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Ch‘ên Hao compares § 15: 非聖智不能用間. He points out that 湯武之聖伊呂宜用 “the god-like wisdom of Ch‘êng T‘ang and Wu Wang led them to employ I Yin and Lü Shang.” The T‘u Shu omits 惟.
and thereby they achieve great results.
Tu Mu closes with a note of warning: 夫水所以能濟舟亦有因水而覆沒者間所以能成功亦有憑間而傾敗者 “Just as water, which carries a boat from bank to bank, may also be the means of sinking it, so reliance on spies, while productive of great results, is oft-times the cause of utter destruction.”
Spies are a most important element in war, because on them depends an army’s ability to move.
The antecedent to 此 must be either 間者 or 用間者 understood from the whole sentence. Chia Lin says that an army without spies is like a man without ears or eyes.