XIII. THE USE OF SPIES
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. There will be commotion at home and abroad,
and men will drop down exhausted on the highways.
As many as seven hundred thousand families will be impeded
in their labor.
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, is the height
One who acts thus is no leader of men, no present
help to his sovereign, no master of victory.
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.
Now this foreknowledge cannot be elicited from spirits;
it cannot be obtained inductively from experience,
nor by any deductive calculation.
Knowledge of the enemy's dispositions can only
be obtained from other men.
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.
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.
Having local spies means employing the services
of the inhabitants of a district.
Having inward spies, making use of officials
of the enemy.
Having converted spies, getting hold of the enemy's
spies and using them for our own purposes.
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.
Surviving spies, finally, are those who bring
back news from the enemy's camp.
Hence it is that which none in the whole army are
more intimate relations to be maintained than with spies.
None should be more liberally rewarded. In no other
business should greater secrecy be preserved.
Spies cannot be usefully employed without a certain
They cannot be properly managed without benevolence
Without subtle ingenuity of mind, one cannot make
certain of the truth of their reports.
Be subtle! be subtle! and use your spies for every
kind of business.
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.
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, and door-keepers and sentries of the general
in command. Our spies must be commissioned to ascertain these.
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.
It is through the information brought by the
converted spy that we are able to acquire and employ
local and inward spies.
It is owing to his information, again, that we can
cause the doomed spy to carry false tidings to the enemy.
Lastly, it is by his information that the surviving
spy can be used on appointed occasions.
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.
Hence it is essential that the converted spy be treated
with the utmost liberality.
Of old, the rise of the Yin dynasty was due to I
Chih who had served under the Hsia. Likewise, the rise
of the Chou dynasty was due to Lu Ya who had served
under the Yin.
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. Spies are a most important element in water,
because on them depends an army's ability to move.
[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
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.