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if twice as numerous, to divide our army into two.

[Tu Mu takes exception to the saying; and at first sight, indeed,

it appears to violate a fundamental principle of war. Ts'ao Kung,

however, gives a clue to Sun Tzŭ's meaning: "Being two to the

enemy's one, we may use one part of our army in the regular way,

and the other for some special diversion." Chang Yu thus further

elucidates the point: "If our force is twice as numerous as that

of the enemy, it should be split up into two divisions, one to

meet the enemy in front, and one to fall upon his rear; if he

replies to the frontal attack, he may be crushed from behind; if

to the rearward attack, he may be crushed in front." This is what

is meant by saying that 'one part may be used in the regular way,

and the other for some special diversion.' Tu Mu does not

understand that dividing one's army is simply an irregular, just

as concentrating it is the regular, strategical method, and he is

too hasty in calling this a mistake."]