8. 故用兵之法十則圍之五則攻之倍則分之
It is the rule in war, if our forces are ten to the enemy’s one, to surround him; if five to one, to attack him;
Straightaway, without waiting for any further advantage.
if twice as numerous, to divide our army into two.
Note that 之 does not refer to the enemy, as in the two preceding clauses. This sudden change of object is quite common in Chinese. 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: 以二敵一則一術爲正一術爲奇 “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.” [For explanation of 正 and 奇, see V. 3, note.] Chang Yü 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.”
9. 敵則能戰之少則能逃之不若則能避之
If equally matched, we can offer battle;
Li Ch‘üan, followed by Ho Shih, gives the following paraphrase: 主客力敵惟善者戰 “If attackers and attacked are equally matched in strength, only the able general will fight.” He thus takes 能 as though it were 能者, which is awkward.
if slightly inferior in numbers, we can avoid the enemy;
The T‘u Shu has 守 instead of 逃, which is hardly distinguishable in sense from 避 in the next clause. The meaning, “we can watch the enemy,” is certainly a great improvement on the above; but unfortunately there appears to be no very good authority for the variant. Chang Yü reminds us that the saying only applies if the other factors are equal; a small difference in numbers is often more than counterbalanced by superior energy and discipline.