8. When these five kinds of spy are all at work, none can discover the secret system. This is called "divine manipulation of the threads." It is the sovereign's most precious faculty.
[Cromwell, one of the greatest and most practical of all cavalry leaders, had officers styled 'scout masters,' whose business it was to collect all possible information regarding the enemy, through scouts and spies, etc., and much of his success in war was traceable to the previous knowledge of the enemy's moves thus gained."  ]
9. Having LOCAL SPIES means employing the services of the inhabitants of a district.
[Tu Mu says: "In the enemy's country, win people over by kind treatment, and use them as spies."]
10. Having INWARD SPIES, making use of officials of the enemy.
[Tu Mu enumerates the following classes as likely to do good service in this respect: "Worthy men who have been degraded from office, criminals who have undergone punishment; also, favorite concubines who are greedy for gold, men who are aggrieved at being in subordinate positions, or who have been passed over in the distribution of posts, others who are anxious that their side should be defeated in order that they may have a chance of displaying their ability and talents, fickle turncoats who always want to have a foot in each boat. Officials of these several kinds," he continues, "should be secretly approached and bound to one's interests by means of rich presents. In this way you will be able to find out the state of affairs in the enemy's country, ascertain the plans that are being formed against you, and moreover disturb the harmony and create a breach between the sovereign and his ministers." The necessity for extreme caution, however, in dealing with "inward spies," appears from an historical incident related by Ho Shih: "Lo
Shang, Governor of I-Chou, sent his general Wei Po to attack the rebel Li Hsiung of Shu in his stronghold at
P`i. After each side had experienced a number of victories and defeats, Li Hsiung had recourse to the services of a certain
P`o-t`ai, a native of Wu-tu. He began to have him whipped until the blood came, and then sent him off to Lo
Shang, whom he was to delude by offering to cooperate with him from inside the city, and to give a fire signal at the right moment for making a general assault. Lo
Shang, confiding in these promises, march out all his best troops, and placed Wei Po and others at their head with orders to attack at P`o-t`ai's bidding. Meanwhile, Li Hsiung's general, Li
Hsiang, had prepared an ambuscade on their line of march; and P`o-t`ai, having reared long scaling-ladders against the city walls, now lighted the beacon-fire. Wei Po's men raced up on seeing the signal and began climbing the ladders as fast as they could, while others were drawn up by ropes lowered from above. More than a hundred of Lo Shang's soldiers entered the city in this way, every one of whom was forthwith beheaded. Li Hsiung then charged with all his forces, both inside and outside the city, and routed the enemy completely." [This happened in 303 A.D. I do not know where Ho Shih got the story from. It is not given in the biography of Li Hsiung or that of his father Li
T`e, CHIN SHU, ch. 120, 121.]
11. Having CONVERTED SPIES, getting hold of the enemy's spies and using them for our own purposes.
[By means of heavy bribes and liberal promises detaching them from the enemy's service, and inducing them to carry back false information as well as to spy in turn on their own countrymen. On the other hand, Hsiao
Shih-hsien says that we pretend not to have detected him, but contrive to let him carry away a false impression of what is going on. Several of the commentators accept this as an alternative definition; but that it is not what Sun Tzu meant is conclusively proved by his subsequent remarks about treating the converted spy generously
(ss. 21 sqq.). Ho Shih notes three occasions on which converted spies were used with conspicuous success: (1) by T`ien Tan in his defense of Chi-mo (see supra, p. 90); (2) by Chao She on his march to
O-yu (see p. 57); and by the wily Fan Chu in 260 B.C., when Lien P`o was conducting a defensive campaign against
Ch`in. The King of Chao strongly disapproved of Lien P`o's cautious and dilatory methods, which had been unable to avert a series of minor disasters, and therefore lent a ready ear to the reports of his spies, who had secretly gone over to the enemy and were already in Fan Chu's pay. They said: "The only thing which causes Ch`in anxiety is lest Chao Kua should be made general. Lien P`o they consider an easy opponent, who is sure to be vanquished in the long run." Now this Chao Kua was a sun of the famous Chao She. From his boyhood, he had been wholly engrossed in the study of war and military matters, until at last he came to believe that there was no commander in the whole Empire who could stand against him. His father was much disquieted by this overweening conceit, and the flippancy with which he spoke of such a serious thing as war, and solemnly declared that if ever Kua was appointed general, he would bring ruin on the armies of
Chao. This was the man who, in spite of earnest protests from his own mother and the veteran statesman Lin
Hsiang-ju, was now sent to succeed Lien P`o. Needless to say, he proved no match for the redoubtable Po Ch`i and the great military power of
Ch`in. He fell into a trap by which his army was divided into two and his communications cut; and after a desperate resistance lasting 46 days, during which the famished soldiers devoured one another, he was himself killed by an arrow, and his whole force, amounting, it is said, to 400,000 men, ruthlessly put to the sword.]
