Bisuilun 筆髓論

Bisuilun 筆髓論 "The marrow of the brush" is an essay on calligraphy attributed to Yu Shinan 虞世南 (558-638), one of the great for masters of art of the early Tang period唐 (618-907; Tangchu sijia 唐初四家), the others being Ouyang Xun 歐陽詢 (557-641), Chu Suiliang 褚遂良 (596-658), and Xue Ji 薛稷 (649-713). Yu Shinan, courtesy name Boshi 伯施, hailed from Yuyao 余姚 in the prefecture of Yuezhou 越州 (today in Zhejiang province) and first served the Sui dynasty 隋 (581-618) as an assistant in the Palace Library (bishulang 祕書郎). Under the Tang, he was promoted to the post of Director of the Palace Library (bishujian 祕書監), and was awarded the nobility title of District Viscount of Yongxing 永興縣子. He is therefore also known as Yu Yongxing 虞永興. From his teacher Zhiyong 智永 (late 6th cent.), Yu learned the styles of standard script (zhengshu 正書), running script (xingshu 行書) and grass script (caoshu 草書).

The chapter Bianying 辨應 uses metaphors of command in war to describe the realization of calligraphy, with the artist's mind as the ruler, the hand as his counsellor, the shaft of the brush as the commander, and the hairs as soldiers, who operate in unison to draft fortress and moat (the resulting character). Another chapter is dedicated to the function of the wrist, which has to remain light and unrestricted. Other parts of the text explain the particular characters of the regular script, the running script, and the grass script. The last part discusses the artist's mental preparation for his work which aims to create a result "without acting forcibly" (wu wei 無爲), and without being bound to strict rules.

While the book Xuanhe shupu 宣和書譜 praises the Bisui 筆髓 as a standard book on calligraphy, the descriptive catalogue Shuhua shulu jieti 書畫書錄解題 of Yu Shaosong 余紹宋 (1883-1949) rates the text as crude and disparate, and thus assumes that Yu Shinan was not the author.

The text is found in the book Shuyuan jinghua 書苑精華 and in the series Shuofu 說郛 and Lidai shufa lunwen xuan 歷代書法論文選.