XIII. Using Spies

Sun Tzu said: In general, when an army of a hundred thousand is raised and sent on a campaign a thousand li away, the expenses of the people and the outlays of the government come to a thousand pieces of gold a day. There is turmoil at home and abroad, men are worn out on the roads, and seven hundred thousand households cannot attend to their work.¹ The two sides hold each other off for several years to contend for victory on a single day. To begrudge ranks, salaries, and a hundred pieces of gold, and so not know the enemy’s situation, is the height of inhumanity. Such a man is no general of the people, no aide to his ruler, no master of victory.

So what enables the enlightened sovereign and the wise general to move and defeat others, and to achieve successes beyond those of the crowd, is foreknowledge. Foreknowledge cannot be had from ghosts and spirits, cannot be drawn by analogy from events, cannot be verified by measurement. It must be had from men, from those who know the enemy’s situation.

So there are five kinds of spies to use: local spies, inside spies, turned spies, doomed spies, and surviving spies. When the five kinds of spies are all at work and no one knows their ways, it is called the divine thread, the treasure of the sovereign. Local spies are people of the enemy’s own countryside whom we employ. Inside spies are the enemy’s officials whom we employ. Turned spies are the enemy’s spies whom we employ. Doomed spies are those for whom we stage false business outside, letting our own spies learn of it and pass it on to the enemy’s spies. Surviving spies are those who come back to report.

So in the affairs of the Three Armies, none are held closer than spies, no rewards are richer than those for spies, and no business is more secret than that of spies. Only a sage can use spies; only one who is humane and just can employ spies; only one who is subtle and fine can get the truth from spies. Subtle, so subtle! There is nothing for which spies are not used. If a spy’s business is heard of before it has been carried out, the spy and those he told shall both die.

In general, whether it is an army we want to strike, a city we want to attack, or a person we want to kill, we must first know the names of the general in command, his attendants, his ushers, his gatekeepers, and his retainers, and have our spies search them out.

Tempt with gain the enemy spies who come to spy on us, lead them in, and house them; so turned spies can be won and used. Through them we learn, and so local spies and inside spies can be won and employed. Through them we learn, and so doomed spies can stage false business and carry it to the enemy. Through them we learn, and so surviving spies can come back as planned. The ruler must know all about the five kinds of spies, and the knowledge must come from the turned spies; so turned spies must be treated with great generosity.

In ancient times, when Yin rose, Yi Zhi was in Xia; when Zhou rose, Lü Ya was in Yin.² So only the enlightened sovereign and the wise general who can make men of the highest intelligence their spies will surely achieve great things. This is the essence of war, that on which the Three Armies depend in every move.

Notes

1. 1. By an old system, eight households formed a unit; when one sent a man to war, the other seven supported it. An army of a hundred thousand thus kept seven hundred thousand households from their work.

2. 2. Yi Zhi, better known as Yi Yin, had served the Xia before he became minister to Tang, founder of the Yin (Shang) dynasty. Lü Ya, better known as Lü Shang or Jiang Taigong, had lived under the Yin before he helped King Wu found the Zhou.