What enables the wise sovereign and the good general to strike and conquer, and achieve things beyond the reach of ordinary men, is foreknowledge.
Now this foreknowledge cannot be elicited from spirits; it cannot be obtained inductively from experience, nor by any deductive calculation.
Knowledge of the enemy's dispositions can only be obtained from other men. [i.e., spies.]
Spies cannot be usefully employed without a certain intuitive sagacity.
They [spies] cannot be properly managed without benevolence and straightforwardness.
Without subtle ingenuity of mind, one cannot make certain of the truth of their reports.
Be subtle! be subtle! and use your spies for every kind of business.
When a general, unable to estimate the enemy's strength, allows an inferior force to engage a larger one, or hurls a weak detachment against a powerful one, and neglects to place picked soldiers in the front rank, the result must be rout.
He who knows things, and in fighting puts his knowledge into practice, will win his battles. He who knows them not, nor practices them, will surely be defeated.
Carefully compare the opposing army with your own, so that you may know where strength is superabundant and where it is deficient.
Based on text from "The Art of War."