17. When it was to their advantage, they made a forward move; when otherwise, they stopped still. 18. If asked how to cope with a great host of the enemy in orderly array and on the point of marching to the attack, I should say: “Begin by seizing something which your opponent holds dear; then he will be amenable to your will.” 19. Rapidity is the essence of war: take advantage of the enemy’s unreadiness, make your way by unexpected routes, and attack unguarded spots. 20. The following are the principles to be observed by an invading force: The further you penetrate into a country, the greater will be the solidarity of your troops, and thus the defenders will not prevail against you. 21. Make forays in fertile country in order to supply your army with food. 22. Carefully study the well-being of your men, and do not overtax them. Concentrate your energy and hoard your strength. Keep your army continually on the move, and devise unfathomable plans. 23. Throw your soldiers into positions whence there is no escape, and they will prefer death to flight. If they will face death, there is nothing they may not achieve. Officers and men alike will put forth their uttermost strength. 24. Soldiers when in desperate straits lose the sense of fear. If there is no place of refuge, they will stand firm. If they are in the heart of a hostile country, they will show a stubborn front. If there is no help for it, they will fight hard. 25. Thus, without waiting to be marshalled, the soldiers will be constantly on the _qui vive;_ without waiting to be asked, they will do your will; without restrictions, they will be faithful; without giving orders, they can be trusted. 26. Prohibit the taking of omens, and do away with superstitious doubts. Then, until death itself comes, no calamity need be feared. 27. If our soldiers are not overburdened with money, it is not because they have a distaste for riches; if their lives are not unduly long, it is not because they are disinclined to longevity. 28. On the day they are ordered out to battle, your soldiers may weep, those sitting up bedewing their garments, and those lying down letting the tears run down their cheeks. But let them once be brought to bay, and they will display the courage of a Chu or a Kuei. 29. The skilful tactician may be likened to the _shuai-jan_. Now the _shuai-jan_ is a snake that is found in the Ch‘ang mountains. Strike at its head, and you will be attacked by its tail; strike at its tail, and you will be attacked by its head; strike at its middle, and you will be attacked by head and tail both. 30. Asked if an army can be made to imitate the _shuai-jan_, I should answer, Yes. For the men of Wu and the men of Yüeh are enemies; yet if they are crossing a river in the same boat and are caught by a storm, they will come to each other’s assistance just as the left hand helps the right.