Mei Yao-ch‘ên has rather an interesting note: 鬼神之情可以筮卜知形氣之 物可以象類求天地之理可以度數驗唯敵之情必由間者而後知也 “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. 故用間有五有鄉間有內間有反間有死間有生間 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. 五間俱起莫知其道是謂神紀人君之寳也 When these five kinds of spy are all at work, none can discover the secret system. 道 is explained by Tu Mu as 其情泄形露之道 “the way in which facts leak out and dispositions are revealed.” This is called 爲 is the reading of the standard text, but the _T‘ung Tien_, _Yü Lan_ and _T‘u Shu_ all have 謂. “divine manipulation of the threads.” Capt. Calthrop translates 神紀 “the Mysterious Thread,” but Mei Yao-ch‘ên’s paraphrase 神妙之綱紀 shows that what is meant is the _control_ of a number of 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.”[184] 9. 鄉間者因其鄉人而用之 Having _local spies_ 鄉間 is the emended reading of Chia Lin and the _T‘u Shu_ for the unintelligible 因間, here and in § 7, of the standard text, which nevertheless reads 鄉間 in § 22. 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. 內間者因其官人而用之 Having _inward spies_, making use of officials of the enemy.