Shufa yueyan 書法約言 "Conventional rules of calligraphy" is a brief book on the theory of art written during the early Qing period 清 (1644-1911) by Song Cao 宋曹 (1620-1701), courtesy name Binchen 彬臣 or Binchen 邠臣, style Sheling 射陵 or Genghai Qianfu 耕海潛夫, from Yancheng 鹽城, Jiangsu. In the late Ming period 明 (1368-1644), Song was a central-government secretary (zhongshu 中書), but ceased to serve under the new dynasty.
Song's book consists of an introduction, questions and answers to calligraphy based on Wei Shuo's 衛鑠 (272-349) Bizhentu 筆陣圖, and Sun Guoting's 孫過庭 (646-691) Shupu 書譜, basics for learning to write, and discussions of the writing styles standard script (kaishu 楷書), "running script" (xingshu 行書), and "grass script" (caoshu 草書). Much of the book derives from Song Cao's own thoughts. He believes that the brushwork of calligraphy should be light and elegant, rather than flamboyant; smooth, rather than tight; subtle, rather than explicit; and natural, rather than pretentious. The excellence (miao 妙) of calligraphy seen in "combination", and its spirit (shen 神) in "separation". Song stressed that a beginner should not spend too much time on paper and ink by copying model calligraphies, but should take good copies or rubbings of outstanding old calligraphies, emulate them carefully, thus become familiar with them, and then advance to go on to memorize exactly the shapes and movements of characters (bei tie 背帖) to imitate model characters. In order to become an expert, it was important to combine thought or plan with practice, constant repetition, and to have a good idea of what planned to create before putting the pen to paper.
The book is included in the series Zhaodai congshu 昭代叢書, Meishu congshu 美術叢書 and Lidai shufa lunwen xuan 歷代書法論文選.