These are the words of Master Sun:
When the state is at war, the commander will receive his orders from the sovereign of the state. The first task is to mobilize the army and have it set up camp. Not until this task has been completed can the commander set about making the army a harmonious whole.
Then comes the task of tactical maneuvering, and there is no more difficult task than this. Tactical maneuvering is difficult because the commander must make winding roads into straight ones and misfortune into good fortune.
The mark of a tactically talented commander is his ability to fool the enemy into taking detours, to march his own army across difficult terrain as part of a long and complicated route and reach the objective before the enemy -- despite the enemy having a head start.
It can be useful to put the army in motion, but it also entails certain dangers.
If you send your entire army on the road to gain an advantage, chances are you will arrive too late, as the entirety of an army moves slowly. But if you detach only the troops who can make great haste, you will be sacrificing your wagon train of supplies. If you, in the pursuit of an advantage, command your troops to roll up their sleeves and force their pace such that they travel day and night with no rest, they will travel twice the normal distance an army can travel -- and end up captured by the enemy.
The strongest soldiers will find themselves at the front of an army on the move, while the weak and unhappy will lag behind. You can lose a tenth of your army in this way before you reach your objective. If you march sixteen miles [fifty li] to outmaneuver the enemy, you will lose the leader of the vanguard, and only half your army will arrive. If you march nine miles [thirty li] to reach the same objective, you will lose one-third of your army. Also note that an army without its wagon train of supplies is doomed; the same is true of an army without provisions and an army with no supply base.
We cannot make alliances until we have gotten to know the intentions of our neighbors. We cannot put our army into motion until we know the terrain - the mountains and the forests, the valleys and the gorges, the swamps and the marshes. We cannot use the terrain to our advantage if we do not employ local people as scouts.
Keep the enemy ignorant about your strength and you will achieve victory.
Let circumstances determine whether you should gather your troops together or divide them. Move like the wind and be as impenetrable as a dense forest. Rage like fire and be unyielding like a mountain.
Keep your plans hidden in darkness and strike like lightning from a clear sky. Let your men share in the loot when you plunder a province, and divide conquered territory among your troops.
Weigh your plans carefully and discuss them before you set them into motion.
He who knows how to operate outside of the established rules will find victory for himself. This is the art of maneuvering.
The Book of Military Management [presumably a military treatise of Sun Tzu's time, now lost] states the following: "In battle your voice cannot carry far; we therefore use gongs and drums for signaling. The troops cannot see each other clearly at a distance; we therefore use flags and banners."
Gongs and drums, banners and flags are the tools through which you focus the attention of the army. If the army is made into a single entity, the brave cannot advance on their own, and the cowards cannot retreat on their own. This is the art of leading a great host of people. Use torches and drums when fighting at night, and flags and banners during the day, to affect both your own troops and the troops of the enemy. An entire army can lose its courage and a commander can lose his composure [if you use flags and banners to great effect against the enemy].
A soldier is keenest in the morning, but around noon his keenness begins to leave him, and by nighttime he longs to return to camp.
A wise commander avoids an enemy army keen on battle. He waits until the enemy has grown sluggish and has begun longing for his camp. By surveying moods you can control army morale. It is a difficult task to keep up the morale of your army while you wait in a disciplined manner for disorder and confusion to grasp the enemy.
To be near your objective while the enemy is still far away, to wait comfortably while your enemy is toiling, to have a surplus of supplies while the enemy lacks necessities - this is the art of prudence.
Not to engage an enemy who is calm and confident, with banners arrayed in perfect order - this is the art of observing circumstances.
Never attack an enemy uphill, and do not engage him if he attacks you from the high ground.
Do not pursue an army that only pretends to be routed. Do not attack soldiers who are keen on doing battle. Do not let the enemy bait you.
Do not engage an army that is returning home. When you encircle an enemy force, you should always leave an avenue of escape open. Do not pressure a desperate enemy.
This is the art of war.