1. Sun Tzŭ said: Raising a host of a hundred thousand men and marching them great distances entails heavy loss on the people and a drain on the resources of the State. The daily expenditure will amount to a thousand ounces of silver. There will be commotion at home and abroad, and men will drop down exhausted on the highways. As many as seven hundred thousand families will be impeded in their labor. 2. Hostile armies may face each other for years, striving for the victory which is decided in a single day. This being so, to remain in ignorance of the enemy’s condition simply because one grudges the outlay of a hundred ounces of silver in honours and emoluments, is the height of inhumanity. 3. One who acts thus is no leader of men, no present help to his sovereign, no master of victory. 4. Thus, what enables the wise sovereign and the good general to strike and conquer, and achieve things beyond the reach of ordinary men, is _foreknowledge_. 5. Now this foreknowledge cannot be elicited from spirits; it cannot be obtained inductively from experience, nor by any deductive calculation. 6. Knowledge of the enemy’s dispositions can only be obtained from other men. 7. Hence the use of spies, of whom there are five classes: (1) Local spies; (2) inward spies; (3) converted spies; (4) doomed spies; (5) surviving spies. 8. When these five kinds of spy are all at work, none can discover the secret system. This is called “divine manipulation of the threads.” It is the sovereign’s most precious faculty. 9. Having _local spies_ means employing the services of the inhabitants of a district. 10. Having _inward spies_, making use of officials of the enemy. 11. Having _converted spies_, getting hold of the enemy’s spies and using them for our own purposes. 12. Having _doomed spies_, doing certain things openly for purposes of deception, and allowing our own spies to know of them and report them to the enemy. 13. _Surviving spies_, finally, are those who bring back news from the enemy’s camp. 14. Hence it is that with none in the whole army are more intimate relations to be maintained than with spies. None should be more liberally rewarded. In no other business should greater secrecy be preserved. 15. Spies cannot be usefully employed without a certain intuitive sagacity. 16. They cannot be properly managed without benevolence and straightforwardness. 17. Without subtle ingenuity of mind, one cannot make certain of the truth of their reports. 18. Be subtle! be subtle! and use your spies for every kind of business. 19. If a secret piece of news is divulged by a spy before the time is ripe, he must be put to death together with the man to whom the secret was told.