《孫子註解》Vol. 13

The thirteenth volume of Commentaries on Sunzi discusses the critical importance of espionage. Both Cao Cao and Li Quan emphasize that warfare necessitates the use of spies to gather intelligence on the enemy. Zhang Yu adds that to obtain accurate information about the adversary, espionage is indispensable—but the methods must remain utterly clandestine, which is why this section follows immediately after the tactics of fire attacks.

Sunzi states that mobilizing an army of 100,000 troops to march a thousand li imposes a daily burden on the people and state coffers amounting to a thousand pieces of gold. The upheaval affects both domestic and foreign affairs, as civilians are forced into labor, disrupting agricultural work. The number of households impacted reaches as many as 700,000. Cao Cao explains that in ancient times, eight households formed a neighborhood (lin). If one household sent a soldier to war, the other seven were responsible for logistical support. Thus, deploying an army of 100,000 meant 700,000 households could no longer tend their fields.

Li Quan elaborates: in antiquity, conscripting one household for military service required the support of three allied clans, so 700,000 households were needed to sustain an army of 100,000. Du Mu illustrates this with the jingtian (well-field) system: in nine qing of land, the central qing was reserved for wells and dwellings, shared by eight families—hence the name "well-field." The 700,000 households, tasked with transporting supplies for the 100,000 troops, were exhausted from endless travel. Mei Yaochen agrees with Cao Cao, noting that the transport of provisions and equipment imposed heavy corvée duties on both state and private sectors, leaving the people unable to farm. Zhang Yu further clarifies that when fighting in critical enemy territory, armies must not only transport grain but also weapons and gear. The key to military success lies in seizing enemy resources, as deep incursions risk supply shortages and must rely on confiscation—not merely plundering enemy granaries, for some desolate regions have no food to take. How, then, can armies avoid transporting their own provisions?

If two sides remain locked in stalemate for years, striving for victory in a single day, yet begrudge noble titles, stipends, and wealth to obtain enemy intelligence, this is the height of inhumanity. Li Quan remarks that withholding rewards and refusing to employ spies for reconnaissance is the gravest form of cruelty. Du Mu interprets this as reluctance to invest heavily in espionage. Mei Yaochen observes that after years of standoff, the burden on 700,000 households is already immense—yet they hesitate to spend trivial sums on titles and money, a grave lack of wisdom.

This commentary discusses the crucial importance of intelligence work in warfare and the severe consequences of being stingy with rewards and failing to properly utilize spies.

Wang Xi and Zhang Yu criticize generals who begrudge material resources and are unwilling to offer substantial rewards to recruit spies, considering this extremely inhumane conduct. Protracted warfare causes massive expenditures (mentioning how seven hundred thousand households become financially strained), and when commanders still withhold noble titles and rewards, refusing to use material incentives to gain enemy intelligence through spies, this reaches the height of inhumanity.

The commentators highlight from different perspectives that such generals are unfit to lead armies (Mei Yaochen states "this is not a commander capable of leading troops to victory"), unqualified as state advisors (another version says "those who don't assist the nation with virtue"), and certainly cannot become architects of victory. Zhang Yu concludes: such individuals can neither command troops nor assist their sovereign, much less determine victory. The commentators repeatedly emphasize these points to express profound regret.

Truly enlightened rulers and capable generals achieve certain victory and extraordinary accomplishments precisely because they obtain enemy intelligence beforehand. Commentators like Li Quan and Du Mu all stress the importance of spy work. Mei Yaochen points out: wise rulers never act rashly - when they move, victory is assured; excellent generals never recklessly pursue merit - when they achieve, their accomplishments stand out. All this stems from prior knowledge of enemy situations. Wang Xi adds that foreknowledge enables one to prevail with divine efficacy.

He Shi cites the Rites of Zhou to show how specialized intelligence officers existed since antiquity (the Shi Shi official managed state espionage), then provides two historical cases: Northern Zhou's Wei Xiaokuan excelled at using spies, even making Qi state operatives secretly transmit intelligence for him; Western Wei's Li Da generously treated border residents as spies, continuing espionage operations even when informants were executed for leaks. These cases demonstrate how outstanding commanders all valued intelligence work, using spies to anticipate enemy movements beforehand.

(Note: The term "jian" refers to spies; "Yubi" was a key Northern Zhou military stronghold; "Wei Xiaokuan" and "Li Da" were both renowned generals of the Northern and Southern Dynasties period.)

