By means of water, an enemy may be intercepted, but not robbed of all
his belongings.
Ts‘ao Kung’s note is: 但可以絶敵道分敵軍不可以奪敵蓄積 “We can merely
obstruct the enemy’s road or divide his army, but not sweep away
all his accumulated stores.” Water can do useful service, but it
lacks the terrible destructive power of fire. This is the reason,
Chang Yü concludes, why the former is dismissed in a couple of
sentences, whereas the attack by fire is discussed in detail. Wu
Tzŭ (ch. 4) speaks thus of the two elements: 居軍下濕水無所通霖雨數至
可灌而沉居軍荒澤草楚幽穢風飆數至可焚而滅 “If an army is encamped on
low-lying marshy ground, from which the water cannot run off, and
where the rainfall is heavy, it may be submerged by a flood. If an
army is encamped in wild marsh lands thickly overgrown with weeds
and brambles, and visited by frequent gales, it may be
exterminated by fire.”