These are the words of Master Sun:
The art of war is a matter of grave importance to the state. To master the waging of war is, in fact, a question of life and death, as war will bring about either security or destruction for the state. Sovereigns should therefore take great care when they study the art of war.
The art of war can be divided into five principles any sovereign needs to assess before plunging his state into war:
Harmony represents the degree of concordance that exists between a sovereign and his people. If a sovereign is in harmony with his people, they will have the same goals he has, and the people will thus follow their sovereign into battle with no regard for the mortal dangers of war.
Heaven represents day and night, warmth and cold, time and season.
Earth represents distances, open terrain and narrow passes, the large and the small, and the variability of life and death.
The Commander represents the virtues of wisdom: courage, geniality, severity, and rigor.
Discipline represents the structuring of the army into suitable units, the hierarchy of the officers, the managing of logistics, and the management of expenses.
All leaders should be conscious of these five principles of war. Those who know them will emerge victorious, and those who remain ignorant of these five principles of war will perish on the battlefield.
If you need to gauge the relative strength of two armies, you need to let yourself be guided by the following seven comparisons:
Using just these seven comparisons, I [Sun Tzu] can predict who will be the victor and who will be vanquished.
The commander who listens to my advice and acts according to it will win battles. Therefore let such a commander keep the mantle of command. The commander who does not listen to my advice - or who fails to act in accordance with it - will lose battles. Such a commander should be stripped of his command.
While you take advantage of my advice, you should also be mindful of circumstances beyond my general advice that might be useful to your cause. You should always change your plans according to the circumstances at hand.
All war is based on deception.
When we are capable of attacking, we must therefore pretend not to be able to move.
When we send our troops into action, the enemy must be made to think that we are at rest. When we are near, the enemy must be made to think that we are far away. This is true also in reverse. You need to lure the enemy into delusion. Create chaos in his mind and crush him with force.
If the enemy is secure in his position, you need to be ready for battle. If the enemy has achieved supremacy, you need to avoid him on the battlefield.
If the enemy is hot-tempered, irritate him. Pretend that you are weak, and he will perhaps overcommit. If the enemy takes his time and seeks ease, then make it so that he cannot rest. If the enemy's forces are united, then separate them. Attack him where he is unprepared; appear where he least expects you.
These methods, which will lead a commander to victory, cannot be discussed theoretically and in advance divorced from the specifics of the battle at hand.
The commander who wins battles spends many hours in a quiet place studying all these factors I have discussed here. The commander who loses makes little time for studying any of the factors I have outlined here. Careful planning thus brings victory, while half-hearted planning brings about defeat. No planning at all will bring nothing but certain and utter destruction.
By observing just this aspect of a commander [his willingness to study before the battle], I can predict who is likely to emerge victorious on the battlefield and who is likely to find only defeat on the battlefield.