Zhang Yu explains that one must first understand the enemy's situation before taking action to secure victory, achieving accomplishments far surpassing ordinary people. This "foreknowledge" cannot be obtained by appealing to ghosts or deities, as spirits are formless and cannot provide intelligence through sacrifices or prayers.

Both Cao Cao and Li Quan emphasize that intelligence cannot be gained through sacrificial rituals or by drawing analogies from similar events. Du Mu points out that "analogy" (象) refers to comparisons—one cannot infer the enemy's situation from unrelated matters. Mei Yaochen adds that neither divination nor analogical reasoning can reveal the truth. Zhang Yu concludes that intelligence cannot be acquired by comparing unrelated phenomena.

Regarding the idea that "it cannot be verified by measurement" (不可验于度), Cao Cao states that conventional calculations are unreliable. Li Quan explains that "measurement" (度) refers to quantification—while physical distances can be measured, the true intentions of people cannot be gauged by any standard. Mei Yaochen argues that numerical verification is impossible, illustrating the difficulty of anticipating the enemy's moves. Zhang Yu notes that intelligence cannot be deduced through statistical projections.

Obtaining enemy intelligence ultimately depends on human effort. Cao Cao stresses the necessity of relying on human agents. Li Quan specifically highlights the use of spies. Mei Yaochen analyzes: while supernatural matters may be approached through divination, natural phenomena through analogy, and cosmic patterns through numerical verification, enemy intelligence can only be obtained through espionage. Zhang Yu summarizes: neither divine consultation, analogical reasoning, nor mathematical calculation can provide foreknowledge—only human intelligence can reveal the truth.

There are five types of spies: local spies (因间, utilizing natives), inside spies (内间, bribing enemy officials), double agents (反间, turning enemy spies), expendable spies (死间, delivering false intelligence), and surviving spies (生间, those who return alive). Mei Yaochen identifies these as the five categories of espionage. Zhang Yu clarifies that "因间" should be read as "乡间"—spies recruited from local populations.

When all five types of spies are deployed simultaneously, the enemy becomes unable to discern their methods. This constitutes the mystical art of espionage—a ruler's ultimate weapon for victory. Cao Cao advocates employing all five categories concurrently. Li Quan suggests tailoring each method to specific targets. Du Mu explains that "activating all five spies" (五间俱起) means confounding the enemy's ability to distinguish truth from deception.

This passage discusses the mysteries and methods of "using spies" (espionage activities) in ancient military strategy.

The core idea is that the true mastery of espionage lies in ensuring the enemy remains completely unaware of how intelligence is obtained—this unfathomable technique represents the highest state secret in governing and military affairs. When all five types of spies (local spies, inside spies, double agents, expendable spies, and living spies) operate simultaneously, the enemy cannot possibly discern their workings. This is what is called the "divine web of strategy"—the ruler's most treasured key to victory.

Specifically explaining the method of "local spies": this involves using native individuals from the enemy state as intelligence sources. The Tang dynasty commentator Du Mu cites examples such as the Jin dynasty general Zu Ti, who, while garrisoned at Yongqiu, treated local civilians kindly, earning him secret informants even from enemy-controlled regions. Another example is the Western Wei general Wei Xiaokuan, who bribed Northern Qi subjects to assassinate enemy commanders. Other commentators add that during the Spring and Autumn period, when Chu attacked Song, the Song minister Hua Yuan infiltrated the Chu command tent at night to threaten their general, ultimately forcing Chu to retreat thirty li—another classic case of leveraging enemy personnel.

The key to employing "local spies" lies in understanding the enemy's weaknesses through their own people and incentivizing them with benefits to serve one's own cause. Just as Wei Xiaokuan used gold and valuables to bribe Qi subjects for intelligence, these spies do not require specialized training from one's own side. Instead, they are sourced in situ—exploiting the enemy's internal personnel—making them far more covert and effective.

This passage discusses the ancient military strategy of employing "internal spies" (neijian). These are enemy officials used as collaborators. Several scenarios are described: officials who possess talent but have been demoted, those punished for mistakes, the corrupt and licentious, unrecognized talents, opportunists seeking to prove themselves during turmoil, or those with wavering loyalties. All such individuals can be bribed with substantial wealth to gather intelligence and sow discord between rulers and ministers.

