The Art of War

 8. (3) When the force of the flames has reached its height,
    follow it up with an attack, if that is practicable;
    if not, stay where you are.

 9. (4) If it is possible to make an assault with fire
    from without, do not wait for it to break out within,
    but deliver your attack at a favorable moment.

10. (5) When you start a fire, be to windward of it. 
    Do not attack from the leeward.

11. A wind that rises in the daytime lasts long,
    but a night breeze soon falls.

12. In every army, the five developments connected with
    fire must be known, the movements of the stars calculated,
    and a watch kept for the proper days.

13. Hence those who use fire as an aid to the attack show intelligence;
    those who use water as an aid to the attack gain an accession of strength.

14. By means of water, an enemy may be intercepted,
    but not robbed of all his belongings.

15. Unhappy is the fate of one who tries to win his
    battles and succeed in his attacks without cultivating
    the spirit of enterprise; for the result is waste of time
    and general stagnation.

16. Hence the saying:  The enlightened ruler lays his
    plans well ahead; the good general cultivates his resources.

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.

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.

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; 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.


XIII. THE USE OF SPIES


 1. 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.

 2. 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
    of inhumanity.

 3. One who acts thus is no leader of men, no present
    help to his sovereign, no master of victory.

 4. 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.

 5. Now this foreknowledge cannot be elicited from spirits;
    it cannot be obtained inductively from experience,
    nor by any deductive calculation.

 6. Knowledge of the enemy's dispositions can only
    be obtained from other men.

 7. 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.

 8. 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.

 9. Having local spies means employing the services
    of the inhabitants of a district.