[Tu Mu’s note is: "[knowledge of the enemy] cannot be gained by reasoning from other analogous cases."] nor by any deductive calculation. [Li Ch’uan says: "Quantities like length, breadth, distance and magnitude, are susceptible of exact mathematical determination; human actions cannot be so calculated."] 6. Knowledge of the enemy’s dispositions can only be obtained from other men. [Mei Yao-ch’en has rather an interesting note: "Knowledge of the spirit-world is to be obtained by divination; information in natural science may be sought by inductive reasoning; the laws of the universe can be verified by mathematical calculation: but the dispositions of an enemy are ascertainable through spies and spies alone."] 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. [Cromwell, one of the greatest and most practical of all cavalry leaders, had officers styled ‘scout masters,’ whose business it was to collect all possible information regarding the enemy, through scouts and spies, etc., and much of his success in war was traceable to the previous knowledge of the enemy’s moves thus gained." [1] ] 9. Having _local spies_ means employing the services of the inhabitants of a district. [Tu Mu says: "In the enemy’s country, win people over by kind treatment, and use them as spies."] 10. Having _inward spies_, making use of officials of the enemy.