Shu Zhang Zhangshi bifa shi'er yi 述張長史筆法十二意

Shu Zhang Zhangshi bifa shi'er yi 述張長史筆法十二意, also called Shu Zhang Zhangshi bifa 述張長史筆法, is an essay on calligraphy written during the Tang period 唐 (618-907) by Yan Zhenqing 顔真卿 (709-785).

The text critically evaluates the calligraphy of "Administrator" (zhangshi 長史) Zhang Xu 張旭 (685-759). It is based on an earlier essay by Emperor Wu 梁武帝 (r. 502-549) of the Liang dynasty 梁 (502-557), whose Guan Zhong Yao bifa shi'er yi 觀鍾繇筆法十二意 evaluates the calligraphy of Zhong Yao 鍾繇 (151-230).

Yan's text first describes the process of seeking instruction from Zhang Xu on brush techniques. It then details how Zhang imparted his knowledge through a question-and-answer format. Finally, it discusses the similarities and differences between ancient and contemporary calligraphy. Zhang Xu was especially renowned for his mastery of the "grass script" (caoshu 草書), earning the nickname "Zhang the Mad" (Zhang Dian 張顛) or "Sage of the Grass Script" (caosheng 草聖). During his time, Zhang Xu's grass script, Li Bai's 李白 (701-762) poetry, and Pei Min's 裴旻 sword dance were regarded as the "Three Wonders" (sanjue 三絶).

During the discussions with his disciple Yan Zhengqing, Zhang Xu explained the twelve principles of brush technique to him in a question-and-answer format, analysing the similarities and differences between ancient and contemporary calligraphy. He provided a detailed explanation and justification of Zhong Yao’s old twelve principles, examining each one systematically. Yan's essay is an excellent reference for the interpretation and application of calligraphy and has had a profound influence on the development of later calligraphy.

The text can be found in the series Shuofu 説郛 and Lidai shufa lunwen xuan 歷代書法論文選.