Du You further elaborates that officials who have suffered punishments—along with their families—can be exploited by capitalizing on their grievances against those in power. Mei Yaochen emphasizes establishing covert connections with enemy officials. He Shi provides historical examples: Li Xiong used a self-injury ruse by sending Pu Tai to feign surrender to Luo Shang, setting fires within the city as a diversion to crush the enemy; during the Sui dynasty, Yin Shou bribed Gao Baoning's confidant Zhao Shimu with riches, ultimately causing Gao's defeat and death; Tang Taizong employed similar tactics against Dou Jiande. These are classic cases of successful internal espionage.

(Note: "North of the Desert" refers to regions beyond the Gobi; "Mohe" denotes ancient ethnic groups in Northeast China; "Kaifu" was a high-ranking military office title.)

Dou Jiande led his troops to storm the Hulao Pass, inflicting heavy casualties as they pressed toward the enemy camp. His strategist Ling Jing proposed a plan: the entire army should cross the Yellow River, first seize Huaizhou and Heyang, and station elite forces there; then, with great fanfare, march across the Taihang Mountains into the Shangdang region. By first intimidating the enemy with overwhelming momentum, then issuing proclamations to demand surrender, they could gradually take control of the Hukou Pass, threaten the Pujin crossing, and ultimately reclaim the Hedong region—this was the optimal strategy. The plan offered three advantages: first, advancing into undefended territory ensured military success; second, it would expand territory and replenish troops; third, it would naturally lift the siege on Zheng (Wang Shichong's state). Just as Dou Jiande was about to adopt the plan, Wang Shichong’s envoy Zhangsun Anshi secretly bribed Dou’s generals with gold to disrupt the decision-making. The generals protested in unison: "Ling Jing is just a scholar—what does he know of warfare?" Dou Jiande ultimately yielded to their counsel, telling Ling Jing: "Our soldiers’ morale is soaring—this is heaven’s aid. Following their advice to engage in decisive battle will surely bring victory; I cannot accept your proposal." When Ling Jing persisted, Dou angrily rebuked and caned him. The result? The entire army was crushed in a reckless assault on Hulao Pass by Li Shimin’s forces. Dou Jiande, wounded by a spear, fled to Niukouzhu, where Tang generals Bai Shirang and Yang Wuwei captured him alive.

Another example occurred when the Qin general Wang Jian attacked Zhao. The Zhao state deployed its renowned commander Li Mu and Sima Shang to resist. Li Mu repeatedly defeated Qin forces, even slaying the Qin general Huan Yi. Wang Jian then bribed Zhao’s favored minister Guo Kai and others to spread rumors: "Li Mu and Sima Shang plan to ally with Qin, overthrow the King of Zhao, and secure fiefs for themselves in Qin." The King of Zhao fell for the ruse, replacing Li Mu with Zhao Cong and Yan Ju, executing Li Mu, and dismissing Sima Shang. Three months later, Wang Jian seized the opportunity to launch a ferocious assault, annihilating the Zhao army, killing Zhao Cong, and capturing King Qian of Zhao and Yan Ju.

(Zhang Yu’s commentary notes:) Exploit disgraced officials or persecuted descendants—anyone at odds with those in power—by luring them with substantial bribes. Historical precedents include Jin’s use of Xi Gong and Wu’s acceptance of Wu Zixu, both employing similar stratagems of sowing discord.

(Li Quan adds:) When the enemy sends spies to scout our weaknesses, lavish them with riches to turn them into double agents.

(Du Mu elaborates:) For enemy spies, either bribe them heavily to defect or feign ignorance, deliberately feeding them false intelligence before releasing them—thus turning their own spies into instruments of our advantage.

The passage recounts how Chen Ping (a founding strategist of the Western Han dynasty) devised a stratagem of sowing discord for Liu Bang, the King of Han, to fracture Xiang Yu's camp.

At the time, Xiang Yu had besieged Liu Bang in the city of Yingyang. When Liu Bang offered to cede lands west of Yingyang for peace, Xiang Yu refused. Chen Ping analyzed the situation: Xiang Yu had only a handful of truly capable advisors—Fan Zeng (honored as "Second Father"), Zhongli Mo, Long Ju, and Zhou Yin. He proposed using tens of thousands of catties of gold to execute a counterintelligence scheme, driving a wedge between the ruler and his trusted men.

