Wang Hsi thinks that this means, not using the same stratagem twice. He says: 已行之事已施之謀當革易之不可再之.
he keeps the enemy without definite knowledge.
Note that 人 denotes the enemy, as opposed to the 士卒 of [§ 36]. Capt. Calthrop, not perceiving this, joins the two paragraphs into one. Chang Yü quotes 太白山人 as saying: 兵貴詭道者非止詭敵也抑詭我士卒使由而不使知之也 “The axiom, that war is based on deception, does not apply only to deception of the enemy. You must deceive even your own soldiers. Make them follow you, but without letting them know why.”
By shifting his camp and taking circuitous routes, he prevents the enemy from anticipating his purpose.
Wang Hsi paraphrases 易其居 as 處易者 “camp on easy ground,” and Chang Yü follows him, saying: 其居則去險而就易. But this is an utterly untenable view. For 迂其途, cf. VII. 4. Chia Lin, retaining his old interpretation of those words, is now obliged to explain 易其居 as “cause the enemy to shift his camp,” which is awkward in the extreme.
38. 帥與之期如登高而去其梯帥與之深入諸侯之地而發其機
At the critical moment, the leader of an army acts like one who has climbed up a height and then kicks away the ladder behind him.
I must candidly confess that I do not understand the syntax of 帥與之期, though the meaning is fairly plain. The difficulty has evidently been felt, for Tu Mu tells us that one text omits 期如. It is more likely, however, that a couple of characters have dropped out.
He carries his men deep into hostile territory before he shows his hand.
發其機, literally, “releases the spring” (see [V. § 15]), that is, takes some decisive step which makes it impossible for the army to return—like 項羽 Hsiang Yü, who sunk his ships after crossing a river. Ch‘ên Hao, followed by Chia Lin, understands the words less well as 發其心機 “puts forth every artifice at his command.” But 機 in this derived sense occurs nowhere else in Sun Tzŭ.