Dengxizi 鄧析子 "Master Deng Xi", also called Dengzi 鄧子, is a legalist treatise attributed to the Spring and Autumn-period 春秋 (770-5th cent. BCE) politician Deng Xi 鄧析 (c. 545-501 BCE). Deng Xi was a high state official in the state of Zheng 鄭. He was killed by the regent Sichuan 駟歂, but according to the book Liezi 列子, by Zichan 子產. Apart from being rated a legalist, Deng Xi is the oldest representative of the philosophical school of "dialecticians" (mingjia 名家).
Deng Xi is credited with the invention of written law (zhuxing 竹刑 "bamboo penal law"). Before, law texts were only promulgated as edicts of the sovereign. The text of the edict was then cast into bronze vessels, a custom introduced by chief counsellor Zichan (see the Zichan xingding 子產刑鼎). The transfer of the text to bamboo slips made it an easy-to-handle - even if easily decayable - book that could be copied whenever and wherever needed.
Deng Xi's conflict with Zichan developed around a method to remonstrance against the duke of Zheng. Deng Xi invented the open letter to the ruler (xianshu 縣書 "public letter") which was soon prohibited by Zichan. Deng Xi then resorted to the instrument of personal memorial (zhishu 致書 "effective letter"), which was also soon declared illegal by Zichan. Deng's final method of remonstrance was the personally submitted enveloped letter (yishu 倚書).
The book Dengxizi is divided into two chapters (Wuhou 無厚, Zhuanci 轉辭). It stresses the importance of laws and regulations for a well-functioning administration. Power (shi 勢) was "the chariot of the ruler", and force (wei 威) his tactics. With the help of those two, a ruler would be able to safeguard his position. The book Dengxizi also contains some Daoist thoughts.
The Dengxizi is included in the series Siku quanshu 四庫全書, Zishu baijia 子書百家 (Baizi quanshu 百子全書), and Ershierzi 二十二子. In 1990, the Shanghai Guji Press 上海古籍出版社 published it in a modern edition, together with the books Shenzi 慎子, Yinwenzi 尹文子, and Heguanzi 鹖冠子.