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.”