13. The Use of Spies

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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."