12. Having DOOMED SPIES, doing certain things openly for purposes of deception, and allowing our spies to know of them and report them to the enemy.
[Tu Yu gives the best exposition of the meaning: "We ostentatiously do thing calculated to deceive our own spies, who must be led to believe that they have been unwittingly disclosed. Then, when these spies are captured in the enemy's lines, they will make an entirely false report, and the enemy will take measures accordingly, only to find that we do something quite different. The spies will thereupon be put to death." As an example of doomed spies, Ho Shih mentions the prisoners released by Pan Ch`ao in his campaign against
Yarkand. (See p. 132.) He also refers to T`ang Chien, who in 630 A.D. was sent by T`ai Tsung to lull the Turkish Kahn Chieh-li into fancied security, until Li Ching was able to deliver a crushing blow against him. Chang Yu says that the Turks revenged themselves by killing T`ang
Chien, but this is a mistake, for we read in both the old and the New T`ang History
(ch. 58, fol. 2 and ch. 89, fol. 8 respectively) that he escaped and lived on until 656. Li I-chi played a somewhat similar part in 203 B.C., when sent by the King of Han to open peaceful negotiations with
Ch`i. He has certainly more claim to be described a "doomed spy", for the king of
Ch`i, being subsequently attacked without warning by Han Hsin, and infuriated by what he considered the treachery of Li I-chi, ordered the unfortunate envoy to be boiled alive.]
13. SURVIVING SPIES, finally, are those who bring back news from the enemy's camp.
[This is the ordinary class of spies, properly so called, forming a regular part of the army. Tu Mu says: "Your surviving spy must be a man of keen intellect, though in outward appearance a fool; of shabby exterior, but with a will of iron. He must be active, robust, endowed with physical strength and courage; thoroughly accustomed to all sorts of dirty work, able to endure hunger and cold, and to put up with shame and ignominy." Ho Shih tells the following story of Ta`hsi Wu of the Sui dynasty: "When he was governor of Eastern
Ch`in, Shen-wu of Ch`i made a hostile movement upon Sha-yuan. The Emperor T`ai Tsu [? Kao
Tsu] sent Ta-hsi Wu to spy upon the enemy. He was accompanied by two other men. All three were on horseback and wore the enemy's uniform. When it was dark, they dismounted a few hundred feet away from the enemy's camp and stealthily crept up to listen, until they succeeded in catching the passwords used in the army. Then they got on their horses again and boldly passed through the camp under the guise of night-watchmen; and more than once, happening to come across a soldier who was committing some breach of discipline, they actually stopped to give the culprit a sound cudgeling! Thus they managed to return with the fullest possible information about the enemy's dispositions, and received warm commendation from the Emperor, who in consequence of their report was able to inflict a severe defeat on his adversary."]
14. Hence it is that which none in the whole army are more intimate relations to be maintained than with spies.
[Tu Mu and Mei Yao-ch`en point out that the spy is privileged to enter even the general's private sleeping-tent.]
None should be more liberally rewarded. In no other business should greater secrecy be preserved.
[Tu Mu gives a graphic touch: all communication with spies should be carried "mouth-to-ear." The following remarks on spies may be quoted from
Turenne, who made perhaps larger use of them than any previous commander: "Spies are attached to those who give them most, he who pays them ill is never served. They should never be known to anybody; nor should they know one another. When they propose anything very material, secure their persons, or have in your possession their wives and children as hostages for their fidelity. Never communicate anything to them but what is absolutely necessary that they should know.  ]
15. Spies cannot be usefully employed without a certain intuitive sagacity.
[Mei Yao-ch`en says: "In order to use them, one must know fact from falsehood, and be able to discriminate between honesty and double-dealing." Wang Hsi in a different interpretation thinks more along the lines of "intuitive perception" and "practical intelligence." Tu Mu strangely refers these attributes to the spies themselves: "Before using spies we must assure ourselves as to their integrity of character and the extent of their experience and skill." But he continues: "A brazen face and a crafty disposition are more dangerous than mountains or rivers; it takes a man of genius to penetrate such." So that we are left in some doubt as to his real opinion on the passage."]
16. They cannot be properly managed without benevolence and straightforwardness.
[Chang Yu says: "When you have attracted them by substantial offers, you must treat them with absolute sincerity; then they will work for you with all their might."]
17. Without subtle ingenuity of mind, one cannot make certain of the truth of their reports.
[Mei Yao-ch`en says: "Be on your guard against the possibility of spies going over to the service of the enemy."]
