if quietly encamped, he can force him to move.
The subject to 能 is still 善戰者; but these clauses would read better as direct admonitions, and in the next sentence we find Sun Tzŭ dropping insensibly into the imperative.
5. 出其所必趨趨其所不意
Appear at points which the enemy must hasten to defend; march swiftly to places where you are not expected.
The original text, adopted by the T‘u Shu, has 出其所不趨; it has been altered to suit the context and the commentaries of Ts‘ao Kung and Ho Shih, who evidently read 必趨. The other reading would mean: “Appear at points to which the enemy cannot hasten;” but in this case there is something awkward in the use of 趨. Capt. Calthrop is wrong of course with “appearing where the enemy is not.”
6. 行千里而不勞者行於無人之地也
An army may march great distances without distress, if it marches through country where the enemy is not.
We must beware of understanding 無人之地 as “uninhabited country.” Sun Tzŭ habitually uses 人 in the sense of 敵, e.g. supra, [§ 2]. Ts‘ao Kung sums up very well: 出空擊虛避其所守擊其不意 “Emerge from the void [q.d. like “a bolt from the blue”], strike at vulnerable points, shun places that are defended, attack in unexpected quarters.” The difference of meaning between 空 and 虛 is worth noting.
7. 攻而必取者攻其所不守也守而必固者守其所不攻也
You can be sure of succeeding in your attacks if you only attack places which are undefended.