《孙子注解》Vol. 5

When circumstances are unfavorable, meeting the enemy head-on can bring heavy losses. In such a situation, one should instead encourage the troops, make use of stratagems to steady the situation, and watch for changes in the enemy. The text illustrates this principle with several battles: avoid the enemy’s first surge, hold firm to wear down their morale, and attack once they are exhausted.

At the outset, it says that if an attack offers no advantage, our own losses will be severe. The only sound course is to encourage the soldiers, devise more stratagems, and first observe how the enemy responds. Liu Bei’s side anticipated that Lu Xun would not take the bait, so it brought eight thousand troops out of the valleys where they had been lying in ambush. Lu Xun explained why he had forbidden the armies to pursue the forces under Ban: he suspected there was a trick behind their movements. The other generals said, “Liu Bei should have been attacked as soon as he first appeared. Now the armies have been facing each other across five, six, seven, or eight hundred li. The key positions are already firmly held, so another attack is unlikely to bring any advantage.” Lu Xun replied, “Liu Bei is a cunning enemy. When his forces first assembled, his attention was concentrated, and we could not attack him rashly. Now he has been stationed here for a long time without gaining an advantage. His troops are weary, his resolve is shaken, and he has no plan left. This is the moment to strike from both sides and defeat him.” Lu Xun first attacked one camp without success. He then said he had grasped how to defeat the enemy and ordered each soldier to carry bundles of reeds for a fire attack. They succeeded in taking the camp, and Liu Bei fled in defeat during the night.

Late in the Three Kingdoms period, the Wu general Zhuge Ke besieged Xincheng. Sima Jingwang (Sima Shi) sent Wuqiu Jian, Wen Qin, and others to resist him. When the two men asked to fight, Sima Jingwang said, “Ke has advanced deep into our territory with a lightly equipped force, as if he had sent his troops into a place of death. His initial assault will be hard to withstand. Xincheng is small but strongly fortified, and he may not be able to take it quickly.” He therefore ordered the armies to build high ramparts and hold their positions, wearing down the enemy. After several days of stalemate, Ke’s forces were exhausted by the siege and had lost more than half their men. Sima Jingwang then ordered Wen Qin to lead an elite force toward He Yu and cut off Ke’s route home. Afraid, Ke withdrew.

Liu Yao of Former Zhao sent a general to campaign against the Qiang. The Qiang leader Quan Qu held a fortified position in difficult terrain, and Liu Yao’s general You Ziyuan repeatedly defeated him. Quan Qu wanted to surrender, but his son Yi Yu boasted before everyone, “In the past, even when Liu Yao came in person, he could do nothing to me.” The next morning, Yi Yu advanced to the gates of You Ziyuan’s camp. You Ziyuan’s officers urged him to fight, but he said, “I have heard that Yi Yu has Zhuan Zhu’s courage and Qing Ji’s speed. His father has just been defeated, and his anger is at its height. The western tribes are fierce, and their first assault cannot be resisted. We should hold back and wait until their energy is spent before striking.” He therefore fortified his position and refused to fight. Yi Yu grew increasingly overconfident. Seizing the moment when the enemy was unprepared, You Ziyuan addressed his troops at midnight, had them feed their horses and eat before resting, then put on their armor and swept out of the camp at dawn. Later that morning, he laid an ambush and fought the enemy, capturing Yi Yu alive at the front of the formation.

During the Wude era of the Tang dynasty, Taizong led a campaign against Liu Wuzhou in Hedong. The Prince of Jiangxia, Li Daozong, was with the army. Taizong climbed Yubi to survey the enemy and asked, “The rebels rely on their numbers and have come to fight. What do you think?” Daozong replied, “The rebels are at the height of their momentum, and it will be hard to withstand them. We should overcome them by strategy rather than contesting strength. Have the troops dig deep ditches and build high ramparts to blunt their assault. A disorderly crowd cannot hold out for long. When their supplies run out, they will scatter on their own, and we can capture them without fighting.” Taizong said, “That accords with my own thinking.” Later, when the rebels ran out of provisions, they fled by night and were defeated in a single battle.

Taizong also campaigned against Xue Rengao at Zhedi. The rebels had more than a hundred thousand troops and repeatedly came out to challenge him. When the generals urged him to fight, Taizong said, “Our army has just suffered a setback, and its fighting spirit has not recovered. The rebels have won several sudden victories, so they will be overconfident and eager to fight. We should keep the gates closed and wear them down. Once their energy has ebbed, we can defeat them in one battle. This is the safest plan.” He ordered that anyone in the camp who spoke of fighting would be executed. As time passed, the rebels ran out of provisions, and their ranks became divided; officers and generals began surrendering one after another. Knowing that Rengao’s closest commanders were about to defect, Taizong said, “Now we can fight.” He ordered Commander-in-Chief Liang Shi to set up camp at Qianshui Plain to lure the enemy out. The rebel general Zong Luohou was arrogant and fierce. Unable to get the fight he wanted, he grew increasingly angry and threw his full strength into an assault on Liang Shi. Liang Shi held to the high ground and did not advance, blunting the enemy’s assault. Luohou pressed the attack even harder. Judging that the rebels were now exhausted, Taizong ordered his forces to engage at dawn. General Pang Yu took up position south of Qianshui Plain and first baited the enemy. Luohou brought his forces together for battle, and Pang Yu was nearly defeated. Taizong then personally led the main army out from the north of the plain, catching the enemy by surprise. Luohou turned his forces to resist. The Tang troops attacked from front and rear, their cries shaking the sky. Luohou’s courage failed, and his forces were routed.

Li Jing accompanied Li Xiaogong, Prince of Hejian, on a campaign against Xiao Xian. When they reached Yiling, Xiao Xian’s general Wen Shihong stationed tens of thousands of elite troops at Qingjiang. Xiaogong wanted to attack, but Li Jing said, “Shihong is one of Xiao Xian’s ablest generals. His soldiers are brave, and they have just come out through Jingmen with their whole force. They are an army coming to rescue a defeated side, and I fear we cannot withstand them. We should anchor on the south bank and avoid a direct clash. Once their energy has ebbed, a powerful attack will surely defeat them.” Xiaogong did not listen. He left Li Jing to guard the camp and went to fight in person. As predicted, he was defeated and fled to the south bank.

Zhang Yu explains the passage from the Art of War as follows: if the enemy advances on the strength of a victory, their momentum cannot be resisted; one should give way a little and wait for them to grow tired and lose heart. He also cites the standoff between Jin and Chu. At dawn, the Chu army advanced and formed its lines before the Jin forces. The Jin military historian was alarmed, but Yue Shu said, “The Chu army is reckless. Hold the ramparts and wait. In three days they will withdraw; if we attack as they retreat, we will surely win.” Zhang Yu then cites Taizong’s campaign against Xue Rengao: when the generals urged him to fight, Taizong kept the gates closed and wore the enemy down, then defeated it in a single battle once its energy had ebbed. The lesson in all these examples is the same: do not confront the enemy at the height of its strength. Hold your ground until it is exhausted, then strike once and win.

Do not take the bait—do not swallow the “lure” the enemy has deliberately set out.

On its face, Sunzi’s phrase means that you must not casually eat food the enemy has left behind, for fear that it may be poisoned. Li Quan cites cases in which Qin forces poisoned the water upstream and the Later Wei Prince of Jiyin, Xincheng, laid an ambush with poisoned wine. These examples show that when the enemy abandons food and drink, you must test it first rather than give in to appetite.

Commentators through the ages, however, have stressed that “bait” here does not mean only literal poison. Du Mu says it can also mean dangling a prize to draw you in. Chen Hao argues that in the battle between Cao Cao and Yuan Shao, when Xun You spoke of “baiting the enemy,” he may not have meant actual poison; more likely, the idea was to lure the enemy away from a favorable formation with the promise of gain. Mei Yaochen compares this to fishing: a fish that craves the bait dies, and an army that craves it is defeated. When the enemy tries to “fish” for you with military tactics, do not take the bait. Wang Xi adds that when someone tempts you with profit, a surprise ambush often lies behind it.

The commentaries also cite many historical examples: the people of Chu lured the state of Jiao into gathering firewood; the Red Eyebrows pretended to retreat and abandoned their baggage; Cao Cao abandoned baggage or released cattle and horses to lure Ma Chao; Yuan Shao’s army took abandoned baggage and was defeated; and Later Wei forces used a line of river defenses to tempt the enemy into raiding, then crushed them with an ambush. All follow the same pattern: deliberately leave an apparent prize in plain sight, wait for the enemy to reach for it, then strike for victory.

Zhang Yu quotes the Three Strategies: “Beneath fragrant bait, a fish is sure to hang.” An army that covets profit will be dealt with like a fish that bites the hook. So “baiting the enemy” does not refer only to poisoning food. Any use of goods, provisions, livestock, or a feigned retreat to hold the enemy in place or throw its formation into disorder counts as bait. Your response should be “do not take it”—do not covet a small, immediate gain.

Do not intercept or attack an army that is retreating home.

Li Quan explains: Soldiers who have set their minds on going home are difficult to restrain. Du Mu gives the example of Cao Cao’s campaign against Zhang Xiu: Cao Cao once used his baggage train as bait to lure Yuan Shao’s army. Li Ju likewise used cattle and horses as bait to lure Shi Le’s army.

Li Quan explains that soldiers who are bent on going home are difficult to restrain. Du Mu also recounts Cao Cao’s campaign against Zhang Xiu. Liu Biao sent troops to reinforce Zhang Xiu and tried to cut off Cao Cao’s retreat. As Cao Cao prepared to withdraw, Zhang Xiu’s forces pursued him, preventing Cao’s army from advancing. Liu Biao and Zhang Xiu then joined forces and held a strategic pass, trapping Cao Cao’s troops between enemies in front and behind. Cao Cao took advantage of the night to cut through the pass, make a tunnel, and move all the baggage through it. He then arranged an ambush. At daybreak, his infantry and cavalry attacked the enemy from both sides and routed Zhang Xiu. Cao Cao said to Xun Yu, “The enemy intercepted my retreating army and forced us into a position where we could only fight desperately. That is why I knew we would win.”

Meng Shi says: Soldiers who are thinking of going home will fight to the death once they are driven into a desperate position. It is therefore unwise to block their way and attack them. Du You says: Everyone has a family, a hometown, and a country to return to. Do not intercept them; instead, observe the situation for a while and then decide what to do. Mei Yaochen says: The enemy will certainly fight to the death. Wang Xi says: The soldiers will each fight with all their strength. Do not block their way home; if they still have other concerns, however, you may intercept and attack them.

When Cao Cao attacked Ye, Yuan Shang came to relieve the siege. His generals thought this was an army returning home and that it would be best to avoid it. Cao Cao said, “If Yuan Shang takes the main road, avoid him. If he comes by way of the western mountains, he will become our captive.” Taking the main road would show that he was intent on returning home; marching along the mountain paths would mean he still hoped to rely on the difficult terrain to fight and was afraid.

He Shi adds an account of Cao Cao’s campaign against Zhang Xiu. Zhang Xiu and Liu Biao joined forces and held a strategic pass, trapping Cao Cao’s army between enemies in front and behind. At night, Cao Cao dug a tunnel, moved his baggage through the pass, and set an ambush. At daybreak, the enemy thought Cao Cao was fleeing and pursued him with its whole force. Cao Cao then sent out his ambush, ordering the infantry and cavalry to attack from both sides, and routed the enemy. Cao Cao said to Xun Yu, “The enemy intercepted my retreating army and forced us into a position where we could only fight desperately. That is why I knew we would win.”

In the second year of the Jianwu era of Qi, Wei forces besieged Zhongli. Zhang Xintai served as an army commander and accompanied Cui Huijing to relieve the city. After the Wei forces withdrew, ten thousand soldiers remained on Shaoyang Islet. They asked for permission to pass through and offered five hundred horses in return. Cui Huijing wanted to block the road and attack them. Zhang Xintai advised him: “Do not intercept a retreating army; this is something the ancients feared. Soldiers in a desperate position must not be underestimated.” Cui Huijing therefore let them pass.

When Fu Jian of Former Qin campaigned against Eastern Jin, he reached Shouchun, was defeated, and withdrew. Murong Hong raised an army at Huaze, near Chang’an, and Fu Jian sent Fu Rui, Dou Chong, and Yao Chang to attack him. Fu Rui was brave and decisive, but he underestimated the enemy and showed little concern for his soldiers. When Murong Hong heard that Fu Rui was approaching with an army, he became afraid and prepared to lead his followers eastward, beyond the passes. Fu Rui sent troops to pursue and intercept them. Yao Chang advised him: “The Xianbei are intent on going home. You should drive them beyond the passes; do not intercept them.” Fu Rui ignored him. The two sides fought at Huaze, where Fu Rui was defeated and killed.

Lü Hong of Later Liang attacked Duan Ye at Zhangye but failed to prevail and prepared to withdraw eastward. Duan Ye discussed whether to send troops in pursuit. His general Juqu Mengxun advised him: “Do not intercept a retreating army or pursue an enemy trapped in a desperate position. These are rules of warfare. It would be better to let them go and deal with them later.” Duan Ye replied, “If we let the enemy go once, we will surely regret it.” He then led his troops in pursuit and was defeated by Lü Hong.

Zhang Yu says: When an army is fighting abroad, everyone is thinking of going home. If they are intercepted along the way, they will certainly fight to the death. Han Xin also said, “If we go along with the soldiers’ wish to return east, what could we not accomplish?” After Cao Cao defeated Liu Biao, he said to Xun Yu, “The enemy intercepted my retreating army, so I knew we would win.” When Lü Hong attacked Duan Ye, failed to prevail, and prepared to withdraw eastward, Duan Ye wanted to pursue him. Someone advised him, “Do not intercept a retreating army; this is a rule of warfare. It would be better to let them go and consider what to do later.” Duan Ye ignored the advice, led his troops in pursuit, and was ultimately defeated by Lü Hong. There are many other examples of this kind, too numerous to list one by one.

“Leave a Gap When Encircling an Army” (When surrounding enemy forces, always leave an opening.)

Cao Cao says: The Sima Fa teaches that when encircling the enemy, one should close off three sides and leave the fourth open, so the other side has a way to survive. Li Quan says: One must leave one side of the encirclement open to show that the enemy is not being hemmed in completely. If surrounded on all four sides, they will defend themselves to the death. Xiang Yu’s massacre of the people of Waihuang and Emperor Wu of Wei’s siege of Huguan both illustrate this principle. Du Mu says: Show the enemy a way out so they do not believe they must die, then take the opportunity to strike.

