[This extremely concise expression is intelligibly paraphrased by Chia Lin: "even though we have constructed neither wall nor ditch." Li Ch’uan says: "we puzzle him by strange and unusual dispositions;" and Tu Mu finally clinches the meaning by three illustrative anecdotes—one of Chu-ko Liang, who when occupying Yang-p’ing and about to be attacked by Ssu-ma I, suddenly struck his colors, stopped the beating of the drums, and flung open the city gates, showing only a few men engaged in sweeping and sprinkling the ground. This unexpected proceeding had the intended effect; for Ssu-ma I, suspecting an ambush, actually drew off his army and retreated. What Sun Tzŭ is advocating here, therefore, is nothing more nor less than the timely use of "bluff."] 13. By discovering the enemy’s dispositions and remaining invisible ourselves, we can keep our forces concentrated, while the enemy’s must be divided. [The conclusion is perhaps not very obvious, but Chang Yu (after Mei Yao-ch’en) rightly explains it thus: "If the enemy’s dispositions are visible, we can make for him in one body; whereas, our own dispositions being kept secret, the enemy will be obliged to divide his forces in order to guard against attack from every quarter."] 14. We can form a single united body, while the enemy must split up into fractions. Hence there will be a whole pitted against separate parts of a whole, which means that we shall be many to the enemy’s few. 15. And if we are able thus to attack an inferior force with a superior one, our opponents will be in dire straits. 16. The spot where we intend to fight must not be made known; for then the enemy will have to prepare against a possible attack at several different points; [Sheridan once explained the reason of General Grant’s victories by saying that "while his opponents were kept fully employed wondering what he was going to do, _he_ was thinking most of what he was going to do himself."] and his forces being thus distributed in many directions, the numbers we shall have to face at any given point will be proportionately few. 17. For should the enemy strengthen his van, he will weaken his rear; should he strengthen his rear, he will weaken his van; should he strengthen his left, he will weaken his right; should he strengthen his right, he will weaken his left. If he sends reinforcements everywhere, he will everywhere be weak. [In Frederick the Great’s _Instructions to his Generals_ we read: "A defensive war is apt to betray us into too frequent detachment. Those generals who have had but little experience attempt to protect every point, while those who are better acquainted with their profession, having only the capital object in view, guard against a decisive blow, and acquiesce in small misfortunes to avoid greater."] 18. Numerical weakness comes from having to prepare against possible attacks; numerical strength, from compelling our adversary to make these preparations against us.