Chapter 13 · The Use of Spies

Sun Tzu said: Raising a host of a hundred thousand men and marching them great distances entails heavy loss on the people. Hostile armies may face each other for years, striving for the victory which is decided in a single day. To remain in ignorance of the enemy's condition because one grudges a hundred ounces of gold is the height of inhumanity. What enables the wise sovereign and good general to strike and conquer is foreknowledge. This foreknowledge cannot be elicited from spirits, nor obtained from experience or calculation. Knowledge of the enemy's dispositions can only be obtained from other men. Hence the use of spies: local spies, inward spies, converted spies, doomed spies, and surviving spies. When these five kinds are all at work, none can discover the secret system. This is called 'divine manipulation of the threads' — the sovereign's most precious faculty. Of old, the rise of the Yin dynasty was due to Yi Zhi who had served under the Xia. Likewise, the rise of Zhou was due to Lu Ya who had served under the Yin. Therefore only the enlightened sovereign and wise general who use the highest intelligence for purposes of spying achieve great results. Spies are a most important element in war — on them depends an army's ability to move.