the expediency of aggressive or defensive tactics; and the fundamental laws of human nature: these are things that must most certainly be studied.
42. When invading hostile territory, the general principle is, that penetrating deeply brings cohesion; penetrating but a short way means dispersion.
[Cf. supra, § 20.]
43. When you leave your own country behind, and take your army across neighbourhood territory, you find yourself on critical ground.
[This "ground" is curiously mentioned in VIII. § 2, but it does not figure among the Nine Situations or the Six Calamities in chap. X. One’s first impulse would be to translate it distant ground," but this, if we can trust the commentators, is precisely what is not meant here. Mei Yao-ch’en says it is "a position not far enough advanced to be called ‘facile,’ and not near enough to home to be ‘dispersive,’ but something between the two." Wang Hsi says: "It is ground separated from home by an interjacent state, whose territory we have had to cross in order to reach it. Hence, it is incumbent on us to settle our business there quickly." He adds that this position is of rare occurrence, which is the reason why it is not included among the Nine Situations.]
When there are means of communication on all four sides, the ground is one of intersecting highways.
44. When you penetrate deeply into a country, it is serious ground. When you penetrate but a little way, it is facile ground.
45. When you have the enemy’s strongholds on your rear, and narrow passes in front, it is hemmed-in ground. When there is no place of refuge at all, it is desperate ground.
46. Therefore, on dispersive ground, I would inspire my men with unity of purpose.
[This end, according to Tu Mu, is best attained by remaining on the defensive, and avoiding battle. Cf. supra, § 11.]