In the Later Han, the sorcerer Wei Si’s disciples Shan Chen, Fu Zhen, and others gathered in Yuanwu city, plundered officials, and called themselves generals. Emperor Guangwu sent Zang Gong with several thousand Northern Army troops to surround them. The rebels had ample provisions, and repeated assaults failed, causing casualties among the soldiers. The emperor summoned the ministers and princes to ask for advice. At the time, the future Emperor Ming was the Prince of Donghai. He replied: “These sorcerers are bound together by mutual dependence, and their position cannot last long. Some among them must already regret what they have done; it is only that the outer encirclement is too tight for them to escape. Ease it slightly and let people get out. A single village head would then be enough to capture them.” The emperor ordered the troops to open the encirclement and guard it less tightly. The rebels scattered, and Shan Chen, Fu Zhen, and the others were executed.

At the end of the Tianbao era in the Tang, Li Guangbi led the Shuofang army against Shi Siming at Tumen. The rebels retreated and were then surrounded on all sides. Li Guangbi ordered his troops to open the southeastern corner and let them through. Seeing the gap, the rebels threw down their armor and fled in haste; the pursuers wiped them out. This is what it means to open one side.

Du You says: When encircling an enemy on open, level ground, leave one side open to make the encirclement appear weak, so that the enemy’s resolve to fight or hold out is shaken and they consider whether to stay or flee. But if the enemy occupies dangerous terrain, faces imminent peril, and has outside forces coming to its aid, the encirclement should be made secure; there is no need to leave an opening. That is the proper way to use troops. Mei Yaochen agrees with Cao Cao’s interpretation.

He Shi gives these examples: Early in the Later Han, Zhang Bu controlled Qi, and Geng Yan campaigned against him. Zhang’s general Fei Yi defended Lixia and sent other forces to hold Zhue and Zhongcheng. Geng Yan first attacked Zhue and took it between dawn and noon. He then opened one corner of the encirclement, allowing its defenders to flee toward Zhongcheng. When the people of Zhongcheng heard that Zhue had fallen, they panicked and abandoned the city.

In another case, Zhu Jun and Xu Qiu pursued the remaining Yellow Turban rebels. Han Zhong held Wancheng and asked to surrender, but his request was refused. The attackers pressed their assault, yet could not take the city. Zhu Jun said to Zhang Chao: “The rebels are surrounded on all sides and pressed hard from within. They asked to surrender and were refused, and now they cannot get out. That is why they are fighting to the death. Even ten thousand people united in this way are hard to withstand—what of a hundred thousand? Nothing could be worse. We should withdraw the encirclement and move our forces inside the city. When Han Zhong sees the siege lifted, he will certainly come out. Once he does, his resolve will be scattered, and he will be easy to defeat.” They did as he advised. Han Zhong came out to fight and was defeated.

When Emperor Wu of Wei besieged Huguan, he ordered that everyone be buried alive if the city fell. The siege dragged on for months without success. Cao Ren said: “When besieging a city, one must show a way to live and open a path of escape. Now that you have declared everyone will die, they will defend themselves as individuals. The city is strong and has ample provisions. If we attack, our soldiers will be injured; if we hold the siege, it will take a long time. Keeping troops tied down beneath a strong city to attack people who expect certain death is no sound plan.” The emperor followed this advice, opened the way into the city, and the defenders surrendered.

Late in the Northern Wei, Gao Huan raised an uprising in Hebei. The four generals Erzhu Zhao, Erzhu Tianguang, Erzhu Dulü, and Erzhu Zhongyuan joined forces south of Ye, claiming to command two hundred thousand troops, and surrounded Gao Huan at Nanlingshan. Gao Huan had two thousand cavalry and fewer than thirty thousand infantry. The four generals failed to close the encirclement completely. Gao Huan linked oxen and donkeys together to block the road back, and his officers and soldiers fought desperately, striking out on all four sides. They inflicted a great defeat on Erzhu Zhao and the others.

Zhang Yu says: Surround the enemy on three sides and leave one corner open. Show them a way to live so they will not fight with unyielding resolve. Zhu Jun’s siege of Han Zhong at Wancheng in the Later Han is a case in point. His assault failed, and he told his officers: “The rebels are surrounded on all sides, so they are fighting to the death. If we lift the siege, they will come out on their own; once they do, their resolve will be scattered and they will be easy to defeat.” Events unfolded just as he said. Cao Cao’s siege of Huguan is another example. He declared that everyone would be buried alive if the city fell, but repeated assaults failed. Cao Ren told him: “When besieging a city, one must show a way to live. Now you have promised certain death, so they will defend themselves as individuals. This is no plan.” Cao Cao followed his advice and soon captured the city. These are all examples of the same principle.

“Do not press a desperate enemy” means that an army already trapped with no way out should not be pressed too hard.

Du Mu gives the example of Wu’s campaign against Chu during the Spring and Autumn period. After the Chu army was defeated and fled to the Qingfa area, King Helü of Wu wanted to pursue it. King Fuga said, “Even a cornered beast will fight to the death. How much more so a human being? If they know they have nowhere to flee and can only fight to the death, they will surely inflict heavy losses on our army. We should wait until they are halfway across the river before attacking.” Helü took his advice and won another battle.

During the reign of Emperor Xuan of Han, Zhao Chongguo campaigned against the Xianling Qiang. When the Qiang saw the imperial army approaching, they abandoned their baggage and tried to cross the Huang River, but the route was narrow. Chongguo advanced slowly, driving them forward. Some complained that he was moving too slowly and missing the chance to strike. Chongguo said, “These are desperate enemies; we must not press them too hard. If we give them time, they will think only of escaping. If we drive them into a corner, they will turn back and fight to the death.” The generals agreed. As expected, the Qiang rushed to cross the river; tens of thousands drowned, and their army was thoroughly defeated.

Chen Hao says: “A bird driven into a corner will peck; an animal pushed too far will bite.” Mei Yaochen likewise says: “A cornered beast will still fight”—this is only natural.

He Shi cites the case of Lü Hu of Former Yan, who held Ye-wang and secretly conspired with Eastern Jin. After the plot was exposed, Murong Ke and others led an army to attack him. The general Fu Yan advised an immediate assault, saying that Hu was a desperate enemy who had hastily assembled his forces. Once the imperial army arrived, morale would collapse throughout his ranks, so a swift battle would save time and resources. Murong Ke, however, judged that Hu was a seasoned rebel, skilled at preparing defenses. He advised surrounding the city and waiting until its provisions ran out and outside aid was cut off; within a hundred days, he said, it would surely fall. There was no need to trade soldiers’ lives for a short-lived advantage when victory could be won without bloodshed. The army therefore maintained a long siege for six months. Ye-wang fell, Hu fled south to Jin, and all his troops surrendered.

During the Five Dynasties, the Jin generals Fu Yanqing and Du Chongwei encountered the Khitan at Yangcheng on the northern frontier. About a hundred thousand Khitan horsemen surrounded the Jin army in open country. The army ran short of water. The soldiers dug wells and wrung muddy water to drink, and many people and horses died of thirst. Yanqing said, “Rather than surrender helplessly, we should give our lives for the state. We are already at the very limits of hardship.” He led the elite cavalry out to attack. A strong wind happened to raise clouds of dust, and they seized the moment to fight decisively. The Khitan were routed. In this case, Yanqing’s army, surrounded by a hundred thousand troops, was desperate and fighting to survive. The Khitan failed to understand this and were defeated.

Zhang Yu says: “If the enemy burns its boats and smashes its cooking pots, resolving to fight to the death, it must not be pressed—for when reduced to extremity, it will fight back.” Another example comes from the Jin defeat of Qi at An. When the Marquis of Qi asked for a truce, the Jin refused. The Marquis of Qi said, “Let me gather the remnants of my troops and fight one more time with our backs to the city.” The Jin feared this and agreed to make peace.

The principle expressed by King Fuga of Wu—that a cornered beast will fight—and Zhao Chongguo’s point that giving desperate enemies time makes them flee without looking back, while pressing them hard makes them turn and fight to the death, are much the same.

In sum, a desperate enemy should be left a way out and given room to act, or surrounded without being pressed until it collapses on its own. Pressing it relentlessly can provoke a last-ditch counterattack and bring heavy losses in return.

The Annotations to Sunzi, Volume Eight: “The Nine Changes” (Opening)

How different commentators explain “the Nine Changes”

Cao Cao says: Changing one’s usual methods of warfare and choosing an appropriate approach in each of nine situations is what is meant by “the Nine Changes.”

Wang Xi says: “Nine” is the limit of number; in warfare, one must carry the art of adapting to the utmost. An old poem speaks of “nine changes returning to the thread.” It is unclear which specific nine situations Cao Cao had in mind. Some also say the phrase refers to adapting to nine kinds of terrain.

Zhang Yu says: “Change” means not clinging to customary methods, but responding flexibly to circumstances and choosing what is appropriate to the time and place. Whenever one contests advantage with an opponent, one must understand the nine kinds of change. That is why “The Nine Changes” follows “Contending for Advantage.”

The general meaning of Sunzi’s original text

Sunzi says: The general principles of warfare are these: a general receives orders from the ruler, gathers the army and assembles the people, and then sets out on campaign.

Zhang Yu says: This was already discussed above, so it is not repeated here.

Do not encamp on broken terrain: On “broken terrain,” where travel is difficult and one can easily be trapped—such as ground that is uneven, muddy, or obstructed—do not set up camp and remain there for long.

Impassable Ground: Do Not Encamp

Cao Cao says: There is nowhere to rely on. A place washed away by water is called impassable ground. Li Quan says: Low-lying terrain is called impassable ground; an army marching there will inevitably be flooded. Chen Hao says: Impassable ground is low-lying terrain. Zhuge Liang calls it “the land of the underworld”: high on all sides and low in the middle, like being trapped in a prison. Meng Shi says: Terrain that is too low leaves an army vulnerable to being surrounded by the enemy. Du You says: When choosing a place to station troops, seek advantage and avoid danger. Mei Yaochen says: Places such as mountain forests, rugged terrain, and marshes are not suitable for a long stay, because there is nowhere to rely on. He Shi says: The next section says that on impassable ground one should quickly find a way out; it refers to low-lying, dangerous terrain that should not be held. Zhang Yu says: Difficult routes such as mountain forests, rugged terrain, and marshes all count as impassable ground. Since there is nowhere to rely on, one must not camp there.

Convergent Ground: Forge Alliances

Cao Cao says: You must form ties with the feudal lords. Li Quan says: A place with roads leading in all directions is called convergent ground; it lies where the territories of different states meet. Jia Lin says: You should ally with the feudal lords and secure outside support. Mei Yaochen says: A place with routes in all directions connects to neighboring states, so you should cultivate ties with local powers. He Shi says: The next section says, “On convergent ground, I would strengthen my alliances,” meaning that agreements with the feudal lords must be firmly secured. Zhang Yu says: Since convergent ground lies near neighboring states, you should first form ties with them, so they can support one another.

Cut-Off Ground: Do Not Remain

Cao Cao says: Do not stay for long. Li Quan says: Ground without springs or wells, grazing, or firewood is called cut-off ground; it is not suitable for holding. Zhang Yu (whose commentary here repeats the one on convergent ground; following the commonly used text, it is understood to refer to cut-off ground) says: On ground where provisions are unavailable and a prolonged defense is impossible, do not remain.

Do Not Remain Long in Desperate Terrain

Cao Cao says: Do not stay in one place for long.

Li Quan says: A place without springs or wells, grazing land, or places to gather firewood is called desperate terrain. You cannot remain there.

Jia Lin says: A narrow, dangerous valley with no way forward is desperate terrain. Leave as quickly as possible; do not delay.

Mei Yaochen says: When you have just crossed the border into another state, the terrain may not yet count as the least severe kind of “easy terrain,” but you still should not stay long.

Zhang Yu says: Leaving your own state and crossing the border to wage war means entering desperate terrain. It is even more dangerous than “deep terrain,” so you must never set up camp there or remain for long.

In Encircled Terrain, Use Strategy

Cao Cao says: Use a stratagem to win through surprise.

Li Quan says: Encircled terrain is dangerous, but there may still be a way through. The key is careful planning.

Jia Lin says: A place surrounded by dangerous terrain is called encircled terrain. The enemy can move about, but we have difficulty entering or leaving. In such a place, prepare an unexpected stratagem in advance so the enemy cannot harm us; only then can we overcome the danger.

Mei Yaochen says: When the routes in and out are dangerous and winding, use a strategy that takes the enemy by surprise.

He says: The next chapter also says, “In encircled terrain, use strategy.” This means that when facing the enemy in a difficult and dangerous place, you must use unusual, risky, and deceptive stratagems to avoid being put at a disadvantage.

Zhang Yu says: Where the front is narrow and the rear is secure, use an unexpected stratagem. For example, when Emperor Gaozu of Han was surrounded by the Xiongnu, he escaped through Chen Ping’s clever stratagem. That is the kind of situation meant here.

In Death Ground, Fight

When you reach “death ground,” where there is no way to retreat and staying means certain danger, you can only fight a decisive battle and seek survival through combat. You can no longer count on maneuvering at ease or holding out for a long time.

Plain-Language Interpretation of Related Passages in Sunzi’s Annotations

Fatal terrain (ground where an army is trapped, with no way forward or back)

Cao Cao says: On this kind of ground, the army must fight to the death.

Li Quan says: Put the army in a position where it has no choice but to fight, and the soldiers will each struggle desperately to survive. Han Xin’s defeat of Zhao is an example.

Mei Yaochen says: With the way blocked both ahead and behind, the army can only fight a decisive battle. These comments explain the general meaning of the “Nine Grounds.” Wang Xi’s notes on the first five kinds of terrain agree with Cao Cao’s.

He says: See the next chapter, “On fatal ground, fight.” On this kind of ground, the only way to survive is to attack quickly and fight to the death. If the army delays and refuses to fight, its morale will fall and its provisions will run out. What else is there to do but die? Zhang Yu says: With nowhere to flee, the army should fight with all its strength. Han Xin of Huaiyin, who formed his ranks with their backs to the river, is an example.

From “On broken ground, do not encamp” to this passage, the subject is the Nine Variations. Only five points are listed, as a broad outline. The “Nine Grounds” chapter discusses “the variations of the Nine Grounds,” but gives details for only six points, also as a broad outline.

The relationship between the Nine Grounds and the Nine Variations

Every kind of terrain has its configuration and its variations—that is, its potential and the need to adapt. The first part of the “Nine Grounds” chapter discusses potential; the second part discusses adaptation. How do we know that the “Nine Variations” means the variations of the Nine Grounds? The passage that follows says that a general who does not understand the Nine Variations cannot gain the advantages of the terrain, even if he knows its features. The “Nine Grounds” chapter also says that the variations of the Nine Grounds and the advantages of yielding and advancing must be carefully examined. This makes the meaning clear. The “Nine Grounds” chapter discusses the Nine Grounds, and this passage discusses the Nine Variations because Sunzi first intends to explain the Five Advantages. He therefore begins with the Nine Variations. The Nine Variations and the Five Advantages must be used together, so they are explained at the same time.