Liu Bang approved the plan, granting Chen Ping 40,000 catties of gold to deploy freely. Chen Ping spread rumors among the Chu forces, claiming that generals like Zhongli Mo, despite their great merits, had not been enfeoffed as kings and thus sought to ally with Han to overthrow Xiang Yu and divide his lands. Xiang Yu, as expected, grew suspicious and sent envoys to the Han camp. Liu Bang deliberately arranged a lavish banquet to receive them, but upon seeing the Chu envoys, he feigned surprise, saying, "I thought these were envoys from Second Father!" He then replaced the feast with meager rations. When the envoys reported this, Xiang Yu’s distrust of Fan Zeng deepened.

Fan Zeng urged an immediate assault on Yingyang, but Xiang Yu ignored him. Upon realizing he was under suspicion, Fan Zeng, consumed by resentment, developed a fatal abscess on his back and died. Ultimately, Liu Bang employed Chen Ping’s stratagem to destroy the Chu state.

Later commentators added insights: The counterintelligence strategy could involve misleading the enemy with false information (as noted by Mei Yaochen) or tempting them with substantial bribes (as Wang Xi suggested). He Shi cited the example of Tian Dan during King Zhao of Yan’s reign, who used a similar ruse to make King Hui of Yan doubt his general Yue Yi, leading to a disastrous change in command. These cases illustrate that the essence of the stratagem lies in fostering internal suspicion among adversaries.

This passage recounts several classic cases of espionage and counterintelligence tactics employed in ancient warfare, presented here in modern language:

The first case occurred during the Warring States period when the Yan state attacked Qi. The Yan army desecrated the ancestral graves of Qi citizens outside the city walls, enraging the defenders of Jimo. Fueled by righteous anger, the Qi forces launched a fierce counterattack, crushing the Yan troops and recapturing over seventy lost cities.

Next is the story of Qin's siege against Zhao's Yanyu city. Zhao general Zhao She led reinforcements but deliberately halted his advance thirty li from the capital. When Qin spies came to investigate, Zhao She lavishly entertained them. The spies reported back that Zhao forces were cowardly, making the Qin commander lower his guard. Seizing this opportunity, Zhao She launched a surprise attack through forced march, decisively defeating the Qin army.

The most famous example is the counterintelligence plot at Changping. Qin chancellor Fan Ju dispatched agents to spread rumors in Zhao that their army particularly feared Zhao Kuo, while regarding Lian Po's forces as easily manageable. The Zhao king fell for this deception, replacing veteran general Lian Po with the bookish Zhao Kuo. Upon learning this, Qin secretly appointed their top general Bai Qi, who ultimately killed Zhao Kuo and executed four hundred thousand surrendered Zhao soldiers.

Zhang Yu's commentary notes: When discovering enemy spies, one should bribe them heavily to feed false information, or pretend unawareness while treating them coldly to let them carry back misleading intelligence. Zhao She's hospitality toward Qin spies and the Han army's feigned panic before Chu envoys exemplify such successful tactics.

Regarding "dead spies" (死间), these involve deliberately creating false scenarios known to one's own agents, who then transmit this misinformation to the enemy. Li Quan explains: When the enemy distrusts intelligence, we intentionally leak fabricated reports. Du Mu adds: Such spies often get executed when their false information contradicts reality - hence "dead" spies. For instance, after Han's Li Yiji convinced Qi to surrender, Han Xin's sudden attack led to Li being boiled alive by Qi's Tian Heng, illustrating this tactic.

Du You summarizes: First create false intelligence externally, deliberately let your own spies acquire it, then have them deliver it to the enemy. These cases demonstrate how intelligence warfare and psychological operations often proved decisive in ancient conflicts.

This passage discusses the ancient military tactic of "death agents" (spies sent on suicidal missions). When a spy infiltrates enemy territory and is captured, they must feed the enemy false intelligence. If the enemy believes this misinformation and strengthens their defenses accordingly, while our forces actually take the opposite action, the exposed spy will inevitably be executed.

Xiao Shicheng proposed a method: deliberately release certain prisoners or defecting soldiers after allowing them to "accidentally" overhear false intelligence before escaping back to enemy lines. The enemy often trusts such "coincidentally" obtained information, while the messengers bearing false reports ultimately meet their doom.

Several historical examples illustrate this: Duke Wu of Zheng feigned executing his minister who advocated attacking the Hu State to lull them into complacency; Ban Chao spread misinformation about troop shortages during his campaign against the Shache Kingdom, letting captives carry this news to the Qiuci king; Li Jing exploited Tang Jian's peace mission to the Turks as cover for a surprise attack. In each case, those who delivered the false intelligence were eventually executed by the enemy.

