Leishu, a class of works combining to some extent the features of encyclopedias and concordances, plays a vital role in the rsearch of historical science and collation of ancient books. It originated from the Caowei period (220) or the period of the Three Kingdoms. Its compilation began to vecome gradually popular in the Tang Dynasty and reached its peak in the Song Dynasty, which even the Ming and Qing dynasties couldn't match at all. The Leishu boom in the Song Dynasty is due to three reasons: The first reason is closely related to the policy of the Song rulers, who attached great importance to wenzhi (civil administration). They were fond of learning vigorously, advocated culture and education, and encouraged the compilation of leishu. Military officer as he was, Song Taizu (the first emperor of the Song Dynasty) propagated culture in a large way. He was good at gaining historical experience and learning lessons from the past dynasties through reading histouical books. Carrying forward the good traditions, Song Taizong (the second emperor of the Song Dynasty) repeatedly issued edicts to command the historiographers to search historical books and organizde scholar-officers to compile books. Following Taizu and Taizong, the successors and the other imperial family members all loved to read books. But a large quantity of books available made it impossible and unnecessary for the Song emperors to read them all in their spare time, hence the necessity of compiling encyclopedic leishu.
The second reason is that the imperial civil examination system was perfected in the Song Dynasty, under which a series of reform was done and fair competition was advocated regardless of the family status, Thus, an increased number of ordinary scholars took part in the imperial examinations, which stimulated the demand and compilation of books for that sake. Leishu, which consists of examination underwent a fundamental change at the same time. Some subjects such as Mingjingke were cancelled. The major subject Jingshike was a must for candidates, whose enrollment was based on Jingyi, a type of writing on the interpretation of classic works of Confucius. As a wide selection of Confucianism was too much for them to read before taking the examinations, leishu was their best choice. Therefore, the compilation and publishing of various kinds of leishu became a profitable operation, which in turn pushed forward the compilation of leishu.
The third reason is that the perfected block printing technology and better binding in the Song Dynasty laid a sound foundation for the printing and publishing of lieshu.
The Ming and Qing dynasties witnessed the reformation of the imperial civil service examination, for which was prescribed the eight-past essay known for its rigidity of form and poverty of ideas. As the typer of essay became the standard of enrolling scholars, the range of knowledge needed for such examinations was narrowed gradually, and the demand for leishu declined rapidly.
