These are the words of Master Sun:
Gathering a host of hundreds of thousands of men and marching them across great distances causes the people great misery and saps the state of resources. The daily upkeep will amount to a thousand pieces of gold each day. Unrest will soon occur, and people will succumb to exhaustion on the highways. Hundreds of thousands of families will have their daily lives upended. Opposing armies may face each other for years on end while they strive for a victory that will be decided in a single day. It is therefore inhumane for the commander of an army to willfully stay ignorant about the designs of the enemy because he is too miserly to spend a few hundred ounces of silver in bribes and bestow some number of titles as bribes. A commander who does not employ bribes to gain insights into the enemy's designs is neither a good leader of men nor an asset to his sovereign, and he will not be victorious on the battlefield.
The wise sovereign and the skillful commander obtain for themselves knowledge of the future. With foreknowledge victory and conquest can be ensured, and those in possession of foreknowledge may reach for accomplishments beyond the reach of ordinary men. Foreknowledge, however, cannot be obtained by consulting the spirits. Nor can it be derived from experience and speculation. Rather, knowledge of what the enemy is going to do can only be obtained from men who are familiar with the dispositions of the enemy.
Thus you must employ agents to gain foreknowledge. There exist five classes of agents:
By using all five classes of agents, it is possible to create a secret network of informants that cannot be breached by the enemy. This is what is called "the divine pulling of strings." It is the most valuable tool available to a sovereign.
Local agents are people who live in the territory of the enemy. Embedded agents are the bureaucrats and officials of the enemy. Double agents are enemy agents whom we use for our own purpose. Doomed agents are used to misinform the enemy [by feeding these agents false information and letting them be captured by the enemy]. Surviving agents are agents who bring back news from the enemy's camp.
Thus no one in the whole army is in a position of greater trust than a valuable agent. No one should therefore be rewarded more richly than the valuable agent. And no other relationship should be shrouded in greater secrecy.
The employment of agents requires shrewdness.
Agents cannot by managed without a certain amount of kindness and candor. Yet to gauge the veracity of an agent's report requires an astute mind. You must think! Use your agents under all circumstances.
If one of your agents divulges a secret before the time is ripe, you must kill him quickly, and the person to whom he divulged your secret must also be killed.
Whether your goal is to crush an enemy army, capture a city, or assassinate a single man, you must begin by assembling the names of the enemy commander, his adjutants, his staff officers, his bodyguards, and his door-sentries. Your agents will complete this task for you.
The agents of the enemy must be found, and then tempted with bribes and put up in comfortable quarters. In this manner the agents of the enemy may be made into double agents who can help us attain the information needed to secure local agents and embedded agents. It is also the information provided by the double agents that allows us to field doomed agents who will taint the designs of the enemy with false information. Lastly, it is also the information of the double agents that lets us use surviving agents.
The objective of all five classes of agents is to provide you with knowledge about the designs of the enemy [the doomed agent does this by allowing you to shape the designs of the enemy]. To this end, it is the double agent who informs the work of the other classes of agent. It is therefore of utmost importance that the double agent be rewarded generously.
The ascension of the Yin dynasty [Shang dynasty] was owed to I Chih, who had served under the Hsia [Xia dynasty - i.e. the previous dynasty]. In the same manner the Chou dynasty [Zhou dynasty] came into being due to the actions of Lu Ya, who had served under the Yin [Shang dynasty - i.e. the previous dynasty].
The secret work of agents is a pivotal element of war, as an army's ability to make favorable maneuvers depends on the information provided by its agents. The enlightened sovereign and the wise commander therefore use their smartest men as agents, and through the actions of their agents, they achieve great deeds.
[Here ends The Art of War]