Social interaction refers to the interaction between people; Chidu is the old name for letters. This book is written by Mr. Tan Zhengbi, a modern Chinese popular literature researcher. He divides the commonly used letters in ancient China into four categories: communication, congratulations, recommendation, and introduction. Each category has one outgoing letter and one reply letter, paired together, with brief notes and vernacular translations, which are clear and concise, and can be regarded as a tool book for the format of daily letters in the old days.