18. Be subtle! be subtle! and use your spies for every kind of business.
19. If a secret piece of news is divulged by a spy before the time is ripe, he must be put to death together with the man to whom the secret was told.
[Word for word, the translation here is: "If spy matters are heard before [our plans] are carried out," etc. Sun Tzu's main point in this passage is: Whereas you kill the spy himself "as a punishment for letting out the secret," the object of killing the other man is only, as Ch`en Hao puts it, "to stop his mouth" and prevent news leaking any further. If it had already been repeated to others, this object would not be gained. Either way, Sun Tzu lays himself open to the charge of inhumanity, though Tu Mu tries to defend him by saying that the man deserves to be put to death, for the spy would certainly not have told the secret unless the other had been at pains to worm it out of him."]
20. Whether the object be to crush an army, to storm a city, or to assassinate an individual, it is always necessary to begin by finding out the names of the attendants, the aides-de- camp,
[Literally "visitors", is equivalent, as Tu Yu says, to "those whose duty it is to keep the general supplied with information," which naturally necessitates frequent interviews with him.]
and door-keepers and sentries of the general in command. Our spies must be commissioned to ascertain these.
[As the first step, no doubt towards finding out if any of these important functionaries can be won over by bribery.]
21. The enemy's spies who have come to spy on us must be sought out, tempted with bribes, led away and comfortably housed. Thus they will become converted spies and available for our service.
22. It is through the information brought by the converted spy that we are able to acquire and employ local and inward spies.
[Tu Yu says: "through conversion of the enemy's spies we learn the enemy's condition." And Chang Yu says: "We must tempt the converted spy into our service, because it is he that knows which of the local inhabitants are greedy of gain, and which of the officials are open to corruption."]
23. It is owing to his information, again, that we can cause the doomed spy to carry false tidings to the enemy.
[Chang Yu says, "because the converted spy knows how the enemy can best be deceived."]
24. Lastly, it is by his information that the surviving spy can be used on appointed occasions.
25. The end and aim of spying in all its five varieties is knowledge of the enemy; and this knowledge can only be derived, in the first instance, from the converted spy.
[As explained in
ss. 22-24. He not only brings information himself, but makes it possible to use the other kinds of spy to advantage.]
Hence it is essential that the converted spy be treated with the utmost liberality.
26. Of old, the rise of the Yin dynasty
[Sun Tzu means the Shang dynasty, founded in 1766 B.C. Its name was changed to Yin by P`an Keng in 1401.]
was due to I Chih
[Better known as I Yin, the famous general and statesman who took part in Ch`eng T`ang's campaign against Chieh
who had served under the
Hsia. Likewise, the rise of the Chou dynasty was due to Lu Ya
[Lu Shang rose to high office under the tyrant Chou
Hsin, whom he afterwards helped to overthrow. Popularly known as T`ai Kung, a title bestowed on him by Wen Wang, he is said to have composed a treatise on war, erroneously identified with the LIU
who had served under the Yin.
[There is less precision in the Chinese than I have thought it well to introduce into my translation, and the commentaries on the passage are by no means explicit. But, having regard to the context, we can hardly doubt that Sun Tzu is holding up I Chih and Lu Ya as illustrious examples of the converted spy, or something closely analogous. His suggestion is, that the Hsia and Yin dynasties were upset owing to the intimate knowledge of their weaknesses and shortcoming which these former ministers were able to impart to the other side. Mei Yao-ch`en appears to resent any such aspersion on these historic names: "I Yin and Lu
Ya," he says, "were not rebels against the Government. Hsia could not employ the former, hence Yin employed him. Yin could not employ the latter, hence Hou employed him. Their great achievements were all for the good of the people." Ho Shih is also indignant: "How should two divinely inspired men such as I and Lu have acted as common spies? Sun Tzu's mention of them simply means that the proper use of the five classes of spies is a matter which requires men of the highest mental caliber like I and Lu, whose wisdom and capacity qualified them for the task. The above words only emphasize this point." Ho Shih believes then that the two heroes are mentioned on account of their supposed skill in the use of spies. But this is very weak.]
27. Hence it is only the enlightened ruler and the wise general who will use the highest intelligence of the army for purposes of spying and thereby they achieve great results.
[Tu Mu closes with a note of warning: "Just as water, which carries a boat from bank to bank, may also be the means of sinking it, so reliance on spies, while production of great results, is oft-times the cause of utter destruction."]
Spies are a most important element in water, because on them depends an army's ability to move.
[Chia Lin says that an army without spies is like a man with ears or eyes.]
 "Aids to Scouting," p. 2.
 "Marshal Turenne," p. 311.