29. Military tactics are like unto water; for water in its natural course runs away from high places and hastens downwards.
行 is 劉晝子 Liu Chou-tzŭ’s reading for 形 in the original text.
30. So in war, the way is to avoid what is strong and to strike at what is weak.
Like water, taking the line of least resistance.
31. Water shapes its course according to the nature of the ground over which it flows;
The T‘ung Tien and Yü Lan read 制形, — the latter also 制行. The present text is derived from Chêng Yu-hsien.
the soldier works out his victory in relation to the foe whom he is facing.
32. Therefore, just as water retains no constant shape, so in warfare there are no constant conditions.
33. He who can modify his tactics in relation to his opponent and thereby succeed in winning, may be called a heaven-born captain.
34. The five elements
Water, fire, wood, metal, earth.
are not always equally predominant;
That is, as Wang Hsi says: 迭相克也 “they predominate alternately.”