Cao Cao says: Narrow, hazardous terrain is a route one should not take. Only when there is truly no alternative should one proceed, and then one must adapt flexibly.

Li Quan says: Roads have narrow, dangerous stretches where one fears the enemy may be lying in ambush. Such routes should not be taken.

Du Mu says: Emperor Guangwu of the Eastern Han sent Ma Yuan and Geng Shu to subdue the Five Creeks tribes of Wuling. Their army was stationed at Xia Jun (in present-day Chenzhou, Hunan), from which two routes were available. The route through Mount Houtou was shorter but had dangerous waters; the route through Mount Chong was level, but made grain transport more difficult. At first, the emperor hesitated. Once the army arrived, Geng Shu wanted to take the route through Chong, while Ma Yuan thought that would waste provisions. He argued that they should take the route through Houtou instead: once they controlled the enemy’s vital passage, the rebel forces would collapse on their own. The emperor was informed and accepted Ma Yuan’s proposal, so the army advanced through Houtou. The tribesmen held the high ground and guarded the pass, while the currents ran too fast for the boats to advance. The hot, damp weather then brought an epidemic, killing many soldiers; Ma Yuan also fell ill and died in the army. Geng Shu wrote to his elder brother, the Marquis of Haozhi: “I had previously advised attacking the granaries at Chong first. Though transporting supplies would have been difficult, the troops and horses could have been put to use. Tens of thousands of soldiers wanted to attack first. Now we cannot even get through Houtou. The great army is trapped in frustration and will die here. It is truly heartbreaking.”

Jia Lin says: “You” means “from.” When the route is unfavorable, one should not take it, even if it is shorter.

Du You says: Dangerous terrain is a route one should not take. Only when there is no alternative should one proceed, and then one must adapt.

Mei Yaochen says: Avoid narrow, dangerous terrain. Even if it is a shorter route, do not take it.

Wang Xi says: A route may be passable, yet one may still choose not to take it for fear of an ambush. For example, Zhao She advised Zhou Yafu to avoid the narrow, hazardous terrain of the Xiao Pass, where he feared enemy troops might be lying in wait. He recommended taking the route through Lantian and Wuguan to Luoyang; the journey would be only a day or two longer.

Zhang Yu says: In narrow, hazardous terrain, chariots cannot travel side by side and cavalry cannot form ranks, so one should not take such a route. If there is no alternative, one must adapt flexibly. For example, Han Xin knew that Chen Yu had not followed Li Zuoche’s stratagem, and only then dared to enter the Jingxing Pass.

“There are armies that should not be attacked” means that some enemy forces or situations, even when they appear vulnerable, should not be attacked rashly.

Cao Cao says: Even when an army can be sent into battle, if the terrain is difficult and cannot be held for long, staying there will delay a greater opportunity already in hand. Even if the position is taken, the gains will be meager. Soldiers trapped in a desperate situation will often fight to the death.

Du Mu says: This principle is akin to “do not attack elite troops, do not block an army returning home, do not press a desperate enemy, and do not attack troops fighting from a death ground.” Sometimes our forces are strong and the enemy weak, but if the enemy’s vanguard has already arrived, it is still unwise to attack outright, lest the enemy be startled into retreating along the whole front. Explaining these situations in which an army should not be attacked shows that a general must know how to adapt; this is why the topic appears in the “Nine Changes” chapter.

Chen Hao says: If a small gain is not enough to unsettle the enemy, do not attack, lest you exhaust your troops for no result.

Jia Lin says: If the enemy can be subdued through the force of one’s authority and virtue, there is no need to fight them directly. If they are entrenched behind dangerous terrain and would fight to the death if attacked, it is better to hold one’s position and wait for them to slacken before making a move.

Du You, Mei Yaochen, Wang Xi, and others also stress that one should not attack when the terrain is too difficult to occupy for long and offers little gain, or when facing bait troops, elite troops, or a well-ordered formation, or when “going forward brings no advantage.”

Zhang Yu says: If letting the enemy go causes no harm and defeating them brings no gain, there is no need to fight. One should also refrain from attacking when our side is weak and theirs is strong, or when our cause is unjust and theirs is just. When Jin and Chu faced one another, for example, Shi Hui judged that Chu’s government, laws, and rites had not changed, so Jin should not contend with it or raise an army for that purpose. The reasoning is much the same.

In sum, a general must recognize which armies should not be attacked and when not to attack. Only then can they adapt to changing circumstances and avoid needless battles.

Some Cities Should Not Be Attacked

Cao Cao says: Even a small city should not be attacked by force if it is well fortified and has ample supplies. In his day, he gave up attacking Huafei, preserving his forces and advancing deep into Xuzhou, where he captured fourteen counties in succession. Du Mu adds that by not attacking Huafei, Cao Cao was able to enter Xuzhou with his forces intact and take fourteen counties in succession. The general point is this: if the enemy occupies a strategic position, with high walls and abundant provisions, hoping to hold up our army, a direct assault may bring no advantage. Yet refraining from attack could also blunt our momentum. Such a city, then, should not be attacked.

During the reign of Emperor Shundi of the Liu Song dynasty, Shen Youzhi, a commander in Jingzhou, rebelled. He had a strong army, abundant resources, one hundred thousand soldiers, and two thousand armored horses. When his forces reached Yingcheng, the registrar Zang Yin argued: “The circumstances of attack and defense are different. Yingcheng cannot be taken in a matter of days. If we lay siege for a long time without capturing it, our momentum and prestige will suffer. Now we can press forward rapidly with the current, and take our objective in a few days. Since we have already struck at the enemy’s heart, how can Yingcheng defend itself? This is precisely what the Art of War means when it says, ‘There are cities that should not be attacked.’” Shen Youzhi would not listen. Liu Shilong, the governor of Ying Commandery, held the city against him. Shen Youzhi committed his full strength to the assault but failed to take it. His troops scattered, and he fled into the woods and hanged himself.

Emperor Wu of the Northern Zhou planned to send troops to Heyang to attack Qi. Yuwen Bi of the Ministry of Personnel advised him: “When using troops, one must choose the ground carefully. Heyang is a strategic crossroads where elite forces are concentrated. If we attack it with all our strength, we may not achieve our aim. In my view, the bend of the Fen River, where the garrison is stationed on a small, level hill, would be easy to capture. There is no better place to deploy our forces.” Emperor Wu did not heed him, and the campaign achieved nothing. Later, when he launched a large-scale attack on Qi, he finally followed Yuwen Bi’s plan and destroyed Qi.

From the third year of the Yuanhe era of the Tang dynasty until now, thirty years have passed, and the court has launched four campaigns against the rebels: Wei-Bo attacked Nangong County, Shangdang attacked Lincheng County, and Taiyuan attacked Hexing Town. The rebels’ three cities had deep moats and sturdy walls. They kept unending stores of everything needed to defend them, including fodder, grain, rice, stones, metal, charcoal, hemp, and oil. The imperial armies attacked but could not take the cities; their troops were worn down and exhausted. The rebels then sent elite forces to relieve them, and the imperial armies lost every battle. Thus, over thirty years, the strength and resources of the whole realm were squandered in attacking tens of thousands of rebels. Their territory was surrounded on all sides, and even after ten years of fighting in total, not a single inch was gained. This was because the court repeatedly fell into the rebels’ traps and failed to adapt.

Jia Lin says: “A force whose commander is deeply loyal and dutiful, and who has been ordered to hold his position to the death, should not be attacked either.”

Mei Yaochen says: “There is harm in doing so.”

Wang Xi says: “A city that is not a strategic stronghold may still be possible to attack, but one should fear exhausting the troops and blunting their momentum. Or the city may not be especially strong, but its defenders may be ready to die for it. Even if it can be taken within a set time, relief forces may arrive; and even if the city is captured, the gain may not outweigh the harm.”

Zhang Yu says: “If a city can be captured but cannot be held, and leaving it alone poses no threat, there is no need to attack it. Nor should one attack a city with deep moats and high ramparts if it cannot be taken. This is illustrated by the case in which Shi Gai asked to attack Biyang, and Xun Ying replied: ‘The city is small but well fortified. To defeat it would bring no honor; to fail to subdue it would invite ridicule.’”

Plain-Language Interpretation

“There are places one need not contend over.”

Some places are not worth fighting for.

Cao Cao said: If a place offers little benefit, even if you seize it for a time, you are likely to lose it again. So it is not worth fighting for.

Du Mu said: Such a place is hard to hold, and losing it is no great loss.

When Wu Zixu advised Fuchai, king of Wu, he said: If we attack Qi now, even if we take its land, it will be like a stony field—it yields no grain, cannot be held, and is of no use.

During the Eastern Jin, Tao Kan was stationed at Wuchang. Some proposed dividing the troops and stationing them at Zhucheng, on the north bank of the Yangtze. Tao Kan repeatedly refused, but the debate continued. He crossed the river to hunt, then summoned his generals and said: “I rely on the Yangtze River as a natural barrier against the enemy. Zhucheng lies on the north bank, with no support nearby and foreign tribes on its borders. Those tribes covet profit, while the Jin people make demands of them. Unable to bear it, they will surely bring outside enemies into our territory. That would be inviting disaster, not resisting the enemy. Even if we station troops there now, it will do Jiangnan no good. If northern enemies find an opening, Zhucheng will be of no help.” Later, Yu Liang insisted on garrisoning Zhucheng, and the result was indeed a crushing defeat.

Mei Yaochen said: It means a place that offers no real benefit to fight over.

Wang Xi said: If the enemy already holds a strategic position, or if a place you might seize would be of no use or hard to hold, there is no need to fight for it.

Zhang Yu said: If taking a place hinders military operations, while losing it does no harm to you, there is no need to fight for it. The same applies to remote places: even if you take them, you will ultimately find them difficult to hold for long, so they should not be fought over. When Wu Qi attacked Qi, Wu Yuan (Wu Zixu) advised him: Taking land in Qi would be like gaining a stony field; it would be better to deal with Yue sooner. The king of Wu ignored this advice and was eventually destroyed by Yue. This is an example of the same principle.

“There are commands from the ruler that need not be obeyed.”

(This item appears in the original only as a heading. Its specific meaning must be understood in the context of The Art of War as a whole and the various commentators’ notes: on the battlefield, a general may, when necessary, refuse to carry out a ruler’s command that would clearly harm the state or the army, so as to preserve freedom of action in warfare. Since the commentaries here do not elaborate, this is a brief explanation of the heading.)

This passage brings together commentaries by military strategists from different periods on “the Nine Changes” in The Art of War and a commander’s ability to make decisions in the moment. Its general meaning is as follows.

Cao Cao says: If an action benefits the campaign, there is no need to be bound by the ruler’s orders.

Li Quan likewise argues that one should not be bound by the ruler’s orders when doing so would hinder effective action. He cites Rangju’s execution of Zhuang Jia and Wei Jiang’s execution of Yang Gan as precedents: commanders should enforce military discipline and exercise their authority according to the law, without granting leniency out of deference to the ruler’s wishes.

Du Mu quotes the Wei Liaozi: Weapons are instruments of ill omen, and warfare runs counter to Virtue. A commander’s position, meanwhile, is an “office of death”—one serves and accepts responsibility at the cost of one’s life. He adds that above, a commander must not rely solely on Heaven’s Mandate; below, not solely on the advantages of terrain; at the front, not fear the enemy; and behind, not rely solely on the ruler. This emphasizes that commanders must exercise independent judgment on the battlefield.

Jia Lin says: The opportunity to secure victory cannot be left to the ruler’s orders. If it benefits the state, a commander may decide independently.

Meng Shi says: “At the front, no enemy; behind, no ruler” means that matters beyond the city gates—that is, on the battlefield—are for the general to decide.

Mei Yaochen says: The central principle is “act according to what is appropriate.” These five points are collectively called the Five Advantages.

Zhang Yu says: Acting in a way that benefits the campaign, even when it means not following the ruler’s orders, is the same principle as King Kai’s “act on what is right without waiting for orders.” Some hold that the five advantages extend from “There are roads not to take” through this passage, while the Nine Changes extend from “In broken terrain, do not encamp” to “There is terrain over which one does not contend.” None of these nine situations can be referred back to the court for a decision every time; each requires adapting to circumstances. Thus, “There are orders of the ruler that need not be obeyed” summarizes them all.

“Therefore, a commander who understands the advantages of terrain in relation to the Nine Changes knows how to use the army.” This is the sentence that follows: A commander truly understands the use of the army only if they grasp the Nine Changes and the advantages offered by the terrain.

Note: The Nine Changes are nine situations in which Sunzi says military action must be adapted to the terrain and the circumstances. “There are orders of the ruler that need not be obeyed” is Sunzi’s famous principle that a commander in the field has the authority to decide independently as circumstances require, provided the decision benefits the whole army and the state.

How Various Commentators Explain “Nine Changes” in Annotations to The Art of War

Li Quan says that “Nine Changes” refers to the nine matters of military operations discussed in the previous chapter. Du You says these nine matters all require adaptation to circumstances and cannot be handled by rigidly adhering to ordinary rules; that is why they are called “changes.” Jia Lin says that “Nine Changes” means a commander exercising flexibility under nine kinds of circumstances: adapting as situations arise, acting according to advantage, and avoiding fixed routines. Only then can one respond flexibly and suit one’s actions to the terrain. The title speaks of “Nine Changes,” though the related matters number more than nine; whether to obey the ruler’s commands, however, is not governed by fixed rules for what is “ordinary” or what must “change.”

Mei Yaochen says that one must understand the conditions of the nine kinds of terrain and turn disadvantage into advantage; this is what it means to know how to adapt. Wang Xi says that only a wise and capable person can fully grasp the many changes in how things work.

He Shi raises a question: Sunzi titled a chapter “Nine Changes,” yet although more than ten commentators have explained it, few have listed exactly which nine items make up these changes. Why? Comparing the text closely, He Shi argues that the surrounding discussion is mainly about the advantages and disadvantages of different kinds of terrain. Of the ten matters mentioned, “there are commands of the ruler that need not be obeyed” is not about terrain at all, so it belongs to a different category. He Shi understands Sunzi’s meaning as follows: once a general has received orders to lead an expedition and assembled the army, if any of the nine kinds of terrain along the route offer harm without advantage, the general should adapt accordingly. Even if the ruler orders the army to encamp, withdraw, or attack, the general may choose not to comply. The text goes on to say that a general who does not understand the advantages involved in the “Nine Changes” cannot gain the practical benefits of terrain, even if familiar with it. How, then, can the ruler’s commands be weighed in the same calculation as the advantages and disadvantages of terrain? Moreover, the “Terrain” chapter says that if military principles call for an attack but the ruler orders against it, the general should still attack; and if those principles counsel against an attack but the ruler insists on one, the general may refuse. He Shi believes this captures Sunzi’s original intent.

