The sovereign must have full knowledge of the activities of the five sorts of agents. This knowledge must come from the double agents, and therefore it is mandatory that they be treated with the utmost liberality.

If an enemy has alliances, the problem is grave and the enemy's position strong; if he has no alliances, the problem is minor and the enemy's position weak.

It is ten thousand times cheaper to pay the best spies lavishly than even a tiny army poorly.

He will win who knows when to fight and when not to fight.

So a military force has no constant formation, water has no constant shape: the ability to gain victory by changing and adapting according to the opponent is called genius.

Bring war material with you from home, but forage on the enemy... use the conquered foe to augment one's own strength.

Attack where he is unprepared; sally forth when he does not expect you.