Zhang Yu further notes that sometimes warriors would be sent carrying forged documents into enemy camps, intentionally allowing their interception. Upon discovering the contents, enemies would typically execute both the couriers and their own strategists. For instance, Song Dynasty's Marshal Cao once had a condemned prisoner pose as a monk to deliver a wax-sealed secret message to Western Xia, causing their ruler to mistakenly execute his own ministers.

Ultimately, the essence of "death agents" lies in using human lives to transmit false intelligence, with both spies and messengers knowingly fulfilling their fatal missions. Like when Li Yiji served as envoy to Qi—while he negotiated peace for Liu Bang, the Han forces launched an attack, resulting in Li being boiled alive by the Qi king. Such ruthless stratagems reveal the treacherous and merciless nature of ancient warfare.

This passage explains the application of "living spies" (shengjian) in ancient warfare, where military strategists illustrate key principles of espionage through concrete examples:

Li Quan notes that a living spy refers to an agent capable of traveling between enemy and friendly forces to relay intelligence. Du Mu elaborates that such spies require exceptional qualities: an ordinary appearance masking sharp wit, seemingly mediocre abilities concealing true courage, endurance of harsh conditions, and even willingness to bear humiliation.

Jia Lin mentions that skilled spies must seamlessly blend overt actions with covert reconnaissance, shuttling intelligence undetected. Du You emphasizes selecting intelligent individuals who can ingratiate themselves with enemy leaders to observe their movements, discern weaknesses, and report back. Mei Yaochen illustrates this with examples like deploying eloquent speakers to gather intelligence.

He Shi cites classic cases: During the Spring and Autumn period, Hua Yuan infiltrated enemy camps to obtain critical information; in the Sui dynasty, Da Xiwu disguised himself as an enemy soldier, sneaking into their camp at night to gather intelligence that ultimately helped Emperor Taizu achieve decisive victory. Zhang Yu adds that spies might also spread disinformation—like the Qin state deliberately leaking false reports to mislead the Jin army, enabling a successful night attack, while Lü Yan's defeat resulted from believing fabricated intelligence.

The passage concludes by stressing that among military affairs, espionage requires the commander's personal oversight. Du Mu states intelligence operations must be directed by the commander from his private tent. Du You warns that without generous treatment, spies may defect to the enemy. Both Mei Yaochen and Wang Xi agree that receiving intelligence reports constitutes the commander's most confidential duty.

Through these annotated examples, the text reveals the complexity and significance of ancient military intelligence work, highlighting both the specialized qualities required of spies and the absolute necessity of the commander's personal control over this most secretive operation.

This passage discusses the wisdom of "using spies" (yongjian) in ancient warfare. Several military strategists emphasized that spies must be treated with exceptional closeness and trust, like one's own confidants. Rewards for spies should be extraordinarily generous, because the value of obtaining enemy intelligence far exceeds monetary costs—for instance, Chen Ping once proposed spending four hundred thousand jin of gold to bribe the officials of the Chu state.

Spy operations demand absolute secrecy; any leak could endanger one's own side. Only the general and the spy involved should know the details of the mission, as the saying goes: "From your mouth into my ears."

Employing spies requires supreme wisdom: First, one must assess whether the spy is honest and resourceful; second, one must cultivate benevolence and righteousness, winning their loyalty through kindness so they will serve wholeheartedly. Taigong (Jiang Ziya) said that practicing benevolence and righteousness attracts talented individuals to one's service—including potential spies. One must offer generous compensation while also treating them with genuine sincerity.

The text particularly notes that only meticulous discernment can verify the authenticity of intelligence. Since spies might provide false information for personal gain, extraordinary insight is needed to distinguish truth from deception. As the ancients said, "The human heart is more treacherous than mountains and rivers"—without sagely clarity, it is nearly impossible to see through such complexities.

This passage discusses the importance of using spies ("jian") to gather intelligence and related precautions.

First, it emphasizes that employing spies requires extremely subtle discernment to verify the authenticity of intelligence. Du You states that one must maintain absolute secrecy without leaks, while Mei Yaochen warns against spies being turned by the enemy, requiring meticulous consideration. Wang Xi points out that exceptional spies must possess keen insight. Zhang Yu concludes that when spies bring reports involving advantages and disadvantages, only profound and subtle discernment can determine their veracity.

