用間

The figure of 700,000 households disrupted by an army of 100,000 reflects the enormous logistical burden of ancient warfare. Commentators estimate a ratio of roughly 7:1 between support population and field troops, accounting for conscript labour, supply transport, and lost agricultural production.

不仁之至也 ('the height of inhumanity'): Sunzi inverts the conventional moral framing. Spending money on espionage is not immoral — refusing to spend on intelligence, and thereby sacrificing armies through ignorance, is the truly inhumane act. This is a characteristic Sunzi move: redefining virtue in strategic terms.

不可取於鬼神，不可象於事，不可驗於度: Three methods of divination are rejected. 鬼神 refers to spiritual consultation and oracle practices; 象於事 means reasoning by analogy from past events; 驗於度 means verification through astronomical or mathematical calculations. Sunzi insists that only human intelligence — spies — can reveal the enemy's true condition.

The five categories form a complete intelligence system. 鄉間 (local spies) provide ground-level information from the civilian population; 內間 (inside spies) penetrate the enemy's bureaucracy; 反間 (double agents) corrupt the enemy's own intelligence network; 死間 (expendable spies) are unwitting carriers of disinformation; 生間 (living spies) are professional operatives who survive to report back.

神紀: Literally 'divine thread' or 'spirit's warp.' 紀 originally refers to the warp threads on a loom — the hidden structural threads that hold everything together. The metaphor suggests an invisible web of intelligence that binds the entire operation. Translated as 'divine web' to capture both the invisibility and the systematic nature.

死間 ('expendable spies'): The literal meaning is 'dead spies.' These agents are not necessarily killed, but they are sacrificed in the sense that they unknowingly carry planted disinformation. When the enemy discovers the deception, the agent is typically executed — hence 'dead.' The term is translated as 'expendable' to convey the operational logic.

The triad of requirements — 聖智 (sagely wisdom), 仁義 (benevolence and righteousness), and 微妙 (subtlety) — elevates espionage from a dirty trade to a discipline requiring the highest human qualities. This passage is the foundation of Sunzi's argument that intelligence work is the noblest function of command.

莫親於間: 親 means 'close' or 'intimate.' The spymaster must have a closer personal relationship with his agents than with anyone else in the army. This is both operational necessity (agents must trust their handler absolutely) and a statement about the centrality of intelligence to command.

The abrupt shift to the death penalty for leaks (間事未發而先聞者) may seem harsh after the lofty language about wisdom and benevolence. But the juxtaposition is deliberate: the 'benevolence' required to run spies is not softness — it is the ability to inspire loyalty while enforcing absolute secrecy.

守將、左右、謁者、門者、舍人: This is a precise inventory of an enemy command structure. 守將 is the garrison commander; 左右 are his personal attendants and advisors; 謁者 are officials who control access (reception officers); 門者 are gate guards; 舍人 are household retainers. Knowing their names enables targeted recruitment, bribery, or assassination.

The double agent (反間) is the keystone of Sunzi's intelligence architecture. Every other type of spy depends on information gained through turned enemy agents. Double agents reveal the enemy's intelligence priorities, their operational methods, and the identities of their other operatives — enabling the entire network to be built or compromised.

因而利之，導而舍之: Literally 'exploit them through benefit, guide them and house them.' The sequence describes the classic recruitment of a double agent: first bribe (利), then direct (導), then provide safe harbour (舍). The process converts an enemy asset through incentives rather than coercion.

反間不可不厚也: 厚 means 'generous' or 'substantial' — double agents must receive the richest rewards because they take the greatest risks and provide the most strategically valuable intelligence. The double negative (不可不) adds emphasis: this is non-negotiable.

伊摯 (Yi Zhi) is Yi Yin (伊尹), the legendary minister who helped Tang of Shang (商湯) overthrow the Xia dynasty (c. 1600 BC). According to tradition, Yi Yin first served at the Xia court, learned its weaknesses from within, then defected to Shang with critical intelligence. Sunzi frames him as history's greatest spy.

呂牙 (Lü Ya) is Lü Shang (呂尚), better known as Jiang Ziya (姜子牙) or the Grand Duke (太公望). He served as strategist to King Wen and King Wu of Zhou in their overthrow of the Shang dynasty (c. 1046 BC). The Liutao (六韜), a military treatise attributed to him, is another of the Seven Military Classics alongside the Sunzi.

Sunzi's historical examples are carefully chosen. Both Yi Yin and Lü Ya were men of the highest calibre — statesmen and strategists, not mere informants. The term 上智 ('superior intelligence') means not just clever spies but the most brilliant minds of the age, deployed in intelligence roles. The implication: espionage is too important for second-rate men.

The final line — 此兵之要，三軍之所恃而動也 ('This is the essence of warfare — that on which the entire army depends before it can move') — is the conclusion of the entire Sunzi Bingfa. That the text ends not with a chapter on tactics or formations but on intelligence operations is itself the ultimate statement of Sunzi's philosophy: knowledge precedes and determines all action.

Some editions read 伊摯 as a reference to Yi Yin's personal name (摯 = Zhi), while others treat 摯 as a descriptor meaning 'earnest' or 'devoted.' The mainstream commentarial tradition, following Cao Cao, takes it as a proper name.