Zhang Yu sums up the point: changing ordinary methods while still securing their advantages is what it means to understand the art of war.

The general meaning of the classic

If a commander cannot understand the various opportunities for victory and advantages of adapting that come from the “Nine Changes,” then even if he knows the terrain, he still cannot gain its advantages. If those who command the army do not understand the method of the Nine Changes, then even if they know ordinary favorable conditions such as the “Five Advantages,” they will not be able to move the hearts of the people or deploy their forces effectively, and will fail to bring human capabilities into play.

Key points from the various commentaries

Jia Lin says: Knowing the terrain but not adapting as circumstances shift will not only prevent one from gaining its advantages, but can also make one vulnerable to harm. That is why a commander’s excellence lies in adapting to the situation.

Mei Yaochen says: If one knows the terrain but not how to adapt, how can one truly gain its advantages?

Zhang Yu says: Terrain has both form and change. Knowing only its features and layout, without understanding how it changes, likewise makes its advantages hard to gain. A commander’s excellence lies in understanding how to adapt. This is in keeping with the Sunzi’s teaching that beyond knowing the terrain, one must also understand the “Nine Changes” and know how to employ people.

Classic: Annotations to Sunzi

Cao Cao says: This refers to the five matters discussed below. Some say “five changes” instead of “nine changes.” Jia Lin says: The five advantages and five changes are all included within the nine changes. When circumstances call for adapting, the advantage remains; if one fails to adapt, the harm often comes from one’s own actions. There is therefore no fixed formula. Only by grasping this principle fully can one speak of employing people appropriately.

The five changes are these: Even if a road is short, do not take it if you know it may be blocked or ambushed. Even if the enemy can be attacked, do not attack if you know they may fight desperately, like trapped beasts. Even if an isolated city can be attacked, do not attack if you know of unforeseen circumstances such as ample provisions, sharp weapons, a wise commander, or loyal ministers. Even if territory can be contested, do not contest it if you know it will be hard to hold once taken, bring no benefit, or be retaken at the cost of your own men. Even if an order from the ruler should be obeyed, do not follow it blindly if you know it will be obstructed from within or bring harm to your own forces. These five changes must be judged according to circumstances; they cannot be fixed in advance.

The five advantages one might covet are these: take the road because it is short; attack because the enemy is weak; assault because the city is in danger; contest the land because it can be seized; accept command because the army can be deployed. If one knows only how to pursue these five advantages and does not understand how to adapt, one will not only fail to employ people well but may also lose the army and lay the soldiers low.

Mei Yaochen says: If one knows only advantage and not how to adapt, how can one employ people? Wang Xi says: To know the advantages of the five kinds of terrain but not how to adapt is like forcing the strings of a zither into fixed positions and trying to play it. Zhang Yu says: In warfare there are advantages and changes. If one knows the advantages but not the changes, how can one put people to good use? The five matters Cao Gong gives below as the five advantages are the five matters under the nine changes; they are not the five matters mixed together under “advantage and harm.”

Therefore, the wise consider affairs by weighing advantage against harm.

Cao Cao says: When there is advantage, consider the harm; when there is harm, consider the advantage. When circumstances call for adapting, adapt. Li Quan says: Consider how to harm the other side and benefit one’s own. Jia Lin says: “Mixed” means, on the one hand, closeness, and on the other, difficulty. The meaning is that advantage and harm are intertwined; in considering affairs, the wise always weigh them together.

Cao Cao says: When things are going in your favor, consider the dangers; when they turn against you, look for the advantages. In difficult situations especially, you must adapt flexibly and use strategy.

Li Quan says: Work out how to harm the enemy and benefit yourself.

Jia Lin says: Advantage and danger are often mixed together; that is the usual state of affairs. Only by weighing them carefully can the wise truly secure an advantage.

Mei Yaochen: His view is the same as Cao Cao’s.

Wang Xi says: When a commander understands the “Nine Changes,” he has grasped the principles of advantage and danger.

Zhang Yu says: When the wise take action, even if they have the advantage, they first consider what harm might follow. Even if they are at a disadvantage, they first look for what advantage it might contain. This is what it means to “understand change.”

Original: Mix in considerations of advantage, and your undertakings can be trusted.

Cao Cao says: When calculating against the enemy, do not let him use the five kinds of terrain to harm you. Only then can your own undertakings be trusted and carried out successfully.

Du Mu says: “Trusted” means that something can truly be put into practice. If you want to gain an advantage over the enemy, do not look only at what benefits you. First include in your calculations the ways the enemy might harm you. Only after weighing both sides can you be confident that your plans are sound and will succeed.

Jia Lin says: When gaining an advantage, consider the dangers as a check on yourself. Another interpretation is: consider danger and advantage together when acting, enforce your orders with authority, punish violations under the law, and do not waver in your decisions. Then your undertakings can be trusted, and your subordinates will not dare deceive you.

Mei Yaochen says: Weigh the possible dangers against the advantages, and your undertakings can be carried out.

Wang Xi says: Put your advantage to full use, and you can prevail. (Note: Some commentaries give a different reading of this sentence.)

Zhang Yu says: Weigh possible dangers against the advantages you seek, and your plans can be carried forward. When Zheng defeated Cai, the people of Zheng were all pleased. Only Zichan was worried. He said, “A small state that lacks virtue in civil affairs but has military success faces no greater danger than this.” Later, Chu did indeed attack Zheng. This is an example of “considering danger when things go well.”

Original: Mix in considerations of danger, and troubles can be resolved.

Plain-language explanation: When you are at a disadvantage or facing trouble, also take into account any advantages that might emerge from the situation. This makes it easier to dispel your concerns and escape the impasse before you. The sentence pairs with the one above: when seeking advantage, include vigilance about danger so your undertakings can be trusted; when facing danger, look for possible advantages so your troubles can be resolved. Both express the idea behind the “Nine Changes”: weigh circumstances according to how they unfold, and do not cling to a single fixed approach.

A Plain-Language Commentary on Sunzi

Cao Cao says: When calculating what is advantageous, one must also consider what is harmful. Even in the face of disaster, one can find a way to resolve it.

Li Quan says: When wise people deal with advantage and harm, they always act in accord with the Great Dao. They do not drive matters to extremes.

Du Mu says: If you want to break an enemy’s predicament, you cannot look only at how the enemy might harm you. First consider what benefit you might gain from the enemy, weigh advantage and harm together, and then decide how to resolve the danger. That is why the passage above says: “The wise, in their deliberations, always consider both advantage and harm.” For example, if the enemy has surrounded us, thinking only of breaking out and fleeing can weaken morale and make us more vulnerable to pursuit. It is better to spur the soldiers to fight their way out, using the advantage of victory to lift the siege. One example can be extended to others.

Jia Lin says: When facing harm, consider how to use advantage to avoid it. The principle behind “placing the army on ground where it must face death, and it survives; throwing it into a place where it seems doomed, and it endures” is that disaster can be turned aside.

Mei Yaochen says: If you weigh harm against advantage, you can escape disaster.

Wang Xi says: If you think through the dangers thoroughly, you will not be defeated.

He says: Advantage and harm give rise to one another and complete one another. Clear-sighted people always reflect carefully on both.

Zhang Yu says: Compare the advantage you might gain with the harm you might suffer, and you can resolve the danger facing you. For example, when Zhang Fang attacked Luoyang, he lost battle after battle. Someone urged him to flee under cover of night. Zhang Fang replied: “The balance of strength in war is always changing. What matters is being able to turn defeat into victory.” He secretly advanced on the enemy by night and eventually won. This is an example of thinking about advantage when faced with harm.

Therefore, to make the feudal lords submit, one may restrain them through harm; to make them come over, one may attract them with advantage. (Read together with the later phrase “make the feudal lords submit through harm,” this means that both coercion and inducement are used, and that advantage and harm must always be considered together.)

Commentary on the Sunzi: Related Passages

Cao Cao says: The key is what the enemy fears and most wants to avoid.

Li Quan says: The key is their political affairs and the foundations of their rule.

Du Mu says: Here, “hate” is pronounced wù and means to loathe or fear. The point is that if the enemy has something they particularly fear or consider taboo, we should seize the opportunity to exploit it and inflict harm. By not letting the moment pass, we can force the enemy to submit.

Jia Lin says: There is more than one way to use “harm” as a means of dealing with the enemy. We can spread slander about their worthy ministers, leaving them with no one capable to serve; send agents to infiltrate and disrupt their policies; use deceit to sow discord between ruler and ministers; send them finely crafted objects to drain their people and resources; encourage debauchery and corrupt their customs; or present beautiful women to distract the ruler. If these things are planned in secret and kept under tight guard, they can all damage the other side and make it yield.

Mei Yaochen says: Constrain them in ways that damage their interests, and they will submit.

Wang Xi says: Drive the enemy into a place where harm is certain and escape is difficult. Give them no chance to get out of it.

Zhang Yu says: Lure the enemy into a situation where they will suffer harm, and they will submit of their own accord. Another view is that sowing mutual suspicion between ruler and ministers, and exhausting the people and draining their resources until they lose their livelihoods, are all methods of “harm.” Wei Xiaokuan’s sowing of discord around the Northern Qi general Hulü Guang, and Gao Jiong’s strategy for pacifying Chen, are examples of this kind.

“To set the feudal lords to work through affairs”

Cao Cao says: “Work” refers to tasks and undertakings. The meaning is to make the feudal lords submit and obey by setting them to work (or: to keep them occupied and bring them into submission through major undertakings and practical affairs).

Cao Cao says: “Affairs” means matters and undertakings. Make the enemy toil: when they come in, we go out; when they go out, we come in, wearing them down through constant movement. Li Quan says: What is made to toil is their farming. Du Mu says: Use labor and burdens to wear down the enemy and give them no rest. But our side must first have a firm foundation—troops, a prosperous state, harmony among the people, and effective orders—before we can do this. Du You says: Use all kinds of tasks and forced labor to keep the rulers and people of other states from living at ease, as when Han made Qin dig canals. Mei Yaochen says: Stir up the enemy with affairs, and they will grow weary. Wang Xi says: Some commentators take this to mean continually making a show of preparing to attack, thereby exhausting the enemy. It is like Tian Chang’s remark: “Our offensive has already been brought to bear on Lu.” Zhang Yu says: Burden the other side with affairs and labor so that they get no rest. Another interpretation is to bring the strength and prosperity of one’s undertakings to bear, thereby gaining power over other states—as when Zheng, faced with the might of Jin and Chu, hurried to serve them with sacrificial offerings and silk.

“Make the feudal lords hasten to us with profit” means that the way to draw the feudal lords swiftly to our side is through advantage.

Cao Cao says: Make them come of their own accord and submit. Li Quan says: Entice them with advantage. Du Mu says: Tempt them with a small gain, so they come willingly to our side and fall into our plans. Meng Shi says: “Hasten” means to move quickly. Skillfully display an advantage so that the other side forgets the changing situation and rushes to us; then use changes to constrain them. This, too, is what it means to make good use of human effort. Mei Yaochen agrees with Du Mu. Wang Xi says: In maneuvering between enemy and ally, carefully calculate our own advantage at every turn. Zhang Yu says: Move the other side with a small gain so that they are sure to come over.

“Therefore, the conduct of war does not rely on the enemy’s not coming, but on our own readiness to receive them.” The principle of warfare is not to count on the enemy staying away, but to count on our own preparations and ability to respond at any moment.

Mei Yaochen says: What we rely on is unremitting diligence.

“It does not rely on the enemy’s not attacking, but on our own position being impossible to attack.” We should not count on the enemy refraining from an assault, but on having defenses that they cannot breach.

Cao Cao says: Be mindful of danger in times of security, and remain prepared without slackening. Li Quan says: Defense must never be neglected. Du You says: In peaceful times, our side is already prepared for what may come.

Mei Yaochen says: What is meant by “having something to rely on” is never letting up.

Do not count on the enemy not attacking. Rely instead on having no weakness that can be exploited.

Cao Cao says: In times of peace, do not forget danger; remain prepared at all times.

Li Quan says: There must be no gap in one’s defenses.

Du You says: In security, consider danger; while a state endures, consider its downfall. Constant readiness is the way to lasting security.

Mei Yaochen says: What one relies on is preparedness.

Wang Xi says: “Preparedness” must be put into practice.

He Shi cites the Wu Lue: A gentleman carries weapons even in times of peace. In ancient times, when feudal lords met, their guards stayed close at hand; whenever there were civil affairs, there were also military preparations. How much more so when defending the borders against an enemy, with blades and spears at the ready? Armies often win by striking where the enemy is weak and attacking when it is unprepared. If defenses are orderly and complete, the enemy will find it difficult to act. The Zuo Commentary says: “Without preparation and forethought, one must not send out an army.” Long ago, when Jin resisted Qin, it dug deep moats, raised high ramparts, and put its forces in readiness; Qin’s army could not remain for long. When Chu drew up its forces and Wu arrived, Wu saw that Chu was prepared and withdrew.

As a general, Cheng Buxi kept his troops and ranks in strict order when encamped. Within the camp, the alarm clappers were sounded and officials kept the military registers, so the enemy dared not intrude. As military adviser, Zhu Ran continued to beat the war drums morning and evening even when all was peaceful. Everyone in the camp stayed armed and in formation, leaving the enemy unsure where the defenses lay. As a result, whenever Zhu Ran took the field, he often won battles. This is how one can resist aggression from outside.

To remain mindful of danger in times of security, and of disorder in times of order; to be alert before trouble shows itself and to take precautions before disaster arises—this is the highest good. Decisions should be made with strategic terrain in mind; routes and gathering points should be clearly understood; sentry posts should be well defined; defensive lines should be secure; and trenches and fortifications should be maintained. One should also increase military supplies or strengthen equipment as needed. Thus it is said: “Before a matter takes outward form, guard against it before it comes to pass”—this too is the highest good. It is also said: “If preparations are not complete in ordinary times, one cannot respond to sudden changes. Be prepared for every eventuality, and there will be no trouble.” Keep the enemy weary while you remain rested, and let them grow old while you stay strong. This is called seizing the enemy’s will first: without fighting, one makes the enemy’s forces submit.

