Art of War 11.65

This looks a very simple sentence, yet Ts‘ao Kung is the only commentator who takes it as I have done. Mêng Shih, followed by Mei Yao-ch‘ên and Chang Yü, defines 開闔 as 間者 “spies,” and makes 入 an active verb: “If spies come from the enemy, we must quickly let them in.” But I cannot find that the words 開闔 have this meaning anywhere else. On the other hand, they may be taken as two verbs, 或開或闔, expressing the enemy’s indecision whether to advance or retreat, that being the best moment to attack him. [Cf. Tao Tê Ching, chap. X: 天門開闔能爲雌乎; also Li Chi, 曲禮, I. ii. 25.] It is not easy to choose between this and Ts‘ao Kung’s explanation; the fact that 敵人開戶 occurs shortly afterwards, in § 68, might be adduced in support of either. 必 must be understood in the sense of 宜 or 當. The only way to avoid this is to put 開闔 between commas and translate: “If we leave a door open, the enemy is sure to rush in.”