5. 將不通於九變之利者雖知地形不能得地之利矣
The general who does not understand these, may be well acquainted with the configuration of the country, yet he will not be able to turn his knowledge to practical account.
Literally, “get the advantage of the ground,” which means not only securing good positions, but availing oneself of natural advantages in every possible way. Chang Yü says: “Every kind of ground is characterised by certain natural features, and also gives scope for a certain variability of plan. How is it possible to turn these natural features to account unless topographical knowledge is supplemented by versatility of mind?”
6. 治兵不知九變之術雖知五利不能得人之用矣
So, the student of war who is unversed in the art of varying his plans, even though he be acquainted with the Five Advantages, will fail to make the best use of his men.
Ts‘ao Kung says that the 五利 are 下五事也 “the five things that follow;” but this cannot be right. We must rather look back to the five “variations” contained in [§ 3]. Chia Lin (who reads 五變 here to balance the 五利) tells us that these imply five obvious and generally advantageous lines of action, namely: “if a certain road is short, it must be followed; if an army is isolated, it must be attacked; if a town is in a parlous condition, it must be besieged; if a position can be stormed, it must be attempted; and if consistent with military operations, the ruler’s commands must be obeyed.” But there are circumstances which sometimes forbid a general to use these advantages. For instance, “a certain road may be the shortest way for him, but if he knows that it abounds in natural obstacles, or that the enemy has laid an ambush on it, he will not follow that road. A hostile force may be open to attack, but if he knows that it is hard-pressed and likely to fight with desperation, he will refrain from striking,” and so on. Here the 變 comes in to modify the 利, and hence we see the uselessness of knowing the one without the other—of having an eye for weaknesses in the enemy’s armour without being clever enough to recast one’s plans on the spur of the moment. Capt. Calthrop offers this slovenly translation: “In the management of armies, if the art of the Nine Changes be understood [sic], a knowledge of the Five Advantages is of no avail.”
7. 是故智者之慮必雜於利害
Hence in the wise leader’s plans, considerations of advantage and of disadvantage will be blended together.
“Whether in an advantageous position or a disadvantageous one,” says Ts‘ao Kung, “the opposite state should be always present to your mind.”
8. 雜於利而務可信也