Er Cheng waishu 二程外書

Er Cheng waishu 二程外書 "Outer book of the two Cheng brothers", also called Henan Chengshi waishu 河南程氏外書, is a collection of teachings of the Northern Song-period 北宋 (960-1126) Neo-Confucian philosophers Cheng Hao 程顥 (1032-1085) and Cheng Yi 程頤 (1033-1107) compiled by a group of disciples and arranged by the scholar Zhu Xi 朱熹 (1130-1200). The book was finished in 1178.

It is divided into 12 chapters containing a range of different writings noted down by Zhu Guangting 朱光庭 (1037-1094), Chen Yuan 陳淵, Li Can 李參 (1006-1079), Feng Zhongshu 馮忠恕, Luo Congyan 羅從顏, Wang Ping 王蘋 and Shi Zizhi 時紫芝. Some additional parts have been compiled by Hu Anguo 胡安國 and You Zuo 游酢. The Waishu is a kind of supplement to the Er Cheng yishu 二程遺書, with each chapter reflecting the structure of the Yishu and serving as a supplement to that particular chapter. The title "outer book" has been attributed because of its heterogenous character, and because it contains a lot of hearsay missing the facts of direct teaching.

There is a print from the Kangxi reign-period 康熙 (1662-1722) published by Master Lü's 呂氏 Baogao Studio 寶誥堂. During the Republican era, the Zhonghua shuju Press 中華書局 in Shanghai published a facsimile of a Song-period print. The Er Cheng waishu is included in the series Guoxue jiben congshu 國學基本叢書 and Sibu beiyao 四部備要 as part of the collection Er Cheng quanshu 二程全書 "Complete writings of the two Cheng brothers".