(Tang Taizong) Li Weigong wendui (唐太宗)李衛公問對

The book Tang Taizong Li Weigong wendui 唐太宗李衛公問對 "Li Weigong answering the questions of Emperor Tang Taizong", short Li Weigong wendui 李衛公問對, is a military treatise composed as a question-and-answer dialogue between Emperor Tang Taizong 唐太宗 (r. 626-649) and Li Jing 李靖 (571-649), Duke of Wei. It belongs to the Seven Military Classics (Wujing qishu 武經七書). The date of composition is unknown. Authorship is traditionally attributed to the Song-period 宋 (960-1279) writer Ruan Yi 阮逸 (jinshi degree 1027), but this is far from certain. The Yuan-period 元 (1279-1368) scholar Ma Duanlin 馬端臨 (1254-1323) argued that the received version must have been edited during the reign of Emperor Shenzong 宋神宗 (r. 1067-1085).

The discussion between the ruler and his minister centres around several antagonistic terms by which military tactics can be explained, namely unorthodox/orthodox (qi zheng 奇正), appearance/truth (xu shi 虛實), subject/object (zhu ke 主客), and attack/defence (gong shou 攻守). The book provides many examples from practical warfare, like the deployment of troops and their lining up during battle, the military system and strategic thought. It is shown that the orthodox formation always has to be adapted to the strength and the activity of the enemy, as well as to the territory and geographical conditions.

A very good example in the book of how both types, the orthodox as well as the unorthodox tactics, were employed is the battle of Huoyi 霍邑 in 617 when general Li Yuan 李淵 (566-635), the eventual founder of the Tang dynasty 唐 (618-907), defeated Song Laosheng 宋老生 (d. 617), a general of the Sui dynasty 隋 (581-618). With the fixed lines, the orthodox tactics or the real tactics, the enemy can be deceived while the unorthodox or "void" units attack him. This is the so-called "demonstrating of a shape" (shi xing 示形) which only served to conceal the real attackers. Territory can be used in the right way to make oneself subject or master of the enemy and to press the enemy into the position of the object. Attack and defence, Li Jing says, are interconnected with each other. The attack is the favourable turn of defence, and defence is the strategic plan or base for the attack. During the attack, hitting the inimical troops' hearts and shattering their fighting spirit is always necessary. During defence, it is vital to build up the defence walls and to stabilise the lines of the formation to strengthen the martial temper of the troops. Li Jing describes the importance of the so-called "six-flower formation" (liuhuazhen 六花陣) for large armies and camps, which allows stronger units to protect the weaker ones.

The book has been studied for centuries and is still very valued, although it also contains some superstitious aspects like the dependence on cosmological forces like Yin and Yang 陰陽 and the belief in fortune-telling.