Several commentators then stress the paramount importance of secrecy in intelligence operations. Du Mu asserts that every matter must be known beforehand; Mei Yaochen claims the more covert the operation, the more comprehensive the knowledge gained; Wang Xi insists on repeated emphasis to ensure thorough understanding of enemy situations; and Zhang Yu states that greater secrecy enables advance knowledge of all matters, both major and minor.

The text then addresses confidentiality protocols: if a spy's mission is exposed before execution, both the spy and whoever leaked the information must be executed. Du Mu explains this is because those who leak information, unless intentionally luring spies, wouldn't otherwise know the details. Chen Hao, Mei Yaochen and others agree this prevents information breaches, while He Shi notes military secrets demand severe punishment for leaks. Zhang Yu cites the example of Qin forces using counterintelligence to make Zhao replace Lian Po—they strictly forbade leaking Bai Qi's appointment as commander, showing even executed operations require secrecy, let alone pending ones.

Finally, operational specifics: before attacking enemy troops, cities, or assassinating targets, spies must first identify the defending generals and key personnel (such as reception officers, gatekeepers, and aides). Li Quan states knowing names makes success easier. Du Mu adds that before battle, one must understand enemy personnel's capabilities to respond appropriately—just as Emperor Gaozu of Han deployed Han Xin, Cao Shen and Guan Ying against Wei after assessing their talents.

Wei Bao (a general of the Wei state during the Warring States period) once asked his subordinates, "Who is the chief general of Wei?" They replied it was Bai Zhi. Upon hearing this, Liu Bang, the King of Han, remarked, "This man is still a greenhorn who can't possibly stand against Han Xin. Who commands their cavalry?" The answer was Feng Jing. Liu Bang commented, "He's the son of Ma Wuze, a surrendered general from Qin. Though somewhat capable, he's no match for Guan Ying. What about their infantry commander?" When told it was Xiang Tuo, Liu Bang declared, "This man is even less of a challenge for Cao Shen. Now I can rest easy."

Chen Hao, a Tang dynasty military strategist, observed that this passage emphasizes the necessity of thoroughly understanding the enemy's key commanders in advance—either by turning enemy spies or actively dispatching one's own agents. Without knowledge of the opposing leaders, effective espionage strategies cannot be implemented. For instance, when Liu Bang (later Emperor Gaozu of Han) attacked the Qin forces at Xiaoguan, his advisor Zhang Liang suggested, "I've heard the defending general Jia Jian is greedy. We can bribe him with substantial riches." He added, "Even if the general wishes to negotiate peace, his troops may not comply. We should strike when their guard is down." Liu Bang followed this advice and achieved victory.

Another example from the Spring and Autumn period involves Hua Yuan, a senior official of Song, who managed to sneak into the tent of Chu general Zi Fan at night to report Song's dire situation precisely because he had beforehand familiarized himself with the Chu army's camp layout and personnel. Du You, a Tang dynasty historian, elaborated: One must gather intelligence on all levels of the enemy's hierarchy—the officers in charge of military affairs (守官), messengers (谒者), gatekeepers (门者), and quartermasters (舍人). Only with this prior knowledge can one adapt swiftly in emergencies.

Mei Yaochen, a Song dynasty commentator, stressed the importance of detailed investigations into the names and positions of every level of the enemy's personnel, ensuring one's own spies are well-prepared for smooth operations. Wang Xi, a Song scholar, emphasized that such intelligence must be gathered beforehand, not on the battlefield. Zhang Yu, another annotator, further explained: Whether for military assaults or covert infiltration, key figures like city defense commanders, protocol officers, guards, and internal administrators must be identified in advance. Just as Hua Yuan could visit Zi Fan at night, or Liu Bang could enter Han Xin's chamber to seize his military tally, success relied on prior intelligence.

Lastly, regarding enemy spies: one should identify and capture them, then use generous bribes to turn them into double agents before sending them back. Du You clarified that "舍" (sheltering) refers to harboring enemy spies with lavish incentives before redeploying them to serve one's own purposes.

This passage explains the application of the "reverse spy" tactic in military strategy. Cao Cao interprets "舍" (sheltering) as establishing arrangements, while Du Mu adds that enemy spies should be lured with substantial benefits and settled to serve our purposes. Du You emphasizes the crucial point of converting enemy spies into our own agents.

