Art of War 3.18

Li Ch‘üan cites the case of 苻堅 Fu Chien, prince of 秦 Ch‘in, who in 383 A.D. marched with a vast army against the 晉 Chin Emperor. When warned not to despise an enemy who could command the services of such men as 謝安 Hsieh An and 桓沖 Huan Ch‘ung, he boastfully replied: “I have the population of eight provinces at my back, infantry and horsemen to the number of one million; why, they could dam up the Yangtsze River itself by merely throwing their whips into the stream. What danger have I to fear?” Nevertheless, his forces were soon after disastrously routed at the 淝 Fei River, and he was obliged to beat a hasty retreat.

The modern text, represented by the 北堂書鈔 and T‘u Shu, has 必敗, which I should be inclined to adopt in preference to 殆 here, though the T‘ung Tien and Yü Lan both have the latter. Chang Yü offers the best commentary on 知彼知己. He says that these words “have reference to attack and defence: knowing the enemy enables you to take the offensive, knowing yourself enables you to stand on the defensive.” He adds: 攻是守之機守是攻之策 “Attack is the secret of defence; defence is the planning of an attack.” It would be hard to find a better epitome of the root-principle of war.