[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 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 LIU T`AO.]
who had served under the Yin.
