Terrain

Sun Tzu classifies the ground itself into six types, each with its own rule. Accessible ground can be freely traversed by both sides — occupy the high, sunny spots first and guard your supply lines, and you will fight to advantage. Entangling ground is easy to leave but hard to return to: sally out only if the enemy is unprepared, because a failed attack with no easy retreat is disaster. Temporizing ground favours neither side to move first — lure the enemy out with a feigned retreat and strike when he is half-emerged. At narrow passes, garrison them first and wait; if the enemy holds them, follow only if they are weakly held. On precipitous heights, hold the sunny summit first; if the enemy is already there, do not follow — entice him down. At a great distance from an evenly-matched enemy, it is hard to provoke battle and unprofitable to fight. "These six are the principles connected with Earth," he writes; the responsible general must study them.

He then turns from terrain to the commander, naming six ways an army is brought to ruin — and insisting that none of them is the fault of heaven. Flight, when a force is hurled against another ten times its size; insubordination, when the common soldiers are too strong and their officers too weak; collapse, when the officers are too strong and the soldiers too weak; ruin, when higher officers are angry and insubordinate and attack on their own account out of resentment; disorganisation, when the general is weak and without authority and his arrangements are unstable; and rout, when a general fails to estimate the enemy's strength and pits a small force against a large one. "These are six ways of courting defeat, which must be carefully noted by the general who has attained a responsible post."

Knowledge of terrain is therefore an active weapon: "The natural formation of the country is the soldier's best ally; but a power of estimating the adversary, of controlling the forces of victory, and of shrewdly calculating difficulties, dangers and distances, constitutes the test of a great general." He who knows these things and acts on them will win; he who does not will fail. So firmly does Sun Tzu trust this calculus that he licenses disobedience: if the situation promises certain victory, the general may fight even if the sovereign forbids it; if it promises defeat, he may refuse battle even if commanded to attack.

The ideal commander advances without coveting fame and retreats without fearing disgrace, his only thought to protect his country and do good service for his sovereign — "such a general is the jewel of the kingdom." On the treatment of troops he is precise: regard your soldiers as your children and they will follow you into the deepest valleys; look on them as your own beloved sons and they will stand by you even unto death. But indulgence without authority is useless — soldiers so pampered that they cannot be commanded are "like spoiled children; they are useless for any practical purpose."

The chapter closes with the completed formula of self-knowledge: "If you know the enemy and know yourself, your victory will not stand in doubt; if you know Heaven and know Earth, you may make your victory complete." The practical lesson is that most failures we blame on circumstance are really failures of reading circumstance — terrain is information, and misreading information is a competence problem, not bad luck.