You can ensure the safety of your defence if you only hold positions that cannot be attacked. [_I.e._, where there are none of the weak points mentioned above. There is rather a nice point involved in the interpretation of this later clause. Tu Mu, Ch’en Hao, and Mei Yao-ch’en assume the meaning to be: "In order to make your defence quite safe, you must defend _even_ those places that are not likely to be attacked;" and Tu Mu adds: "How much more, then, those that will be attacked." Taken thus, however, the clause balances less well with the preceding—always a consideration in the highly antithetical style which is natural to the Chinese. Chang Yu, therefore, seems to come nearer the mark in saying: "He who is skilled in attack flashes forth from the topmost heights of heaven [see IV. § 7], making it impossible for the enemy to guard against him. This being so, the places that I shall attack are precisely those that the enemy cannot defend…. He who is skilled in defence hides in the most secret recesses of the earth, making it impossible for the enemy to estimate his whereabouts. This being so, the places that I shall hold are precisely those that the enemy cannot attack."] 8. Hence that general is skilful in attack whose opponent does not know what to defend; and he is skilful in defence whose opponent does not know what to attack. [An aphorism which puts the whole art of war in a nutshell.] 9. O divine art of subtlety and secrecy! Through you we learn to be invisible, through you inaudible; [Literally, "without form or sound," but it is said of course with reference to the enemy.] and hence we can hold the enemy’s fate in our hands. 10. You may advance and be absolutely irresistible, if you make for the enemy’s weak points; you may retire and be safe from pursuit if your movements are more rapid than those of the enemy. 11. If we wish to fight, the enemy can be forced to an engagement even though he be sheltered behind a high rampart and a deep ditch. All we need do is attack some other place that he will be obliged to relieve. [Tu Mu says: "If the enemy is the invading party, we can cut his line of communications and occupy the roads by which he will have to return; if we are the invaders, we may direct our attack against the sovereign himself." It is clear that Sun Tzŭ, unlike certain generals in the late Boer war, was no believer in frontal attacks.] 12. If we do not wish to fight, we can prevent the enemy from engaging us even though the lines of our encampment be merely traced out on the ground. All we need do is to throw something odd and unaccountable in his way.