The opposite examples are warnings: Ju collapsed because it relied on its remote and difficult terrain; Qi was destroyed because it underestimated its enemy; Guo perished because it treated Jin lightly; Lu was defeated because it underestimated Zhu; Mo’ao looked down on Luo and let his forces fall into disorder; and the Wu commander entered Chao, advancing recklessly out of overconfidence. These all serve as lessons. Thus, “I have means to meet the enemy” and “I have made myself impossible to attack” refer to being able to prepare in advance.

Zhang Yu says: One must anticipate danger and take precautions. The Zuo Commentary says: “Without preparation for the unforeseen, one must not send out an army.”

There are five dangers for a general

In warfare, there are five dangerous dispositions or weaknesses that can easily lead a general to defeat. The following are the five.

One who is bent on death can be killed

A general who relies solely on courage and is determined to fight to the death, without understanding how to adapt or weigh his options, can be lured into a dead end and destroyed.

Li Quan and Zhang Yu explain that what follows is a discussion of these five dangers. Cao Cao says that a brave but unwise man who seeks only a fight to the death and refuses to yield cannot be held in check through direct engagement. Instead, ambush troops can lure him into a trap and kill him. Li Quan calls this “courage without wisdom.” Du You says that a general who is foolish yet fond of bravery is a menace. Huang Shigong, an ancient military writer, says that the brave like to act on impulse, while the foolish disregard the consequences for gain, loss, life, and death. Wu Qi, a renowned general of the Warring States period, says that people often judge a general by whether he is fierce, but courage accounts for only a small part of a general’s qualities. The brave are prone to rash action, and rashness blinds them to the consequences; such men should not be appointed. Mei Yaochen agrees with Li Quan. He Shi cites the Sima Fa: the teaching that one should “strive to be first even at the cost of death” concerns the failure to win, and stresses that victory depends on strategy rather than fighting recklessly. Zhang Yu likewise says that a brave but unwise man bent on fighting to the death should not be met head-on; ambush troops should draw out his death wish and kill him. The Sima Fa’s phrase “the superior dies, yet does not win” refers to a general with no plan who knows only how to lead a suicidal charge—and ultimately cannot prevail.

One who is bent on survival can be captured

Another kind of general is so intent on preserving his life and seeking safety at every turn that he fears death. Such a man can easily be surrounded, forced into submission, and captured.

Hesitant and fearful, they can be captured.

Cao Cao says: When they see an opportunity for gain, they fear military law and dare not advance. Li Quan says: An enemy who hesitates and lacks courage can be captured. Du Mu says: The Eastern Jin general Liu Yu pursued Huan Xuan along the Yangtze and fought him at Zhengrong Islet. The rebel army had only a few thousand men, while Huan Xuan’s forces were strong. But Huan Xuan feared defeat and kept small, light boats ready beside his warships, so most of his men had little will to fight. The rebel army used the wind to set fires and pressed forward with all their strength; Huan Xuan’s army was consequently routed. Meng says: If a general is timid, thinks only of retreat, and is unwilling to fight in person, his soldiers will not be elite troops. When both officers and men hesitate, one can attack swiftly and win. The New Instructions say: A general is cowardly if he sees an advantage but cannot advance. The Taigong says: Losing ground and missing an opportunity can bring disaster in their wake. Mei Yaochen says: Timid and indecisive. Wang Xi says: Without the will to fight. Cao Cao says: They see an advantage but are too timid to advance. Wang Xi adds that they will also flee at the first sign of danger. He says: The Sima Fa states, “Excessive suspicion breeds many doubts”; suspicion is a grave danger. Zhang Yu says: If they are afraid in the face of battle and think only of returning alive, one should raise a great clamor and attack while the momentum is with you; they can be captured. When Jin and Chu fought, the Jin general Zhao Yingqi had his men prepare boats by the river in advance, intending to cross first if they were defeated. This is just such a case.

Quick-tempered and prone to anger, they can be provoked with insults.

Cao Cao says: A quick-tempered person can be provoked with anger and insults; he is sure to fall into the trap. Li Quan says: A quick-tempered person has a fierce nature and will lose control when mocked. Tang Taizong’s killing of Song Laosheng and pacification of Huoyi is an example of this. Du Mu says: Those who are easily angered and quick-tempered can be exploited by taunting them.

This commentary discusses a principle of warfare in The Art of War: when facing an enemy general who is impatient, fierce, and quick to anger, one can provoke or insult him to induce rash action, then seize the opportunity to defeat him. Commentators illustrate the principle with historical examples.

Cao Cao says that a hot-tempered person can be deliberately provoked and insulted, and will most likely be unable to contain himself.

Li Quan says that the impatient and fierce are hard by nature, yet cannot withstand public humiliation; once insulted, they are apt to lose their composure. As an example, he cites Tang Taizong, who at the time was still the Prince of Jin, defeating and killing Song Laosheng near Huoyi. The point is that against this kind of opponent, stoking his anger and disrupting his plans often works.

Du Mu explains the terms: “fen” means fierce anger and a tendency to take offense; “su” means narrow and impatient, lacking steadiness and composure. If an enemy commander has these traits, one can insult and provoke him into advancing recklessly and engaging in battle, then defeat him. Du Mu cites an episode from the Sixteen Kingdoms period. Yao Xiang was defending Huangluo, and Fu Sheng of Former Qin sent Fu Huangmei and Deng Qiang to attack him. Yao Xiang dug deep moats, built high ramparts, and held his position without coming out to fight. Deng Qiang advised Fu Huangmei: “Yao Xiang is fierce and hard-natured; we should provoke him by showing our own force. If we march straight ahead, beating drums as we go, and press directly against his camp, he will become enraged and come out to fight. We can capture him in a single battle.” Fu Huangmei followed this advice. Yao Xiang indeed came out in anger and was killed.

Du You says that an impatient person can be roused to anger and made to fight to the death. Someone who is quick to anger, impetuous, and heedless of consequences can be induced to act rashly through taunting gestures.

Mei Yaochen says that an impetuous temperament is especially easy to stir.

Wang Xi says that a general should be valued for his steadiness. If he is personally prone to anger and impatience, others can easily unsettle and control him.

Zhang Yu says that a stubborn and impatient general can be insulted and brought to heel. For example, Ziyu of Chu was fierce and quick to anger. The people of Jin deliberately detained his envoy to provoke him. Ziyu, as expected, angrily pursued the Jin army and suffered a crushing defeat.

The final phrase, “One who is upright can be shamed,” states another weakness of enemy commanders identified by Sun Tzu: a person who is honest and protective of his reputation can be provoked by insults and slander, so that indignation or a refusal to endure humiliation drives him to act rashly. This follows the same principle as “the impatient can be angered” above: adapt one’s methods to the enemy’s temperament and use it to control him. The commentary here only briefly mentions “an upright person”; in transmitted editions, Cao Cao’s and other commentators’ fuller explanations often follow later. Their general meaning is that one who prizes his reputation will act when shamed.

Cao Cao says: A person who is upright and cherishes his reputation can be provoked into action through insult.

Li Quan says: A proud and impatient person can be angered by humiliation.

Du You says: This means that if the enemy is relying on high walls and deep moats, hoping to wear down our army, while our forces cannot afford to stay for long, we should fight quickly. If we judge that the opposing general is quick to anger, we should provoke him with contempt and insult. If he is naturally upright and values his reputation, we should stir him by disgracing him. For example, Zhuge Liang (Zhuge Kongming) once sent Sima Yi (Sima Zhongda) women’s clothing, hoping to enrage him and force him to fight. Zhongda was furious and wanted to cross the Wei River and advance, but Emperor Ming of Wei sent Xin Pi with a tally of authority to restrain him. Even a man of Zhongda’s ability could not suppress his anger—how much less could an ordinary person? Mei Yaochen says: This refers to someone who cares only about reputation and not about consequences. Wang Xi’s view is close to Cao Cao’s commentary.

Zhang Yu says: A general who cares for the people and keeps himself upright can be thrown off balance by defilement and humiliation, causing him to make mistakes.

(Another interpretation of the original meaning:) Someone who cares for his people can be thrown into confusion by being harried and burdened.

Cao Cao says: “If the enemy sends troops to rescue a place they are bound to protect, a general who cares for his people will hurry there day and night to provide relief. Such rescue efforts can wear the enemy down with relentless marching.”

Li Quan says: “Attack what the enemy values, and they will travel light and hurry to its aid. By conserving our own troops and horses, we can use stratagems to exhaust the enemy.”

Du Mu says: “A humane person fears causing death and injury. Unable to weigh one thing against another and abandon one to gain the other, and failing to assess distance and strength, they will come to the rescue wherever we attack. In this way we can wear them down, then defeat them once they are exhausted.”

Chen Hao says: “Some places must be rescued; others need not be. Xiang Yu’s rescue of Zhao was necessary, but the Deputy Father, Fan Zeng, did not need to rescue the King of Liang.”

Jia Lin says: “The upright dislike plundering, and the humane dislike fighting. If they are provoked and harried, their actions will surely fail.”

Mei Yaochen says: “When strength is exhausted, they are worn down.”

Wang Xi says: “Use surprise forces to feint an attack on a city. If the enemy cares for its people, they will repeatedly come to the rescue and be worn down.”

Zhang Yu says: “Though the people are worthy of care, one must weigh benefits and harms carefully. If the enemy never fails to rescue even the smallest place and never leaves a distant one unaided, attack the place they are bound to rush toward, and wear them down until they are exhausted.”

These five circumstances all involve a general’s mistakes and are hazards in the use of troops.

On the March

Cao Cao says: Choose favorable conditions when marching.

Wang Xi says: In marching, rely on the advantages of the terrain and observe the enemy’s situation.

Zhang Yu says: Only by understanding changes in the situation, such as the “nine variations,” can one choose favorable conditions for marching. That is why “On the March” follows “The Nine Variations.”

Sunzi says: Whenever you deploy an army and observe the enemy…

Cao Cao says: Choose a convenient route and advance.

Wang Xi says: When marching, take advantage of the terrain and observe the enemy’s situation.

Zhang Yu says: Once you understand how the nine types of terrain vary, you can choose favorable conditions for marching. That is why this chapter follows “The Nine Variations.”

Sunzi says: Whenever you position your army and assess the enemy…

The opening of Volume Nine continues the discussion of the “five dangers” at the end of Volume Eight: a general’s qualities are best when all five virtues are present, and the conduct of war requires recognizing the five dangers and five prohibitions. Volume Nine turns to choosing terrain for the march and methods of observing the enemy.

Wang Xi says that there are broadly four kinds of terrain for an army to camp in, and thirty-one points to consider when assessing the enemy. Zhang Yu says that the passage from “crossing mountainous terrain and keeping close to valleys” to choosing “a place to hide spies” concerns how an army should be stationed. The passage from observing “an approaching enemy army that remains quiet” to “be sure to examine the situation carefully” concerns how to assess the enemy. “Assess” means to observe and judge.

Cross mountainous terrain and keep close to valleys.

Cao Cao says to stay near places with plentiful water and grass and room to maneuver. Li Quan says that when Sunzi speaks of the “army,” he means our own forces, and when he speaks of the “enemy,” he means the opposing forces. By observing the terrain on which each side relies, one can judge the prospects for victory and the relative positions of the two sides. “Crossing mountainous terrain” means passing through difficult, strategic ground; “keeping close to valleys” means drawing near to water and grass. When setting up camp, first send troops to guard the passes, then let the animals graze and gather firewood. Only then can the army camp securely.

Du Mu says that “cross” means to pass through, while “rely on” means to stay close to. The saying means that when marching through steep, difficult terrain, an army should keep near a valley to make use of its plentiful water and grass. The Master Wu says not to camp directly in front of a valley entrance. An army may stay near a valley, but should not block its entrance.

Jia Lin says that when two armies face each other, each should choose advantageous terrain before acting. “Cross the mountains” means to pass over or across them; “rely on the valley” means to stay beside it. Crossing the mountains avoids leaving a threat to the rear, while staying near a valley provides access to water and grass. Mei Yaochen says that if mountains obstruct the way ahead, an army should use a valley as a defensive barrier.

Wang Xi says that “cross” means to pass over, while “rely on” means to stay close to. Cao Cao likewise advises staying near places with plentiful water and grass and room to maneuver. Zhang Yu says that “cross” also means to pass over. After crossing steep mountains, an army should camp near a valley: this lets it make use of water and grass and rely on the strategic terrain to strengthen its defenses.

Zhang Yu gives an example from the Eastern Han to illustrate this point. When the Qiang people of Wudu rebelled, Ma Yuan went to suppress them. The Qiang occupied the mountains, while Ma Yuan took the advantageous ground and controlled the water and grass, refusing to engage them in battle. Short of water and provisions, the Qiang were driven into hardship and eventually surrendered in full. Zhang Yu argues that they failed to understand the importance of staying near valleys to gain access to water and grass.

Choose a place with water that is suitable for camping, and occupy the high ground.

【Classic】Annotations on The Art of War

Modern interpretation

Cao Cao says: “Life” refers to a direction facing the sun, where one receives Yang Qi.

Li Quan says: Facing the sun is called “life”; in the mountains, this means occupying high ground. A place that is both favorable and elevated is suitable for setting up camp.

Du Mu says: The army should occupy high ground and face south, toward the sun.

Chen Hao asks: If the terrain runs east to west, which direction should one face? The answer: Face east.

Jia Lin says: Occupying a sunny position is called “life.” “Looking toward life” means having open, unobstructed ground ahead. The army should be stationed on high ground.

Du You says: High ground is Yang. “Looking” means having terrain ahead that allows one to survive and move freely. The army should be stationed at a height.

Mei Yaochen says: On hills, one should settle on the sunny side; high ground makes it easier to take advantage of the terrain.

Zhang Yu says: “Looking toward life” means facing the sunny side. The army should be stationed on a high, level slope.

“When fighting on high ground, do not climb to meet the enemy” means that when engaging an enemy positioned above, one must not attack uphill.

Cao Cao says: Do not confront an enemy descending from high ground. (This differs from the common reading of the line as “do not climb to attack the enemy”; the commentaries vary.)

Li Quan says: When the enemy comes down from high ground, do not climb up to fight them.

Du Mu says: “High” means elevated. When the enemy is above, do not confront them by attacking uphill. Another reading has “When fighting a descending enemy, do not climb to meet them”: “descending” means coming down. This refers to fighting below a mountain when the enemy tries to lure one uphill; do not climb in pursuit.

Jia Lin says: In battle, it is advantageous to occupy lower ground and strike upward; do not confront an enemy on high ground.

Du You says: Do not confront an enemy on high ground. If you are below a mountain and the enemy draws you uphill, do not climb in pursuit.

Mei Yaochen says: If the enemy occupies high ground, do not climb up to fight them.

