九地篇 NO.4：
故善用兵者，譬如率然。率然者，常山之蛇也。
击其首则尾至，击其尾则首至，击其中则首尾俱至。敢问兵可使如率然乎？曰可。
夫吴人与越人相恶也，当其同舟而济而遇风，其相救也如左右手。
是故方马埋轮，未足恃也；齐勇如一，政之道也；刚柔皆得，地之理也。
故善用兵者，携手若使一人，不得已也。
这句啥意思：
善于指挥作战的人，能使部队自我策应如同“率然”蛇一样。
“率然”是常山地方一种蛇，打它的头部，尾巴就来救应；打它的尾，头就来救应；打它的腰，头尾都来救应。
试问：可以使军队象“率然”一样吧？回答是：可以。
那吴国人和越国人是互相仇视的，但当他们同船渡河而遇上大风时，他们相互救援，就如同人的左右手一样。
所以，想用缚住马缰、深埋车轮这种显示死战决心的办法来稳定部队，是靠不住的。
要使部队能够齐心协力奋勇作战如同一人，关键在于部队管理教育有方。
要使强弱不同的士卒都能发挥作用，在于恰当地利用地形。
所以善于用兵的人，能使全军上下携手团结如同一人，这是因为客观形势迫使部队不得不这样。
英文这么说：
The skillful tactician may be likened to the shuai-jan.
Now the shuai-jan is a snake that is found in the ChUng mountains.
Strike at its head, and you will be attacked by its tail;
strike at its tail, and you will be attacked by its head;
strike at its middle,and you will be attacked by head and tail both.
Asked if an army can be made to imitate the shuai-jan,I should answer, Yes.
For the men of Wu and the men of Yueh are enemies;
yet if they are crossing a river in the same boat and are caught by a storm,
they will come to each other's assistance just as the left hand helps the right.
Hence it is not enough to put one's trust in the tethering of horses, and the burying of chariot wheels inthe ground
The principle on which to manage an army is to set up one standard of courage which all must reach.
How to make the best of both strong and weak—that is a question involving the proper use of ground.
Thus the skillful general conducts his army just as though he were leading a single man, willy-nilly, by the hand.
单句理解：
孙子在这里谈到的仍然是军队的组织协调问题，他强调不要试图用一些外在的力量迫使部队稳定，而应当依靠有效的管理和教育给士卒以内的动力，以此规范和约束他们，从而使全军上下统一思想，步调一致。
