Sunzi opens by declaring that the conduct of war is a matter of life and death for the state, requiring careful deliberation based on five constant factors: the moral law, heaven, earth, the commander, and method and discipline. He establishes the fundamental premise that all warfare is based on deception, where the skilled general appears weak when strong and inactive when employing forces. Victory is achieved by avoiding the enemy's strength and striking at unprepared points, rendering protracted campaigns unnecessary because prolonged warfare invariably exhausts state resources and drains the populace.
The text details methods of tactical disposition and the manipulation of energy, contrasting direct and indirect tactics which, like the primary musical notes or basic colors, combine into an inexhaustible series of maneuvers. A commander must be adaptable, modifying plans to match the terrain and the adversary's movements. Sunzi categorizes various types of ground—from accessible and entangling to desperate—and outlines the specific measures required for each, emphasizing that soldiers placed in desperate straits will fight with supreme tenacity.
Special attention is dedicated to the reading of natural signs on the march, such as rising dust indicating the approach of chariots or startled birds revealing an ambuscade. The author warns against five besetting sins of a general, including recklessness, a hasty temper, and over-solicitude for the men. Discipline must be maintained through a balance of humanity and stern authority, ensuring that orders are executed without hesitation.
Finally, the treatise emphasizes the absolute necessity of foreknowledge, which cannot be obtained from spirits or calculation, but requires the systematic use of five classes of spies: local, inward, converted, doomed, and surviving spies. Treating these informants with utmost liberality and secrecy enables the enlightened ruler to anticipate enemy actions and achieve victory before a battle is even fought.
