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The Art of War - Chapter 13. The Use of Spies

1. Introduction

2. The Text of Sun Tzu

3. The Commentators

4. Appreciations of Sun Tzu

5. Apologies for War

6. Bibliography

7. Footnotes

8. Chapter 1. Laying Plans

9. Chapter 2. Waging War

10. Chapter 3. Attack By Stratagem

11. Chapter 4. Tactical Disposition

12. Chapter 5. Energy

13. Chapter 6. Weak Points and Strong

14. Chapter 7. Manuevering

15. Chapter 8. Variations in Tactics

16. Chapter 9. The Army on the March

17. Chapter 10. Terrain

18. Chapter 11. The Nine Situations

19. Chapter 12. The Attack by Fire

20. Chapter 13. The Use of Spies


1. Sun Tzu said: Raising a host of a hundred thousand men
and marching them great distances entails heavy loss on the
people and a drain on the resources of the State. The daily
expenditure will amount to a thousand ounces of silver.

[Cf. II. ss. ss. 1, 13, 14.]

There will be commotion at home and abroad, and men will drop
down exhausted on the highways.

[Cf. TAO TE CHING, ch. 30: "Where troops have been
quartered, brambles and thorns spring up. Chang Yu has the note:
"We may be reminded of the saying: 'On serious ground, gather in
plunder.' Why then should carriage and transportation cause
exhaustion on the highways?--The answer is, that not victuals
alone, but all sorts of munitions of war have to be conveyed to
the army. Besides, the injunction to 'forage on the enemy' only
means that when an army is deeply engaged in hostile territory,
scarcity of food must be provided against. Hence, without being
solely dependent on the enemy for corn, we must forage in order
that there may be an uninterrupted flow of supplies. Then,
again, there are places like salt deserts where provisions being
unobtainable, supplies from home cannot be dispensed with."]

As many as seven hundred thousand families will be impeded in
their labor.

[Mei Yao-ch`en says: "Men will be lacking at the plough-
tail." The allusion is to the system of dividing land into nine
parts, each consisting of about 15 acres, the plot in the center
being cultivated on behalf of the State by the tenants of the
other eight. It was here also, so Tu Mu tells us, that their
cottages were built and a well sunk, to be used by all in common.
[See II. ss. 12, note.] In time of war, one of the families had
to serve in the army, while the other seven contributed to its
support. Thus, by a levy of 100,000 men (reckoning one able-
bodied soldier to each family) the husbandry of 700,000 families
would be affected.]

2. Hostile armies may face each other for years, striving
for the victory which is decided in a single day. This being so,
to remain in ignorance of the enemy's condition simply because
one grudges the outlay of a hundred ounces of silver in honors
and emoluments,

["For spies" is of course the meaning, though it would spoil
the effect of this curiously elaborate exordium if spies were
actually mentioned at this point.]

is the height of inhumanity.

[Sun Tzu's agreement is certainly ingenious. He begins by
adverting to the frightful misery and vast expenditure of blood
and treasure which war always brings in its train. Now, unless
you are kept informed of the enemy's condition, and are ready to
strike at the right moment, a war may drag on for years. The
only way to get this information is to employ spies, and it is
impossible to obtain trustworthy spies unless they are properly
paid for their services. But it is surely false economy to
grudge a comparatively trifling amount for this purpose, when
every day that the war lasts eats up an incalculably greater sum.
This grievous burden falls on the shoulders of the poor, and
hence Sun Tzu concludes that to neglect the use of spies is
nothing less than a crime against humanity.]

3. One who acts thus is no leader of men, no present help
to his sovereign, no master of victory.

[This idea, that the true object of war is peace, has its
root in the national temperament of the Chinese. Even so far
back as 597 B.C., these memorable words were uttered by Prince
Chuang of the Ch`u State: "The [Chinese] character for 'prowess'
is made up of [the characters for] 'to stay' and 'a spear'
(cessation of hostilities). Military prowess is seen in the
repression of cruelty, the calling in of weapons, the
preservation of the appointment of Heaven, the firm establishment
of merit, the bestowal of happiness on the people, putting
harmony between the princes, the diffusion of wealth."]

4. Thus, what enables the wise sovereign and the good
general to strike and conquer, and achieve things beyond the
reach of ordinary men, is FOREKNOWLEDGE.

[That is, knowledge of the enemy's dispositions, and what he
means to do.]

5. Now this foreknowledge cannot be elicited from spirits;
it cannot be obtained inductively from experience,

[Tu Mu's note is: "[knowledge of the enemy] cannot be
gained by reasoning from other analogous cases."]

nor by any deductive calculation.

[Li Ch`uan says: "Quantities like length, breadth,
distance and magnitude, are susceptible of exact mathematical
determination; human actions cannot be so calculated."]

6. Knowledge of the enemy's dispositions can only be
obtained from other men.

[Mei Yao-ch`en has rather an interesting note: "Knowledge
of the spirit-world is to be obtained by divination; information
in natural science may be sought by inductive reasoning; the laws
of the universe can be verified by mathematical calculation: but
the dispositions of an enemy are ascertainable through spies and
spies alone."]

7. Hence the use of spies, of whom there are five classes:
(1) Local spies; (2) inward spies; (3) converted spies; (4)
doomed spies; (5) surviving spies.
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." [1] ]

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

[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

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. [2] ]

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

16. They cannot be properly managed without benevolence and

[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.

[Cf. VI. ss. 9.]

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

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-

[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
22. It is through the information brought by the converted
spy that we are able to acquire and employ local and inward

[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

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 Kuei.]

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

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.]

[1] "Aids to Scouting," p. 2.

[2] "Marshal Turenne," p. 311.

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