What are the characteristics of letters compared with other communication methods?

The combination of practicality, aesthetics and appreciation. From article style to literary style. The form is free, flexible and changeable, and the integrity of the format is not emphasized. Sincere emotion and distinct personality. In the pre-Qin period, letters were mainly practical and mainly played the role of resignation. Such as a letter to Yan, an exhortation letter written by Reese. Except for some letters in the Han dynasty, most of them mainly express personal thoughts and feelings, and the scope of use of letters has expanded and the content has increased. Letters from home were born, such as Zhuo Wenjun's A Book of Harmony. Confessions and letters of recommendation appeared. For example, in the Wei and Jin Dynasties, letters changed from "reason" to "emotion", and emotion was better than reason. Literati not only regard letters as practical tools, but also regard letters as an independent literary style, using a lot of allusions, which is neat and literary. Such as Tao Hongjing's "Thank You Letter" and Wu Jun's "Letter with Zhu".