The original text omits 藏, which has been restored from the T‘ung Tien and Yü Lan. The T‘u Shu omits 處 as well, making 所 a substantive. On 姦 Chang Yü has the note: 又慮姦細潛隱覘我虛實聽我號令伏姦當爲兩事 “We must also be on our guard against traitors who may lie in close covert, secretly spying out our weaknesses and overhearing our instructions. Fu and chien are to be taken separately.”
18. 敵近而靜者恃其險也
When the enemy is close at hand and remains quiet, he is relying on the natural strength of his position.
Here begin Sun Tzŭ’s remarks on the reading of signs, much of which is so good that it could almost be included in a modern manual like Gen. Baden-Powell’s “Aids to Scouting.”
19. 遠而挑戰者欲人之進也
When he keeps aloof and tries to provoke a battle, he is anxious for the other side to advance.
Probably because we are in a strong position from which he wishes to dislodge us. “If he came close up to us,” says Tu Mu, “and tried to force a battle, he would seem to despise us, and there would be less probability of our responding to the challenge.”
20. 其所居者易利也
If his place of encampment is easy of access, he is tendering a bait.
易 is here the opposite of 險 in [§ 18]. The reading of the T‘ung Tien and Yü Lan, 其所處者居易利也, is pretty obviously corrupt. The original text, which transposes 易 and 者, may very possibly be right. Tu Mu tells us that there is yet another reading: 士爭其所居者易利也.