Mei Yaochen notes that we must first detect the spies sent by the enemy, then entice them with benefits and properly settle them, thereby turning them into our reverse spies. Wang Xi stresses the need for careful handling of these spies, using clever rhetoric and deep emotional appeals to move them, supplemented by heavy bribes and the threat of punishment—unless they are exceptionally loyal, most will eventually serve our cause.

Zhang Yu further elaborates that we should actively seek out enemy spies sent to scout us, luring them with generous rewards and settling them in place. The term "sheltering" means detaining these spies for extended periods to extract more intelligence through prolonged conversations. The passage later mentions that the four types of spies (local spies, internal spies, reverse spies, and expendable spies) all depend on reverse spies to be effective. Without detaining these individuals for in-depth discussions, we cannot fully grasp the enemy's situation.

Du Mu adds that if we can use benefits to turn enemy spies into reverse spies, the same method can be employed to manipulate local spies (commoners from the enemy state) and internal spies (officials within the enemy's ranks). He underscores that using spies requires a willingness to spend generously—stinginess with titles, wealth, and rewards while refusing to gather enemy intelligence is the height of foolishness.

Chen Hao argues that the key lies in enticing enemy spies to stay through benefits, thereby extracting information and using reverse spies to guide local and internal spies. Both Du You and Mei Yaochen point out that reverse spies allow us to identify which commoners and officials in the enemy state can be exploited. Zhang Yu concludes that reverse spies reveal which individuals in the enemy state are greedy for profit and which officials harbor conflicts, making them susceptible to manipulation.

Finally, the passage discusses "expendable spies" (those who deliver false intelligence to the enemy), who can be used to feed the adversary misleading information. The core idea is this: we must skillfully exploit enemy spies, using both material incentives and emotional persuasion to convert them into intelligence assets, thereby gaining control over broader spy networks.

This passage discusses the application of the "Five Spies" (wujian) in ancient military strategy. The most crucial is counterespionage (fanjian) — utilizing enemy spies to discern the opponent's strengths and weaknesses. Once this is achieved, living spies (shengjian) who shuttle back and forth can successfully complete their intelligence missions on schedule.

The ruler must thoroughly understand the operations of all five types of spies. Counterespionage holds paramount importance and must be rewarded generously, as the other four categories — local spies (xiangjian) who leverage native informants, internal spies (neijian) who subvert enemy officials, doomed spies (sijian) who deliberately deliver false intelligence at the risk of their lives, and living spies (shengjian) — all depend on intelligence provided by counterespionage to be effective.

Two historical examples are cited: the rise of the Shang dynasty was facilitated by Yi Yin (Yi Zhi), who had previously served the Xia court, and the Zhou dynasty's ascendancy relied on Jiang Ziya (Lü Ya), who once served the Shang. Neither betrayed their original states; rather, the Xia and Shang failed to employ these talents, allowing the Shang and Zhou to benefit from their wisdom. The text emphasizes that espionage requires individuals of extraordinary wisdom like Yi Yin and Jiang Ziya to be executed successfully.

The core principle is this: the art of espionage demands supreme intelligence, with counterespionage forming the foundation of any spy network and thus requiring special attention. Only by skillfully employing all five spies — particularly by generously rewarding counterespionage agents — can a ruler accurately grasp the enemy's situation.

Yi Yin was originally a minister of the Xia dynasty before defecting to Shang, while Lü Wang (Jiang Ziya) served the Shang court before assisting the Zhou dynasty. These two figures respectively helped King Tang of Shang and King Wu of Zhou pacify the realm through military force—actions that aligned with the Mandate of Heaven and popular sentiment. Their cases differ entirely from mere defections like Bozhou Li fleeing to Chu, Miao Benhuang defecting to Jin, Hu Yong remaining in Wu, or Shi Hui staying in Qin. Only enlightened rulers and capable generals, those who can employ superior wisdom in espionage, can achieve great accomplishments. This is the crux of military strategy—the entire army's movements depend on intelligence gathered by spies.