Zhang Yu says: If the enemy holds elevated ground, do not climb up to meet them. One version reads, “When fighting a descending enemy, do not climb up to meet them.” This refers to an enemy coming down the mountain to fight and trying to lure you uphill; do not climb up to engage them.

These are the main points for stationing troops and fighting in mountainous terrain.

Mei Yaochen and Zhang Yu summarize: When taking up a defensive position against the enemy in the mountains, follow these principles. Any high and steep terrain is called a mountain.

“When crossing water, keep well away from it” means that when camping beside water, one must keep a distance from the water’s edge. (Do not camp right beside the water, lest the army be trapped by rising water or caught in a surprise attack.)

Cao Cao and Li Quan say: Lure the enemy toward you and make them cross the river.

Du Mu gives an example: When the Wei general Guo Huai was stationed in Hanzhong, the ruler of Shu, Liu Bei, planned to cross the Han River and attack. The generals discussed the matter. Believing their forces were outnumbered, they planned to form up along the river and hold the enemy back. Guo Huai said, “That would make us appear weak, and we would not blunt the enemy’s advance. It would be better to form our lines some distance from the river and lure the enemy across. Once they are halfway over, we can strike, and Liu Bei can be defeated.” After the troops took up their positions, Liu Bei became suspicious and did not dare to cross.

Mei Yaochen says: When a river lies in the way, form your lines some distance from it and lure the enemy across.

Wang Xi says: We are the side forming up with a river behind us—or between us and the enemy—so Cao Cao and Li Quan are right.

Zhang Yu says: When an army crosses a river to camp on the far bank, it should set up camp some distance from the water. This both lures the enemy across and allows room to advance or withdraw. Guo Huai formed his lines away from the river, and Liu Bei saw through the plan and did not cross. That is the point.

Meaning of the original text: When the enemy approaches across a river, do not engage them in the water. Let them cross halfway before attacking; this is to your advantage.

Zhang Yu (repeating the point in a later passage): When an army crosses a river to camp, it should stay some distance from the water, both to lure the enemy across and to keep its options open for advancing or withdrawing. Guo Huai formed his lines away from the river, and Liu Bei understood the plan and did not cross. This is an example of the tactic.

This passage comments on a strategy in The Art of War: attacking an enemy as it crosses a river, when only part of its force has made it across. The military writers of later dynasties explain it in plain language as follows.

Li Quan says that Han Xin used this tactic to kill Long Ju by the Wei River, and that Fuga defeated the Chu army at Qingfa in the same way.

Du Mu says that during the standoff between Chu and Han, Xiang Yu went in person to attack Peng Yue and left the Grand Marshal Cao Jiu to defend Chenggao. The Han army repeatedly challenged him, and Cao Jiu crossed the Si River to engage. The Han army waited until half his force had crossed before attacking, and routed the Chu army. The phrase “within the water” in the original text should actually read “at the river’s edge” or “at the ford”; later writers mistakenly changed the character for “edge” to the one for “within.”

Mei Yaochen says that when an enemy first arrives, trying to stop it directly at the river often cannot prevent it from crossing. Instead, one should lay an ambush at a suitable spot along the bank and attack from there, so the enemy will hesitate to cross. But if one waits too far from the river, the opportunity will pass. The key is to judge the distance carefully.

Wang Xi says that “within” should read “at the river’s edge.” Attacking at the ford will make the enemy hesitate to cross; wait too far from the river, and the advantage is lost. One must find the right distance.

He Shi gives several examples. In the battle of Hongshui between Song and Chu, recorded in the Spring and Autumn Annals, the Chu army had not finished crossing when the marshal urged the Song ruler to attack, but the ruler refused. After the Chu army had crossed but had not yet formed ranks, the marshal urged him again, and he still refused. Only once the Chu army had formed up did the Song army attack. It was routed; the Song ruler was wounded in the thigh, and all his palace guards were killed. The ruler failed to follow the principle of attacking while the enemy is only halfway across, and so was defeated.

Another example comes from Wu’s campaign against Chu. The Chu army retreated to Qingfa and was about to be pursued when King Fuga of Wu said, “Even a trapped animal will fight to the death—how much more so a person? If they know they must die and fight desperately, they will wear us down. But if those who cross first believe they can survive, and those still behind envy their escape, no one will be willing to fight to the death. Wait until they are halfway across, then attack, and we can win.” The Wu army followed his advice and won again.

When the Wei general Guo Huai was in Hanzhong, Liu Bei planned to cross the Han River and attack. The other generals proposed lining up along the river to resist him. Guo Huai said, “That would make us look weak and would not blunt the enemy’s advance. It is a poor plan. Better to form our ranks farther from the river, draw the enemy across, and attack when half the force has crossed. Then Liu Bei can be defeated.” Once the formation was in place, Liu Bei grew wary and did not dare to cross.

During the Wude era of the Tang dynasty, Xue Wanjun and Luo Yi were defending Youyan when Dou Jiande led a force of one hundred thousand to attack Fanyang. Wanjun told Luo Yi, “We are outnumbered. If we fight head-on, we will certainly lose; we must use a stratagem. Have weak soldiers and inferior horses form a line behind the city, blocking the river and luring the enemy. When the bandits cross to attack, lead a hundred picked cavalrymen and lie in ambush beside the city. Then strike when they are halfway across.” They followed this plan, and Wanjun defeated Jiande as his army crossed the river.

Zhang Yu sums up the principle: when an enemy brings its army across a river to fight, do not meet it at the water’s edge. Wait until it is halfway across, its ranks are not yet in order, and its front and rear cannot support each other; then attack, and victory is certain. Gongsun Zan’s defeat of the Yellow Turbans at Dongguang and Xue Wanjun’s defeat of Dou Jiande at Fanyang both used this method.

An army that intends to initiate battle should not position itself right by the water to “meet” the enemy—that is, waiting for them to cross and then attacking.

The commentators broadly agree, though they use different terms for the opposing sides. Cao Cao says that fu means to draw near. Li Quan says that if you meet the enemy beside the water, they will often dare not cross, leaving you unable to force them onto the bank for a decisive battle. Du Mu says: if you want to fight but meet the enemy by the water, they will suspect that you dare not cross and may refuse to engage. Du You, Mei Yaochen, and others likewise stress that when seeking a decisive battle, it is often better to stay some distance from the water and lure the enemy across before attacking. Zhang Yu sums it up: if I am determined to fight, I should not meet the enemy near the water, lest they stay on the far bank; if I do not want to fight, I can use the water as a barrier and prevent them from crossing. The Jin general Yang Chufu and the Chu general Zi Shang confronted each other across the Zhi River. Both armies withdrew in turn, each hoping the other would cross first so that its own troops could wait in comfort. In the end, neither side fought, and both went home. This is a classic example of “meeting the enemy by the water” and “luring them across.”

“Choose life and occupy high ground”

Cao Cao: Even when encamped beside water, occupy high ground; have water in front and high ground behind. Mei Yaochen: Beside water, too, one should occupy high ground and face the sun. Wang Xi considers that Cao Cao’s phrase “beside water, one should also occupy high ground” may not mean staying close to the water, and suspects that lines such as “for fear of being flooded” may have been placed incorrectly in the commentary. He Yan: “Choose life” means face the sun and keep a broad view; “the army occupies high ground” makes it easier to observe the enemy and harder to be caught in a surprise attack. Zhang Yu: Whether deploying on the bank or on boats, one should face the sun and occupy high ground, making it easier to observe the enemy’s position.

“Do not face the current”

(Read together with the preceding line, the main idea is:) Do not camp or form ranks facing the current. Moving downstream with the water’s force is disadvantageous and makes the army more vulnerable to flooding and surprise attack. In keeping with “choose life and occupy high ground,” deploy on a high bank, facing the sun and with dangerous terrain behind.

This passage explains how different commentators interpret the instruction in The Art of War not to approach water or camp in low-lying ground. Its central point is simple: near water, your forces should occupy high ground and the upstream position. Do not camp downstream or in a hollow, where the enemy could flood your camp by releasing water, attack with the current, or poison the water upstream and let it flow toward you.

Cao Cao and Li Quan both say the danger is that the enemy might dig channels or break a dam to flood the camp. They cite the example of Zhibo of Jin flooding Zhao Xiangzi.

Du Mu gives a fuller explanation. Since water flows to low ground, you must not station troops in a hollow near the water: if the enemy breaks a dike, the whole army could be flooded. This is the same principle as Sun Wu’s advice to identify ground where one can survive and occupy high places. Du Mu also gives two examples: Zhibo flooding Zhao Xiangzi, and Emperor Guangwu (Liu Xiu), who faced Wang Xun by using the force of water flowing down from higher ground and defeated him.

In his discussion of naval warfare, Zhuge Liang (the Marquis of Wu) says not to form up on the water against the current. Your own fleet should not anchor downstream, either; the enemy can come downriver and close in to attack with ease.

Jia Lin says that in a place with abundant water, the enemy can flood you and can also release poison upstream to drift down with the current. “Facing” here means going against the current. Some commentators also say that camping against the current is forbidden by military practice.

Mei Yaochen says not to station troops downstream, for fear of being flooded if the enemy breaks a dike. Fighting from boats against the current is also disadvantageous.

Wang Xi says that one should occupy the upstream position.

During the Three Kingdoms period, Cao Ren of Wei planned to attack Ruxu Islet, then held by Eastern Wu, and wanted to enter the islet and set up camp. Jiang Ji warned him that the enemy held the western bank and had its fleet arranged upstream. If their own army entered the islet to camp, it would be walking into a dead end and would surely be defeated. Cao Ren ignored the warning and was indeed defeated.

He Shi says that attacking the enemy while moving downstream takes less effort and offers an advantage.

Zhang Yu brings these points together: do not camp in low ground, where the enemy could flood your camp; and in naval warfare, do not remain downstream, where it is difficult to attack the enemy against the current and where you must also fear poison drifting down from upstream. When the Prime Minister of Chu faced Wu, an oracle said that battle would bring bad luck. Sima Ziyu replied: “Our army can occupy the upstream position—why would it be unlucky?” They went into battle and won. A naval force, therefore, should especially make sure to occupy the upstream position.

Throughout, the passage warns of the dangers of camping near water. Low ground exposes you to flooding; a downstream position exposes you to attacks carried by the current and to poisoned water. If you can occupy the upstream position, do so.

A Plain-Language Explanation

Mei Yaochen says: When an army fights on water, it must keep in mind the five principles discussed earlier. Zhang Yu says: Any army arrayed near the water counts as an “army on water.” When engaging the enemy on water, it should take those five principles as its rule.

When crossing saline marshland, pass through as quickly as possible; do not stop there.

Chen Hao says: “Salt marsh” means land made salty by brine, where the water and vegetation are poor and the ground gradually becomes waterlogged and sandy. It is unsuitable for stationing troops. The New Commentary says: This refers to land that is naturally saline and marshy, where no grain will grow. Jia Lin says: Saline land is often short of both water and vegetation, so an army cannot stay there long. Mei Yaochen says: “Salt marsh” also suggests open, far-reaching terrain. It is exposed and difficult to defend, so an army should not stay long. Wang Xi says: “Salt marsh” means saline land: broad, low-lying terrain with no defensible position to rely on. Zhang Yu says: The Treatise on Punishments and Laws uses the phrase “mountains and rivers, deep waters and salt marshes.” Yan Shigu’s commentary explains that “deep waters” means places beneath deep water, while “salt marsh” means saline land. Thus, salt marshes are barren, brackish, waterlogged places. The ground is damp, and the water and vegetation are poor, so an army should cross them quickly.

If you have no choice but to fight the enemy in a salt marsh, keep near water and vegetation, with dense woods behind you.

Cao Cao says: This means that you have no choice but to meet the enemy in a salt marsh. Li Quan says: If there is no time to get away and you must fight, take up position by the water. But because the water and vegetation are poor, you should still leave the area as quickly as possible.

When forced to meet the enemy in salt marshes

Cao Cao says: When there is no other choice, engage the enemy in salt marshland.

Li Quan says: If there is no time to pass through quickly, you must fight there. In battle, stay close to water and keep trees at your back. With water and trees nearby, the ground is less likely to swallow men and horses.

Du Mu says: Plants struggle to grow in saline soil. The ancients called such terrain “Flying Blades.” If you suddenly encounter the enemy there, choose a place with water, grass, and trees to set up camp and halt.

Du You says: Some editions read “with dense trees at your back.” The point is that if you meet the enemy in salt marshland, you should hold your ground with a dense forest behind you. This uses the advantages of the terrain to strengthen your forces.

Mei Yaochen says: When you meet the enemy in salt marshland, keep two principles in mind: stay close to water and grass, and keep trees at your back.

Zhang Yu says: When deploying troops in salt marshland, follow these two principles.

“This refers to troops in salt marshland”—that is, how to camp and arrange your formations there.

Easy ground on open plains

Cao Cao says: Flat land makes it easy for chariots and cavalry to gallop.

Du Mu says: On open plains, position your troops on ground that is flat and secure, so chariots and cavalry can charge and pursue the enemy.

Wang Xi and Master He offer views close to those of Cao Cao or Du Mu.

Zhang Yu says: Open plains are where chariots and cavalry can put their strength to use. Choose ground that is flat and free of pits and hollows for your camp; this makes it easier to break through enemy lines.

With high ground on the right and behind, and open ground in front

The army should have high ground to its right and rear. The front should allow it to engage in battle, while the rear should leave room to maneuver—that is, the front may be dangerous, but the rear should offer a way out. This is a common principle for establishing camp on level ground.

Commentaries on The Art of War: Terrain and the “Four Armies”

Cao Cao says: “Warfare is about arranging matters so that one can act to advantage.”

Li Quan says: “People handle tools most easily with the right hand, so an army should have that side at its back. ‘Death in front’ means that enemy territory lies ahead, making retreat difficult. ‘Life behind’ means that one’s own side is behind, where one can hold ground or withdraw.”

Du Mu says: “The Methods of War of the Grand Duke states that when marching, one should keep rivers and marshes to the left and hills to the right. ‘Death’ refers to low-lying ground; ‘life’ refers to elevated ground. Low ground cannot hold back high ground, and cavalry needs room to charge in battle, so one should have high ground at one’s back. The enemy’s ‘deadly’ territory lies ahead, while one’s own place of safety lies behind.” The same point is repeated below.

Jia Lin says: “Ridges and high ground are called ‘life’; ground suited for battle is called ‘death.’ With ridges and high ground behind, the army is secure; with the battlefield ahead, troops can be deployed conveniently. With high ground to one’s right, turning and maneuvering are easier.”

