20. But if neither time nor place be known, then the left wing will be impotent to succour the right, the right equally impotent to succour the left, the van unable to relieve the rear, or the rear to support the van. How much more so if the furthest portions of the army are anything under a hundred li apart, and even the nearest are separated by several li!
[The Chinese of this last sentence is a little lacking in precision, but the mental picture we are required to draw is probably that of an army advancing towards a given rendezvous in separate columns, each of which has orders to be there on a fixed date. If the general allows the various detachments to proceed at haphazard, without precise instructions as to the time and place of meeting, the enemy will be able to annihilate the army in detail. Chang Yu’s note may be worth quoting here: "If we do not know the place where our opponents mean to concentrate or the day on which they will join battle, our unity will be forfeited through our preparations for defence, and the positions we hold will be insecure. Suddenly happening upon a powerful foe, we shall be brought to battle in a flurried condition, and no mutual support will be possible between wings, vanguard or rear, especially if there is any great distance between the foremost and hindmost divisions of the army.">[
21. Though according to my estimate the soldiers of Yüeh exceed our own in number, that shall advantage them nothing in the matter of victory. I say then that victory can be achieved.
[Alas for these brave words! The long feud between the two states ended in 473 B.C. with the total defeat of Wu by Kou Chien and its incorporation in Yüeh. This was doubtless long after Sun Tzŭ’s death. With his present assertion compare IV. § 4. Chang Yu is the only one to point out the seeming discrepancy, which he thus goes on to explain: "In the chapter on Tactical Dispositions it is said, ‘One may know how to conquer without being able to do it,’ whereas here we have the statement that ‘victory’ can be achieved.’ The explanation is, that in the former chapter, where the offensive and defensive are under discussion, it is said that if the enemy is fully prepared, one cannot make certain of beating him. But the present passage refers particularly to the soldiers of Yüeh who, according to Sun Tzŭ’s calculations, will be kept in ignorance of the time and place of the impending struggle. That is why he says here that victory can be achieved.">[
22. Though the enemy be stronger in numbers, we may prevent him from fighting. Scheme so as to discover his plans and the likelihood of their success.
[An alternative reading offered by Chia Lin is: "Know beforehand all plans conducive to our success and to the enemy’s failure."
23. Rouse him, and learn the principle of his activity or inactivity.
[Chang Yu tells us that by noting the joy or anger shown by the enemy on being thus disturbed, we shall be able to conclude whether his policy is to lie low or the reverse. He instances the action of Cho-ku Liang, who sent the scornful present of a woman’s head-dress to Ssu-ma I, in order to goad him out of his Fabian tactics.]
Force him to reveal himself, so as to find out his vulnerable spots.
24. Carefully compare the opposing army with your own, so that you may know where strength is superabundant and where it is deficient.