37. To begin by bluster, but afterwards to take fright at the enemy’s numbers, shows a supreme lack of intelligence.
[I follow the interpretation of Ts’ao Kung, also adopted by Li Ch’uan, Tu Mu, and Chang Yu. Another possible meaning set forth by Tu Yu, Chia Lin, Mei Tao-ch’en and Wang Hsi, is: "The general who is first tyrannical towards his men, and then in terror lest they should mutiny, etc." This would connect the sentence with what went before about rewards and punishments.]
38. When envoys are sent with compliments in their mouths, it is a sign that the enemy wishes for a truce.
[Tu Mu says: "If the enemy open friendly relations be sending hostages, it is a sign that they are anxious for an armistice, either because their strength is exhausted or for some other reason." But it hardly needs a Sun Tzŭ to draw such an obvious inference.]
39. If the enemy’s troops march up angrily and remain facing ours for a long time without either joining battle or taking themselves off again, the situation is one that demands great vigilance and circumspection.
[Ts’ao Kung says a manœuver of this sort may be only a ruse to gain time for an unexpected flank attack or the laying of an ambush.]
40. If our troops are no more in number than the enemy, that is amply sufficient; it only means that no direct attack can be made.
[Literally, "no martial advance." That is to say, cheng tactics and frontal attacks must be eschewed, and stratagem resorted to instead.]
What we can do is simply to concentrate all our available strength, keep a close watch on the enemy, and obtain reinforcements.
[This is an obscure sentence, and none of the commentators succeed in squeezing very good sense out of it. I follow Li Ch’uan, who appears to offer the simplest explanation: "Only the side that gets more men will win." Fortunately we have Chang Yu to expound its meaning to us in language which is lucidity itself: "When the numbers are even, and no favourable opening presents itself, although we may not be strong enough to deliver a sustained attack, we can find additional recruits amongst our sutlers and camp-followers, and then, concentrating our forces and keeping a close watch on the enemy, contrive to snatch the victory. But we must avoid borrowing foreign soldiers to help us." He then quotes from Wei Liao Tzŭ, ch. 3: "The nominal strength of mercenary troops may be 100,000, but their real value will be not more than half that figure.">[