Chapter 13
Sun Tzu said: Whenever an army of one hundred thousand men marches a thousand kilometers, the daily expenditure for the people and the state amounts to a thousand pieces of gold. With the country in turmoil both within and without, seven hundred thousand households are wearyingly toiling on the roads, unable to engage in peaceful farming. To fight for years in order to secure victory in a single day, yet to be stingy with honors and gold, and unwilling to employ spies, thereby remaining ignorant of the enemy's true situation—this is the utmost lack of benevolence! Such a person is unworthy to be a commander in the army or an advisor to the ruler, nor can they be considered a master of victory. The reason why wise rulers and capable commanders can so often defeat their enemies and achieve greater success than ordinary people is that they first understand the enemy's situation. To understand the enemy's situation beforehand, one cannot rely on ghosts and gods, nor draw analogies from past events, nor verify it through calculations. It can only be learned from human beings—these are the ones who know the enemy's situation.
There are five types of spies: local spies, internal spies, turned spies, sacrificial spies, and returning spies. When all five types of spies are used together, no one can fathom their secrets; this can be called a wonderful and mysterious system, a treasure of the ruler. Local spies are those who are employed from the enemy's territory; internal spies are those who are employed from within the enemy's court; turned spies are those who are enemy spies who are induced to serve us; sacrificial spies are those who are deliberately misled to disseminate false information, which our spies understand and consciously pass on to enemy spies; returning spies are those who can personally return to report on enemy conditions.
Among the trusted ones in the army, none are closer than spies; among the rewards in the army, none are more generous than those for spies; among the confidential matters in the army, none are more secret than those involving spies. Only wise and sagacious people can employ spies; those without benevolent virtue are insufficient to command spies, and those without subtle and ingenious analytical judgment cannot obtain true intelligence. Subtle, indeed, subtle! There is no place where spies are not used. If a plan involving spies is known before it is executed, both the spy and those to whom he has revealed the plan must be put to death.
Whenever one intends to attack an enemy force, capture a city, or kill an important enemy official, one must first understand the names of the enemy's commanding general, his trusted assistants, his clerks who handle reports, his gatekeepers, and his retainers and advisors. Orders must be given to our spies to ascertain these details with certainty. It is essential to identify enemy spies who have been sent over and, once captured, to buy them off with large sums of money and induce them to serve us. In this way, turned spies can be used. With information obtained from turned spies, appropriate individuals can be found within the enemy camp, and local and internal spies can be employed. With information obtained from turned spies, sacrificial spies can disseminate false intelligence and let the enemy know about it. Because we have obtained information from turned spies and avoided danger, returning spies can report back as scheduled. The five types of spies must be mastered by the ruler, and the key to mastering them lies in turned spies. Therefore, the treatment of turned spies cannot be too generous.
In ancient times, when the Yin dynasty rose to power, Yi Zhi served as a spy in Xia; when the Zhou dynasty rose to power, Jiang Ziya gathered intelligence in Yin. Therefore, among wise rulers and capable commanders, those who can employ very intelligent people as spies are bound to achieve great feats. This is the essence of military affairs and the foundation for military action.
