The skillful warriors in ancient times first made themselves invincible and then awaited the enemy's moment of vulnerability. Invincibility depends on oneself, but the enemy' vulnerability on himself. It follows that those skilled in war can make themselves invincible but cannot cause an enemy to be certainly vulnerable. Therefore, it can be said that, one may know how to win, but cannot necessarily do so.

Defend yourself when you cannot defeat the enemy, and attack the enemy when you can. One defends when his strangth is inadequate; he attacks when it is abundant. Those who are skilled in defense hide themselves as under the nine-fold earth; those in attack flash forth as from above the ninefold heavens. Thus, they are capable both of protecting themselves and of gaining a complete victory.

To foresee a victory which the ordinary man can foresee is not the acme of excellence. Neither is it if you triumph in battle and are universally acclaimed "expert," for to lift an autumn down requires no great strength, to distinguish between the sun and moon is no test of vision, to hear the thunderclap is no indication of acute hearing. In ancient times, those called skilled in war conquered an enemy easily conquered. And, therefore, the victories won by a master of war gain him neither reputation for wisdom nor merit for courage. For he wins his victories without erring. Without erring he establishes the certainty of his victory; he conquers an enemy already defeated. Therefore, the skillful commander takes up a position in which he cannot be defeated and misses no opportunity to overcome him enemy. Thus, a victorious army always seeks battle after his plans indicate that victory is possible under them, whereas an army destined to defeat fights in the hope of winning but without any planning. Those skilled in war cultivate their policies and strictly adhere to the laws and regulations. Thus, it is in their power to control success.

Now, the elements of the art of war are first, the measurement of space; second, the estimation of quantities; third, calculations; fourth, comparisons; and fifth, chances of victory. Measurements of space are derived from the ground. Quantities, comparisons from figures, and victory from comparisons. Thus, a victorious army is as one yi balanced against a grain, and a defeated army is as a grain balanced against one yi.