Mei Yaochen says: “Choose level, passable ground so that chariots and cavalry can move effectively. With hills behind to the right, the terrain offers support. Lower ground ahead and higher ground behind favor combat.”

Wang Xi says: “An army should face the sun and have a mountain at its back. If so, it would have ‘life in front and death behind,’ the opposite of what the other commentators say. He suspects the original text is mistaken.”

Zhang Yu says: “Even on level ground, there must be high ground. The army should have high ground behind it on the right, so it can use the terrain to its advantage. Lower ground ahead and higher ground behind make it easier to charge and pursue.”

“This describes deploying an army on level ground”—that is, how to array troops on level terrain.

Mei Yaochen says: “When camping on level ground, one should understand the two points given above.”

Zhang Yu says: “In battle on level ground, follow the principles of making it easy to charge and having high ground behind to the right.”

“The advantages of these four kinds of terrain for an army”

Li Quan says: “The four kinds of terrain are mountains, water, saline marshes, and level ground.”

Zhang Yu says: “This refers to the principles for deploying troops in four types of terrain: mountains, water, saline marshes, and level ground.”

Zhuge Liang (quoted): “In mountain warfare, do not force your way up to high ground. In water warfare, do not press against the current. In grassland warfare, do not venture recklessly into the depths. On level ground, do not attack a position that is empty and unsupported. These are the advantages of employing troops.”

Some commentators explain that understanding the advantages of these four kinds of terrain was one of the foundations on which the ancients won through their use of the land. Statements such as “the reason the Yellow Emperor defeated the Four Emperors” emphasize adapting one’s methods to the terrain, rather than merely recounting a myth.

Commentaries on “the Yellow Emperor … overcame the Four Emperors”

Cao Cao says: When the Yellow Emperor first rose to power, the lords of the four quarters all claimed the title of emperor. The Yellow Emperor prevailed over them by winning in all four kinds of terrain. Li Quan says: The Yellow Emperor learned the art of war from Feng Hou and pacified the four quarters; hence the claim that he overcame the “Four Emperors.” Mei Yaochen says: Perhaps “Four Emperors” is a mistaken writing of “Four Armies”? The meaning would be that the Yellow Emperor gained the advantage of four kinds of terrain: in the mountains he defeated those on mountain terrain, on the water he defeated those on the water, in marshes he defeated those in marshes, and on level ground he defeated those on level ground. Wang Xi says: Some texts write “Four Armies” instead of “Four Emperors.” Cao Cao says: When the Yellow Emperor first took power, the lords of the four quarters all claimed the title of emperor, and he prevailed by making use of four kinds of terrain. Some editions omit the character zuo and instead have yi. He’s comment says: Mei’s interpretation is persuasive. Zhang Yu says: When the Yellow Emperor first took power, the lords of the four quarters also claimed the title of emperor, and he prevailed by making use of four kinds of terrain. According to the “Basic Annals of the Yellow Emperor” in the Records of the Grand Historian, he fought the Flame Emperor at Banquan, fought Chiyou at Zhuolu, and drove the Xunyu north. The Six Secret Teachings of Taigong also says that the Yellow Emperor fought seventy battles before bringing the realm to order. This shows that he did indeed wage war against the lords of the four quarters. Since the art of war began with the Yellow Emperor, the text puts it this way.

The text: In general, an army prefers high ground and avoids low ground,

Mei Yaochen says: High ground is dry and open, making it suitable for encampment and allowing room to deploy one’s forces. Low ground is damp and unhealthy, and is also unfavorable for battle. Wang Xi says: Choose a position that is easy to descend from rather than climb to, and keep clear of floods. Zhang Yu says: From high ground one can observe easily and move freely; low ground is hard to defend and prone to illness.

values the sunny and disdains the shaded,

Mei Yaochen says: Sunny ground is bright and agreeable, while shaded ground is dark and unfavorable. Wang Xi says: Remaining for a long time in a damp, shaded place can cause distress and illness, and can also damage weapons. Zhang Yu says: The southeast is associated with Yang, and the northwest with Yin.

nurtures life and occupies solid ground;

(When choosing a camp, favor a place that supports the troops’ health and provides firm, dependable ground: near hills and woods, dry and facing the sun, with a stable foundation. Avoid low-lying, damp, unstable places. These are the same principles as “prefers high ground and avoids low ground” and “values the sunny and disdains the shaded.”)

Plain-Language Commentary on The Art of War

Cao Cao says: “Fullness” means having ample troops and provisions. “Preserving life” means keeping the army near places rich in water and pasture, where it can graze animals and raise horses and pack beasts. “Secure ground” also means high, firm terrain. (Note: The final name in the original is “Mei Yaoyin,” likely an error for “Mei Yaochen.”)

“Preserve life and occupy secure ground.”

Cao Cao: Rely on a state of fullness and abundance. To preserve life is to move toward places with water and pasture, where one can graze animals, raise livestock, and prepare warhorses. Secure ground is like occupying high terrain.

Mei Yaochen: Preserving life means having easy access to water and pasture; occupying secure ground means keeping supply routes open.

Wang Xi: Preserving life means having ample provisions, including water, pasture, and food. Occupying secure ground means relying on terrain that is firm and advantageous.

Zhang Yu: Preserving life means grazing and resting in places with good water and pasture; occupying secure ground means making camp on elevated land.

“An army free from a hundred ailments is certain to win.”

Li Quan: People who stay for a long time in low, damp places are prone to illness. Only high, sunny ground is suitable for a long stay.

Du Mu: Life belongs to Yang, and secure ground is high ground. By preserving life on high ground, one avoids low, damp, shaded places, where a hundred illnesses arise. Only then can victory be called certain.

Mei Yaochen: If the three things above are done well, victory can be assured. Epidemics will not break out, and the army will remain strong.

Zhang Yu: By staying on high, sunny ground and preserving life in a substantial setting, victory can be assured. The terrain is dry, so epidemics and illnesses are less likely to occur.

“In hills and along embankments, always take the sunny side, with the right flank and rear protected by the terrain.”

Du Mu: In areas of hills and embankments, the army should generally stay on the southeastern side, facing the sun and sheltered from danger.

Mei Yaochen: One need not be at the very highest point, but should face bright, sunny ground, with firm, elevated land protecting the right flank.

Wang Xi: On the sunny side, people feel at ease and move freely, and weapons are easier to maintain and use.

Zhang Yu: Facing the sun makes observation easier and commands clearer; having high ground behind provides protection and a defensible position.

“These are the advantages of warfare, aided by the terrain.”

Mei Yaochen: The advantage in warfare lies in gaining the terrain’s strength as support.

Zhang Yu: The advantage in warfare lies in receiving the help of favorable terrain.

“When heavy rain falls upstream and the floodwaters rush down foaming, anyone intending to ford the river should wait until the waters settle.”

When heavy rain falls upstream, floodwaters carrying foam surge down. Anyone planning to cross the river on foot should wait until the current calms and the water level becomes stable.

Cao Cao says: “The danger is that the army may reach the middle of the river when the water suddenly surges.” Li Quan says: “The fear is that the river will rise sharply.” Du Mu says: “When crossing a river, if you see foam on the water upstream, it means that it is raining farther up the river. Wait until the foam has dispersed and the current has settled before crossing. Otherwise, a sudden flood may rush down while you are halfway across, putting you in danger.” Du You also says: “The fear is that the water will suddenly rise when you are halfway across.” In principle, river water should clear after rain. If instead it turns muddy and foam rushes downstream, the enemy may have deliberately held back the water, intending to trap your army in midstream and cut it in two. Whenever a flood is coming, foam often arrives first. This is a danger that can destroy an army; wait until the water has settled before acting. Mei Yaochen says: “If the foam has not dispersed, a sudden rise in the water may be feared.” Wang Xi says: “Foam appears when the water rises; ‘wading’ means crossing on foot. Cao Cao’s explanation is correct.” Zhang Yu says: “Before the crossing is complete, a great flood suddenly arrives.” “Foam” refers to bubbles on the surface of the water.

Whenever you encounter any of the following six kinds of perilous terrain, leave as quickly as possible and do not approach:

Impassable ravines: steep, dangerous slopes on both sides, with a stream running through them.

Heavenly wells: low-lying places where water gathers, surrounded by high ground.

Heavenly prisons: enclosed by steep barriers on three sides, easy to enter but difficult to leave.

Heavenly nets: dense vegetation that makes it difficult to wield weapons.

Heavenly pits: low-lying, muddy terrain that is difficult for chariots and cavalry to cross.

Heavenly clefts: narrow, treacherous passages between two facing mountains.

The explanations of these six harmful kinds of terrain are mostly based on Mei Yaochen’s commentary.

This passage discusses the “six perilous types of terrain” in The Art of War. When an army passes through or camps, it should avoid them as far as possible. It must not approach them, much less fight with them at its back.

Cao Cao’s summary is as follows: a place with deep mountains and broad waters is called a “Severed Gorge”; a place higher in the middle and lower all around, like a basin, is called a “Heavenly Well”; a passage in the deep mountains that seems enclosed like a cage is called a “Heavenly Prison”; terrain that can trap people like a net, making escape difficult, is called a “Heavenly Net”; sunken, muddy ground that ensnares the feet is called a “Heavenly Pit”; and a narrow mountain ravine, with a channel several feet deep and several dozen feet long, is called a “Heavenly Crevice.”

Du Mu, citing military texts, says: a low-lying place where large volumes of water collect is a Heavenly Well; a narrow ravine that blocks passage is a Heavenly Prison; a ravine with deep, murky water of uncertain depth, where the muddy path is difficult for people and horses to cross, is a Heavenly Pit; a place full of gullies and pits, with hollows among rocks and trees, is a Heavenly Crevice; and a place concealed by trees and dense reeds is a Heavenly Net.

Jia Lin distinguishes the types in greater detail: a deep, wide gorge between two banks that blocks passage is a Severed Gorge; a low basin is a Heavenly Well; a place surrounded by dangerous ravines, with water and vegetation, sloping toward the center and difficult to enter or leave, is a Heavenly Prison; a rough path of irregular width, narrow and slippery underfoot, is a Heavenly Net; land that is mostly waterlogged and muddy is a Heavenly Womb; and a narrow, several-mile-long passage hemmed in by extremely dangerous slopes, impassable in the middle and easy to seal off at both ends, is a Heavenly Crevice. He also stresses that these six dangerous types of terrain must not be approached or left at one’s back. Mei Yaochen likewise says that even approaching such terrain is forbidden—how much more so is camping there?

Wang Xi believes that “Severed Gorge” in the original text may have been “Severed Heavenly Gorge,” with the word “Heavenly” omitted. He explains that these are all natural features: “prison” resembles a jail, “net” resembles a snare, “pit” refers to gullies, hollows, and mud, and “crevice” refers to places among rocks and trees. An army must not pass too close to them, or it may be caught off guard and unable to make use of either strategy or force.

Zhang Yu offers another summary: a deep, steep stream valley that cannot be crossed is a Severed Gorge; a place higher on the outside and lower within, where waters converge, is a Heavenly Well; a place ringed by dangerous mountains with a narrow entrance is a Heavenly Prison; a place concealed by crisscrossing trees and reeds is a Heavenly Net; a marshy, muddy place where carts sink and horses become stuck is a Heavenly Pit; and a narrow path full of hollows and depressions is a Heavenly Crevice. When an army encounters such terrain, it should take a wide detour and keep well away.

The overall meaning is consistent: the Severed Gorge, Heavenly Well, Heavenly Prison, Heavenly Net, Heavenly Pit, Heavenly Crevice, and related terrain such as Jia Lin’s Heavenly Womb are all grave hazards in warfare. They should be avoided at a distance; an army must not approach them, leave them at its back, or linger there.

When deploying troops, deliberately keep your forces at a distance from the six harmful kinds of terrain, while drawing the enemy close and making them turn their backs to these dangerous places. Our forces move toward advantageous ground, while the enemy is forced to face away from it. In this way, we can advance or withdraw freely and hold every advantage, while the enemy’s movements are impeded at every turn.

Cao Cao says that an army should always keep away from the six kinds of harmful terrain. If the enemy is drawn close and made to rely on dangerous ground, our position is favorable and theirs perilous. Li Quan says that a skilled commander leads the enemy into terrain that will work against them. Du Mu explains the words “face” and “back”: “face” means to look toward or move toward; “back” means to have one’s back against or rely on. When facing terrain of the six harmful kinds, our forces keep away from it and turn toward safer ground, leaving them free to advance or withdraw. The enemy, forced to approach and rely on dangerous ground, finds their movements obstructed; thus we benefit while they are endangered. Mei Yaochen and Zhang Yu make the same point: our forces keep away from the six harmful kinds of terrain and face toward safer ground, while the enemy draws near and relies on the dangerous terrain. Our movements and halts are advantageous; their advances and withdrawals are perilous.

Scouting on the March

When the army passes through difficult terrain, waterlogged hollows and pits, reed marshes, mountain forests, or dense undergrowth—places where ambush troops can easily hide—it must search carefully and repeatedly. Such places are often where spies and ambush forces lie in wait.

Cao Cao says: “Perilous ground” is terrain that rises high on one side and falls low on the other; “obstructed ground” is an area with abundant water. “Pools” refers to ponds, while “wells” refers to low-lying places. “Reeds” are places where grasses grow in dense clumps, and “mountain forests” are places thick with trees. “Shaded thickets” refers to places that provide cover and concealment. (This passage discusses terrain.) What follows concerns assessing the enemy’s situation.

Li Quan says: These points warn that the enemy may deploy surprise forces, set ambushes, or use deception to lure our troops into a trap.

Mei Yaochen says: Perilous and obstructed ground consists of narrow, strategic passes amid mountains and forests. Pools and wells lie in low places, where reeds grow; all of these can easily block visibility. They should be searched carefully to guard against ambushes.

Zhang Yu says: Perilous and obstructed ground is often found in hilly highlands, where mountain forests grow. Pools and wells lie in low places, where reeds abound; all can provide concealment. Search them thoroughly in separate groups, for fear that the enemy may be lying in wait. You must also guard against spies slipping in to observe our strengths and weaknesses and listen to our orders. “Ambushes” and “spies” should be treated as two distinct threats.

When the enemy is nearby but remains quiet, Mei Yaochen says: They do not move because they rely on the terrain’s natural defenses. Wang Xi says: They have defensible ground to rely on, so they are unafraid.

When the enemy is far away but comes to challenge us, it intends to lure our troops forward.

Du Mu says: (When discussing “the enemy nearby” and “challenging us from afar,”) if these are considered together with “spies and ambushes close at hand,” they should be distinguished as two separate situations.

Plain-Language Interpretation of Related Passages in Annotations to Sunzi

How can an enemy “challenge you from nearby”?

