SUN ZI said: Generally, when an army of one hundred thousahd is raised and dispatched on a distant war, the expenses borne by the people together with the disbursements made by the treasury will amount to a thousand pieces of gold per day.  There will be continuous commotion both at home and abroad; people will be involved with convoys and  exhausted from performing transportation services,  and seven hundred thousand households will be unable to continue their farmwork.

    Hostile armies confront each other for years in order to struggle for victory in a decisive battle; yet if one who begrudges the expenditure of one hundred pieces of gold in honours and emoluments remains ignorar t of his enemy's situation, he is completely devoid of humanity.  Such a man is no leader of the troops; no capable assistant to his sovereign; no master of victory.

    Now, the reason that the enlightened sovereign and the wise general conquer the enemy whenever they move and their achievements surpass those of ordinary men is that they have foreknowledge. This  'foreknowledge' cannot be elicited from spirits, nor from gods, nor by analogy with past events, nor by any deductivc calculations. It must be obtained  from the men who know the enemy situation.

    Hence, the use of spies, of whom there are five sorts:  native spies, internal spies, converted spies, doomed spies, and surviving spies. When all these five sorts of spies are at work and none knows their method of operation, it would be divinely intricate and constitutes the greatest treasure of a sovereign.  Native spies are those we employ from the enemy's country people.  Internal spies are enemy officials whom we employ.  Converted spies are enemy spies whom we employ.  Doomed spies are those of our own spies who are deliberately given false information and told to report it to the enemy.  Surviving spies are those who return from me enemy camp to report information.

    Hence, of all those in the army close to the commander, none is more intimate than the spies; of all rewards, none more liberal than those given to spies; of all matters, none is more confidential than those relating to spying operations.  He who is not sage cannot use spies.  He who is not humane and generous  cannot use spies. And he who is not delicate and subtle cannot get the truth out of them.Delicate  indeed! Truely  delicate! There is no place where espionage is not possible. If plans relating to spying operations are prematurely divulged, the spy and all those to whom he spoke of them should be put to death.

    Generally, whether it be armies that you wish. to strike, cities that you wish to attack; and individuals that you wish to assassinate, it is necessary to find out the names of the garrison commander, the aides-de-camp, the ushers, gatekeepers, and bodyguards. You must instruct your spies to ascertain these matters in minute detail.  It is essential to seek out enemy spies who have come to conduct espionage .against you and bribe them to serve you.  Courteously exhort them and give your instructions, then release them back home.  Thus, converted spies are recruited and used.  It is through the information brought by the converted spies that native and internal spies can be recruited and employed.  It is owing to their information, again, that the doomed spies, armed with false information, can be sent to convey it to the enemy.  Lastly, it is by their information that the surviving spies can come back and give information as scheduled.  The sovereign must have full knowledge of the  activities  of the five sorts of  spies.  And to know these depends upon the converted spies.  Therefore, it is mandatory that they be treated with the utmost liberality.

    In ancient times, the rise of the Shang  Dynasty was due to Yi Zhi, who had served under the Xia.  Likewise, the rise of the Zhou Dynasty was due to Lu Ya, who had served under the Yin. Therefore, it is only the enlightened sovereign and the wise general who are able to use the most intelligent people as spies and achieve great results.  Spying  operations are essential in war; upon them the army relies to make its every move.