Li Quan observes that Sun Tzu's Art of War begins with "Initial Estimations" and concludes with "Employing Spies," emphasizing that victory cannot rely solely on brute force—generals must be prudent in this regard. Du Mu further explains that without understanding the enemy's situation, one must not rashly deploy troops, and to obtain such intelligence, spies must be employed—hence the entire army's dependence on espionage. Li Jing maintains that military success comes not through prayers to heaven and earth, but through human ingenuity. Historical methods of espionage were manifold: some sowed discord between rulers, others between close advisors, between virtuous ministers, between capable officials, between allies, between neighboring states, between left and right attendants, or between vertical and horizontal strategists. Figures like Zigong, Shi Liao, Chen Zhen, Su Qin, Zhang Yi, and Fan Ju all achieved success through espionage.

There are five specific espionage techniques: First, employing locals to secretly observe and relay messages; second, using enemy officials to deliberately leak false information; third, manipulating enemy envoys to transmit misleading intelligence; fourth, carefully selecting agents to investigate enemy vulnerabilities; fifth, feigning criminal desertion to intentionally expose false plans to the enemy. All five methods require absolute secrecy and generous rewards—the more covert, the better. When dealing with a favored courtier in the enemy state, bribe them with treasures to satisfy their desires; when approaching a fallen minister, feign intimacy with substantial benefits to extract information; when encountering influential nobles fond of discussing gains and losses, send agents to flatter them and exploit their suspicions for counterintelligence; when receiving enemy envoys, deliberately delay receptions to observe their true intentions.

This passage discusses ancient strategies and precautions regarding espionage (using spies).

It first describes how to handle enemy envoys: outwardly receive them with warm hospitality, assign dedicated companions, while secretly arranging surveillance. When envoys stay too long and fear reprimand, they'll inevitably discuss confidential information privately—thus allowing valuable intelligence to be obtained. Espionage works both ways; since others will also employ spies against you, one must exercise careful judgment and comprehensive analysis to avoid miscalculations.

When enemies send spies to probe our actual situation, feign ignorance while treating them well, deliberately leaking false information—this enables counterintelligence manipulation. If the enemy misjudges our strength and weakness, we can seize victory. Just as water can both float and sink boats, espionage can succeed or fail.

The text then emphasizes the importance of loyalty: those truly devoted to their ruler act with integrity, avoiding underhanded schemes. Against such individuals, even the most skilled spies prove ineffective.

Finally, historical examples from the Spring and Autumn period are cited: When Bozhouli of Jin fled to Chu, and Miaobenhuang of Chu defected to Jin, both later advised their new states against their former homelands during the Yanling campaign. This illustrates how espionage requires meticulous talent selection and thorough intelligence analysis. Only sagacious rulers can effectively employ spies, for the virtuous willingly serve enlightened masters. If a ruler lacks benevolence and righteousness while suspecting capable advisors, even heaven won't bless them—let alone attract wise counselors. Hence the earlier assertions that "without sagely wisdom one cannot use spies" and "without humaneness and righteousness one cannot direct spies."

This content reveals the dialectical relationship between espionage and counterintelligence in ancient warfare, emphasizing that successful practitioners must cultivate wisdom, benevolence and other virtues to effectively wield this strategy without suffering countermeasures.

The enlightened rulers like King Tang of Shang and King Wu of Zhou achieved their great accomplishments precisely because they excelled in employing virtuous talents like Yi Yin (founding minister of Shang) and Lü Shang (Jiang Ziya, military strategist of Zhou's founding). When wise sovereigns meet worthy ministers, their harmony resembles the perfect interaction between Heaven and Earth, enabling their achievements to benefit the entire realm. Yet initially, these men might have been mere farmers tilling fields or elderly fishermen by the Wei River—who could have predicted their future greatness?

Jia Lin commented: An army without an intelligence network (the "five types of spies" refers to five reconnaissance methods) is like a person deprived of ears and eyes—incapable of action. Wang Xi noted: Without understanding the enemy's situation, one must never act rashly. Zhang Yu emphasized: The foundation of military operations lies in comprehending the enemy's condition, hence this constitutes the crux of warfare. Without knowing the enemy's actual strength and weakness, troops cannot be deployed—therefore the entire army's movements depend on intelligence.

This passage appears at the end of The Art of War's thirteen chapters because espionage doesn't belong to conventional military methods. Strategies like calculation, attack formations, situational assessment, and assessing strengths/weaknesses are employed whenever troops are mobilized—whereas fire attacks and espionage require opportune moments for implementation.

(Supplementary note: The "five types of spies" in The Art of War include: local spies [using enemy country villagers], internal spies [bribing enemy officials], reverse spies [turning enemy agents], doomed spies [delivering false intelligence], and surviving spies [those who return alive].)