13. The Use of Spies
Now this foreknowledge cannot be elicited from spirits; it cannot be obtained inductively from experience,
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."