Du Mu says: If the enemy is close by and challenges you to fight, the two sides are often already very near one another. The enemy fears you may not dare advance, so he deliberately acts as if he is ready to fight, though he may have no intention of engaging at once.

Chen Hao says: If the enemy is nearby but does not challenge you, it is usually because he is relying on difficult terrain that he can hold while waiting for you to make the first move.

If the enemy is far away but challenges you repeatedly, he is probably trying to lure you forward. Once you have left your advantageous position, he can strike hard while the opportunity is in his favor.

Mei Yaochen and Chen Hao hold similar views. Wang Xi says the enemy’s aim is to make you act according to his timing. Here, “challenge” means to provoke or lure, drawing a bold enemy out to seek battle.

Zhang Yu says: If the two armies are close but remain still for a long time, they are relying on secure, difficult terrain. If they are far apart but the enemy challenges you again and again, he is trying to lure you forward.

The Wei Liaozi also says that if the enemy has taken up a difficult position, you should not force a battle with him. It further says that an enemy who challenges from a distance is often not at full strength. A distant challenge is usually meant to delay you or lure you deeper in, so you should not rush in with all your force. This accords with the reasoning here.

“Where he is stationed is easy and advantageous”

Cao Cao says: The place where the enemy is stationed is advantageous to him.

Li Quan says: Flat, easily traveled ground is favorable for marching and maneuvering; this is what “advantageous” means in military affairs.

Du Mu says: If the enemy does not wait in a difficult position but stays on flat ground, it must be convenient for carrying out his plans, such as supplying his troops or moving them about.

One version reads: “The soldiers compete for the places where they are stationed because they are easy and advantageous.” The troops all compete to occupy good ground because it is accessible and favorable.

Chen Hao says: Once the enemy has gained the advantage of the terrain, his subordinates will compete to occupy it.

Jia Lin says: If the enemy is stationed somewhere especially convenient, he may challenge you in order to lure you out to a position that favors him. In a battle, he can then gain the advantage easily. Do not fall for this lightly.

Mei Yaochen says: The enemy challenges you because his position is accessible and favorable. Wang Xi agrees with Cao Cao’s explanation.

Zhang Yu says: If the enemy leaves difficult ground and occupies an accessible position, he must have some purpose. Another explanation is that he deliberately waits on easy ground and displays an advantage to lure you forward.

“When many trees are moving, the enemy is coming”

If a large area of trees is shaking, the enemy army is probably passing through; the movement of people and horses has disturbed the trees. In ancient reconnaissance, this was a common sign that an enemy force was approaching. The original passage gives only the opening phrase, so its meaning can be explained from the words themselves.

This passage explains how, on the battlefield, to infer the enemy’s movements and see through their disguises by observing unusual activity among trees, plants, birds, and animals.

Trees swaying: Cao Cao, Zhang Yu, and others advise sending sharp-eyed observers to a high vantage point. If a stretch of forest sways when there is no wind, the enemy is probably cutting trees to clear a path or felling timber to make equipment or weapons. (One historical example is the Jin practice of cutting trees to reinforce their troops.) This is a sign that someone is deliberately making a disturbance.

Many obstacles in the grass: Sometimes the enemy has not yet finished building their camp, or is withdrawing quietly. To avoid pursuit or a surprise attack, they may put up woven grass screens or fake barriers along the road or in the grass, making it seem as though people are concealed there. Du Mu, Jia Lin, Du You, and Zhang Yu all stress that numerous screens often indicate a feint: they may hold you back by making you afraid to advance, or cover an attack from another direction. The enemy may also set up many barriers while pursuing you, making you suspect an ambush and slow down. In short, many barriers do not prove that anyone is there. Beware of attempts to divide your forces, make you hesitate, or lead you in the wrong direction.

Birds suddenly taking flight: Birds usually fly low. If they suddenly rise high from a particular place, Cao Cao, Li Quan, Du You, and Zhang Yu agree that troops are often concealed below, having startled them.

Wild animals fleeing in alarm: If animals suddenly scatter and rush away, it often means the enemy is about to attack or envelop you. The term fu here means to launch a surprise attack or press forward. This is a sign that the enemy is on the move.

Taken together, the key to observing the enemy in the tradition of Sunzi is to watch not only people and horses, but also trees, grass, birds, and animals. Unusual movement or stillness often conceals an ambush, a feint, or the enemy’s true intentions as they advance or withdraw.

On “Covering” (Surprise Attacks from the Flank or Rear)

Cao Cao says: When the enemy makes a great show of force and spreads out both wings, they are coming to encircle us from the flanks and rear. Li Quan says: An attack that comes unexpectedly and suddenly is called “covering.” Du Mu says: If the enemy means to launch a covering attack against us, they will most likely lie in ambush along another road, in a hazardous place, or in dense woods. Thus, if beasts are startled into flight and run about wildly, it means there are ambushers nearby. “Covering” means attacking from concealment. Chen Hao says: To cover is to hide among the trees and launch a quiet attack on our forces. Another possibility is that, while the two armies are locked in fierce battle, enemy troops suddenly appear to our left or right, or behind us, like beasts startled from hiding and scattering in panic. Mei Yaochen says: When beasts are startled and flee, there are often ambushers nearby. Zhang Yu says: Those who mean to launch a surprise attack usually emerge from hazardous terrain or from among the grasses and trees, startling hidden beasts and sending them fleeing in terror. “Covering” means coming to attack us.

Judging the Enemy’s Movements from Dust

Du Mu says: When chariots and horses move quickly, the troops often travel in single file, and the dust rises high and narrow. Du You says the same. Mei Yaochen says: Hooves and wheels press heavily against the ground, so the dust they raise must be high and sharply pointed. Zhang Yu says: When chariots and horses move both quickly and heavily, their tracks follow one after another, and the dust rises high in a pointed shape. Whenever an army marches, scouts must be sent ahead. As soon as they spot dust raised by the enemy, they must send word swiftly to the commander. This is like Pan Dang seeing dust rise from the Jin army and sending a messenger galloping to report it.

Low and Broad Dust Means Infantry

Du Mu says: Foot soldiers move slowly and can march side by side, so the dust is low and broad. Mei Yaochen says: People on foot move low and lightly, at an unhurried pace, so the dust must be low and broad. Wang Xi says: Chariots and horses raise dust with force, while infantry move much more slowly. Zhang Yu says: Foot soldiers advance slowly, their steps are light, and their formation is more spread out; therefore, the dust they raise is low and broad.

When dust is scattered and spread out in broken, intermittent streaks, the enemy is probably gathering firewood or cutting trees—or dragging branches to disguise the movement of troops. Li Quan cites historical examples: when Jin attacked Yu, its infantry moved slowly, left faint tracks, and marched in widely spaced formations, so the dust was low and sparse. When Jin attacked Qi, it dragged brushwood behind carts to raise dust. Seeing what looked like a large force from the mountain, the people of Qi fled by night. Dust raised by gathering wood or dragging brushwood tends to drift in different directions rather than rise in one thick column.

Du Mu says that when woodcutters go their separate ways, the dust spreads and fans out. “Streaked” describes lines running across and along the ground, broken here and there. Mei Yaochen says that when people gather wood in many places, the dust must spread sideways. Wang Xi explains that the streaks are fine, fragmented, and discontinuous. Zhang Yu says that when laborers are sent to cut wood in scattered places, the dust becomes disorderly, as though many small paths or tunnels had been traced across the ground.

When dust is slight and moves back and forth, the enemy is probably setting up camp. Du Mu says that troops preparing to build an encampment send light troops back and forth as scouts, so they raise little dust. Mei Yaochen says that light troops choose a camp site, and their movement produces only a little dust. Zhang Yu says that before setting up stockades and camps, the enemy often sends light cavalry to inspect the terrain nearby from all directions, assessing its hazards, accessibility, breadth, and narrowness. The dust is therefore faint and can be seen moving back and forth.

Plain-Language Interpretation

Cao Cao says: When an enemy envoy speaks humbly, and you secretly observe that the enemy is strengthening its camps and whitewashing its city walls, as if afraid of you, this is often a deliberate show of weakness meant to lull you into complacency before launching a sudden attack.

Du Mu gives an example: When Zhao She went to relieve Eyu, he set up camp thirty li from Handan and did nothing but build defenses, making no advance. The state of Qin sent a spy. Zhao She made sure the spy was treated well before being sent away. When the spy reported back to the Qin general, the general was delighted and said, “Eyu is already lost to Zhao.” But after sending the spy away, Zhao She marched quickly along a small road, caught the Qin army off guard, and defeated it.

Mei Yaochen says: Those who intend to attack present a humble front while tightening their defenses behind it. They are trying to deceive you and keep you waiting.

Zhang Yu says: The envoy speaks deferentially, while the enemy strengthens its defenses. Their aim is to make you arrogant first, then attack.

(Note: This passage repeats the section by Du Mu; the meaning is much the same.)

Tian Dan defends Jimo: The Yan general Qi Jie laid siege to the city. Tian Dan personally took up the tools for building defenses and worked alongside the soldiers. He had his wives and concubines make hemp ropes among the ranks, distributed food to reward the troops, and arranged for the women to appear on the city wall and agree to surrender. The Yan army was delighted. He also gathered a thousand yi of gold from the people and had wealthy residents send an envoy to the Yan general with a message: once the city surrendered, please do not plunder the wives and concubines. The Yan army grew even more complacent. Tian Dan then counterattacked and defeated it.

Another judgment from military strategy, set against the “humble words and increased defenses” described above:

When their words are forceful but their troops seem to be charging forward, they are often actually retreating—using a show of force to cover their withdrawal. Do not be fooled by the appearance of an advance.

Brief background notes

• Eyu: A place in the state of Zhao, contested by Qin and Zhao.
• Jimo: A city in the state of Qi. Tian Dan was a Qi general during the Warring States period, famous for tactics such as the fire ox formation. This passage concerns his feigned surrender and deception of the enemy.
• Jian (jiàn): A spy.
• Board-and-rammed-earth construction: Boards and rammed earth used to build city defenses; here, it refers to constructing fortifications.

Cao Cao says, “‘Deceit’ here means using trickery and false appearances to mislead the enemy.”

Du Mu gives an example. King Fuchai of Wu traveled north and met Duke Ding of Jin at Huangchi to conclude an alliance. Seizing the opportunity, King Goujian of Yue attacked Wu. Wu and Jin were vying over which state would take precedence, and the outcome was still uncertain. The king of Wu was worried and summoned his ministers to discuss whether it would be better to skip the meeting and return home, or to attend and claim precedence over Jin. Wangsun Luo said, “We must attend, and we must be first.” The king asked, “How can we be first?” Luo replied, “Tonight we must challenge the Jin army to raise the spirits of our soldiers and people. That way, we can take precedence at the alliance meeting.” The king of Wu then led thirty thousand armored troops and formed ranks one li from the Jin army, their imposing presence shaking heaven and earth. Jin sent Dong He to investigate. The king of Wu answered him in person: “I will serve your lord today—or I will not serve your lord today.” Dong He reported back, “From the king of Wu’s expression, I judge that he is deeply worried. The Wu army will fight desperately; we must not engage them.” Jin therefore agreed to let Wu perform the first blood oath, the alliance ceremony that signified leadership. After the meeting, the king of Wu led his troops home.

Du You says, “They act deceptively, displaying their movements and making a show of fearlessness, when in fact they know they are about to withdraw.” Mei Yaochen says, “A side that intends to withdraw often sends an envoy who speaks forcefully, while its army advances aggressively, in order to intimidate us.” Wang Xi says, “They speak forcefully and make a show of advancing so that we will not expect them to retreat.” Zhang Yu says, “The envoy speaks boldly while the army presses forward, intending to intimidate us and thereby ensure a smooth withdrawal.”

(The Art of War also says:) “When light chariots move out first and take up positions on the flanks of the main force, the army is forming its battle array.” Here, “array” means a military formation.

There is another example from warfare. Qin sent a man by night to tell the Jin army, “The soldiers of both armies have not yet had sufficient rest. Let us meet tomorrow.” Yu Pian of Jin said, “The envoy’s darting eyes and insolent speech show that they fear us.” Sure enough, Qin fled that very night.

A Plain-Language Interpretation of Sunzi’s Annotations

Cao Cao says: Deploying troops and making a show of readiness to fight is what is meant by “arraying troops as if about to engage.”

Du Mu explains: Light chariots are sent out first to mark the battle formation’s boundaries and establish its layout. Jia Lin says: When light chariots move ahead, it signals that the enemy is approaching to form up for battle. Zhang Yu says: “Light chariots” means war chariots. Deploying troops beside the chariots while soldiers sing and shout is a show of force and readiness to fight. In the “Fish-Scale Formation”—a formation arranged in successive overlapping ranks like fish scales—the flanking units come first, followed by the ranks of foot soldiers. In other words, the chariots charge ahead and the infantry follows behind. So when an army is “about to engage,” its chariots often appear first on the flanks.

“When someone seeks peace on their own, without any prior agreement, it is usually a plot.”

Li Quan says: If someone comes to negotiate peace without an oath or guarantee, they must be scheming against the other side. Examples include Tian Dan’s ruse to deceive Qi Jie during the Warring States period and Xin Ji’s feigned surrender to Xiang Yu in the early Han. Both are instances of this kind.

Du Mu cites an event from the third year of the Zhenyuan era under Emperor Dezong of the Tang. The Tibetan leader Shang Jiezan had raided the area around the Hequ, then suffered an epidemic that killed more than half his men and horses. Fearing he would not be able to return, he put on a show of sincerity, proposed peace talks with Chancellor Ma Sui, and requested a formal meeting to make an oath. Ma Sui agreed. At the time, Hun Jian, military governor of Hezhong, submitted a memorial saying: “If the state has stationed troops on the frontier and is planning an attack, then the Tibetans’ request for an oath might be considered. But the Tibetans have no demands of the state and are urgently seeking a meeting. They probably have hostile intentions.” The emperor did not heed his warning. Hun Jian stationed twenty thousand troops in Pingliang County, Jingzhou. The oath-taking altar was thirty li west of the county. On the thirteenth day of the fifth month, Hun Jian brought three thousand men to the altar. As expected, the Tibetans arrived in armor and used the meeting to launch a raid. Chen Hao says: Using an oath-taking meeting as cover for an attack is not limited to the present dynasty. In the Spring and Autumn period, Jin and Chu met to make an alliance in the state of Song. The men of Chu wore armor, intending to attack Jin; the Jin side discovered their plan, and Chu lost its credibility. The phrase “seeking peace without prior agreement” is a general observation about how two states conduct war: whether the other side invades or seeks peace, beware of a peace offer made without prior agreement that is actually a deceitful plot.