16. 吾所與戰之地不可知不可知則敵所備者多敵所備者多則吾所與戰者寡矣
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. 故備前則後寡備後則前寡備左則右寡備右則左寡無所不備則無所不寡
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 smaller misfortunes to avoid greater.”
18. 寡者備人者也衆者使人備己者也
Numerical weakness comes from having to prepare against possible attacks; numerical strength, from compelling our adversary to make these preparations against us.
The highest generalship, in Col. Henderson’s words, is “to compel the enemy to disperse his army, and then to concentrate superior force against each fraction in turn.”