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, the door-keepers and sentries of the general in command. Our spies must be commissioned to ascertain these. 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. 23. It is owing to his information, again, that we can cause the doomed spy to carry false tidings to the enemy. 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. Hence it is essential that the converted spy be treated with the utmost liberality. 26. 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 Lü Ya who had served under the Yin. 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. Spies are a most important element in war, because on them depends an army’s ability to move.