[Tu Mu quotes the following from the _San Lueh_, ch. 2: "The warlike prince controls his soldiers by his authority, kits them together by good faith, and by rewards makes them serviceable. If faith decays, there will be disruption; if rewards are deficient, commands will not be respected."] 17. Move not unless you see an advantage; use not your troops unless there is something to be gained; fight not unless the position is critical. [Sun Tzŭ may at times appear to be over-cautious, but he never goes so far in that direction as the remarkable passage in the _Tao Te Ching_, ch. 69. "I dare not take the initiative, but prefer to act on the defensive; I dare not advance an inch, but prefer to retreat a foot."] 18. No ruler should put troops into the field merely to gratify his own spleen; no general should fight a battle simply out of pique. 19. If it is to your advantage, make a forward move; if not, stay where you are. [This is repeated from XI. § 17. Here I feel convinced that it is an interpolation, for it is evident that § 20 ought to follow immediately on § 18.] 20. Anger may in time change to gladness; vexation may be succeeded by content. 21. But a kingdom that has once been destroyed can never come again into being; [The Wu State was destined to be a melancholy example of this saying.] nor can the dead ever be brought back to life. 22. Hence the enlightened ruler is heedful, and the good general full of caution. This is the way to keep a country at peace and an army intact. [1] "Unless you enter the tiger’s lair, you cannot get hold of the tiger’s cubs." Chapter XIII. THE USE OF SPIES 1. Sun Tzŭ 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. §§ 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.