The four books, University, The Doctrine of the Mean, The Analects of Confucius and Mencius, are collectively called. Song people took out two books, The Book of Rites, The University and The Doctrine of the Mean, to match The Analects of Confucius and Mencius. By the time of the Southern Song Dynasty, Zhu had written "Notes on Four Books", and the names of the four books were thus determined. Since then, the "Four Books" have been the required books for orthodox education in feudal society in China, and also the primary standard books for selecting candidates in the imperial examination. The abbreviations of the Five Classics, Poetry, Calligraphy, Ceremony, Book of Changes, Spring and Autumn Period, were first named in the period of Emperor Wu of the Han Dynasty. It contains rich historical materials of ancient China, is a compulsory teaching material in feudal times, and is used by the ruling class as a theoretical basis for propagating patriarchal feudalism. The Six Classics refers to the Six Classics, that is, in addition to the Five Classics, plus Jing Yue. Others refer to the Six Classics as "Six Arts", and all the six arts in Han Yu's Shi Shuo have spread to Xi. So there are still six classics, but Jing Yue is omitted.