades: upper, middle and lower. Each grade was further divided into upper, middle and lower grades, called "nine grades". Below, we will list some of the calligraphers we are relatively familiar with today among the nine grades:

The upper grade: Zhou Shihuang's large seal script, Qin Lisi's small seal script, Cui Yuan of the Later Han Dynasty, Cao Cao of the Later Han Dynasty, and Du of the Later Han Dynasty. Bodu Zhangcao, Han Zhangzhicao, Wei Zhongxu Zhengshu, Wang Xizhi Zhengshu, Xingcao, Zhang Xu Xiaocao, Zhengshu.

Upper-middle grade: Jin Suojing's running script, Jin Wei's wife Zheng, Xing, Qi Wangseng Qianxing, Cao, Jin Wang Xianzhi's Xing, Cao

Upper and lower grade: Jin Xie Anxing, Cao, Song Yang Xin Cao, Li, Zen Master Chen Zhiyong Zheng, Cao.

Medium and top grade: Ouyang Xunzheng, Xing, Lu and Cambodia's Xing, Cao, Chu Suiliangzheng, Xing, Li, Cao, Yu Shinanzheng, Cao

Middle-middle grade: Wu Sunquan Xing, Cao, Jin Wang's army, Cao, Zhou Yuxin Xing, Cao

Middle and lower grade: Song Xie Ling's running, Li, He Zhizhang's running script.

The lower and upper grades: Jin and Lu Jixing and Cao, Liang Jianwen Emperor Xing and Li.

The lower middle grade: Jin Shantao Xing, Li, Qi Wu Emperor Xing, Cao, Fang Xuanling Xing, Cao, Xue Ji Xing, Cao.

The lower grade: Xu Jing of Shu, Xing Cao, Mrs. Wei of Northern Qi, Zheng, Xing.

Even so, there are still many people above who are relatively unfamiliar to us. However, it needs to be reminded that even "low-grade" people are still great people and should not be underestimated.