Tu Mu’s commentary shows what has to be supplied "in order to make sense out of 以數守之. He says: 必筭星𨇠之數守風起之日乃可發火 “We must make calculations as to the paths of the stars, and watch for the days on which wind will rise, before making our attack with fire.” Chang Yü seems to take 守 in the sense of 防: “We must not only know how to assail our opponents with fire, but also be on our guard against similar attacks from them.”
13. Hence those who use fire as an aid to the attack show intelligence;
I have not the least hesitation in rejecting the commentators’ explanation of 明 as = 明白. Thus Chang Yü says: 灼然可以取勝 “... will clearly [i.e. obviously] be able to gain the victory.” This is not only clumsy in itself, but does not balance 强 in the next clause. For 明; “intelligent,” cf. infra, § 16, and Lun Yü XII. 6.
those who use water as an aid to the attack gain an accession of strength.
Capt. Calthrop gives an extraordinary rendering of the paragraph: “...if the attack is to be assisted, the fire must be unquenchable. If water is to assist the attack, the flood must be overwhelming.”
14. 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𮎰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.”