Sun Tzu on the Art of War: Energy
Sun Tzu said: The control of a large force is the same principle as the control of a few men: it is merely a question of dividing up their numbers. 
Fighting with a large army under your command is nowise different from fighting with a small one: it is merely a question of instituting signs and signals.
To ensure that your whole host may withstand the brunt of the enemy's attack and remain unshaken - this is effected by maneuvers direct and indirect. 
That the impact of your army may be like a grindstone dashed against an egg - this is effected by the science of weak points and strong.
In all fighting, the direct method may be used for joining battle, but indirect methods will be needed in order to secure victory. 
Indirect tactics, efficiently applied, are inexhausible as Heaven and Earth, unending as the flow of rivers and streams; like the sun and moon, they end but to begin anew; like the four seasons, they pass away to return once more. 
There are not more than five musical notes, yet the combinations of these five give rise to more melodies than can ever be heard.
There are not more than five primary colors (blue, yellow, red, white, and black), yet in combination they produce more hues than can ever been seen.
There are not more than five cardinal tastes (sour, acrid, salt, sweet, bitter), yet combinations of them yield more flavors than can ever be tasted.
In battle, there are not more than two methods of attack - the direct and the indirect; yet these two in combination give rise to an endless series of maneuvers.
The direct and the indirect lead on to each other in turn. It is like moving in a circle - you never come to an end. Who can exhaust the possibilities of their combination?
The onset of troops is like the rush of a torrent which will even roll stones along in its course.
The quality of decision is like the well-timed swoop of a falcon which enables it to strike and destroy its victim. 
Therefore the good fighter will be terrible in his onset, and prompt in his decision. 
Energy may be likened to the bending of a crossbow; decision, to the releasing of a trigger. 
Amid the turmoil and tumult of battle, there may be seeming disorder and yet no real disorder at all; amid confusion and chaos, your array may be without head or tail, yet it will be proof against defeat. 
Simulated disorder postulates perfect discipline, simulated fear postulates courage; simulated weakness postulates strength. 
Hiding order beneath the cloak of disorder is simply a question of subdivision;  concealing courage under a show of timidity presupposes a fund of latent energy;  masking strength with weakness is to be effected by tactical dispositions. 
Thus one who is skillful at keeping the enemy on the move maintains deceitful appearances, according to which the enemy will act.  He sacrifices something, that the enemy may snatch at it.
By holding out baits, he keeps him on the march; then with a body of picked men he lies in wait for him. 
The clever combatant looks to the effect of combined energy, and does not require too much from individuals.  Hence his ability to pick out the right men and utilize combined energy.
When he utilizes combined energy, his fighting men become as it were like unto rolling logs or stones. For it is the nature of a log or stone to remain motionless on level ground, and to move when on a slope; if four-cornered, to come to a standstill, but if round-shaped, to go rolling down. 
Thus the energy developed by good fighting men is as the momentum of a round stone rolled down a mountain thousands of feet in height. So much on the subject of energy. 
That is, cutting up the army into regiments, companies, etc., with subordinate officers in command of each. Tu Mu reminds us of Han Hsin's famous reply to the first Han Emperor, who once said to him: "How large an army do you think I could lead?" "Not more than 100,000 men, your Majesty." "And you?" asked the Emperor. "Oh!" he answered, "the more the better."
We now come to one of the most interesting parts of Sun Tzu's treatise, the discussion of the CHENG and the CH`I." As it is by no means easy to grasp the full significance of these two terms, or to render them consistently by good English equivalents; it may be as well to tabulate some of the commentators' remarks on the subject before proceeding further. Li Ch`uan: "Facing the enemy is CHENG, making lateral diversion is CH`I. Chia Lin: "In presence of the enemy, your troops should be arrayed in normal fashion, but in order to secure victory abnormal maneuvers must be employed." Mei Yao-ch`en: "CH`I is active, CHENG is passive; passivity means waiting for an opportunity, activity beings the victory itself." Ho Shih: "We must cause the enemy to regard our straightforward attack as one that is secretly designed, and vice versa; thus CHENG may also be CH`I, and CH`I may also be CHENG." He instances the famous exploit of Han Hsin, who when marching ostensibly against Lin- chin (now Chao-i in Shensi), suddenly threw a large force across the Yellow River in wooden tubs, utterly disconcerting his opponent. [Ch`ien Han Shu, ch. 3.] Here, we are told, the march on Lin-chin was CHENG, and the surprise maneuver was CH`I." Chang Yu gives the following summary of opinions on the words: "Military writers do not agree with regard to the meaning of CH`I and CHENG. Wei Liao Tzu [4th cent. B.C.] says: 'Direct warfare favors frontal attacks, indirect warfare attacks from the rear.' Ts`ao Kung says: 'Going straight out to join battle is a direct operation; appearing on the enemy's rear is an indirect maneuver.' Li Wei-kung [6th and 7th cent. A.D.] says: 'In war, to march straight ahead is CHENG; turning movements, on the other hand, are CH`I.' These writers simply regard CHENG as CHENG, and CH`I as CH`I; they do not note that the two are mutually interchangeable and run into each other like the two sides of a circle [see infra, ss. 11]. A comment on the T`ang Emperor T`ai Tsung goes to the root of the matter: 'A CH`I maneuver may be CHENG, if we make the enemy look upon it as CHENG; then our real attack will be CH`I, and vice versa. The whole secret lies in confusing the enemy, so that he cannot fathom our real intent.'" To put it perhaps a little more clearly: any attack or other operation is CHENG, on which the enemy has had his attention fixed; whereas that is CH`I," which takes him by surprise or comes from an unexpected quarter. If the enemy perceives a movement which is meant to be CH`I," it immediately becomes CHENG."
Chang Yu says: "Steadily develop indirect tactics, either by pounding the enemy's flanks or falling on his rear." A brilliant example of "indirect tactics" which decided the fortunes of a campaign was Lord Roberts' night march round the Peiwar Kotal in the second Afghan war. ["Forty-one Years in India," chapter 46.]
Tu Yu and Chang Yu understand this of the permutations of CH`I and CHENG." But at present Sun Tzu is not speaking of CHENG at all, unless, indeed, we suppose with Cheng Yu-hsien that a clause relating to it has fallen out of the text. Of course, as has already been pointed out, the two are so inextricably interwoven in all military operations, that they cannot really be considered apart. Here we simply have an expression, in figurative language, of the almost infinite resource of a great leader.
The Chinese here is tricky and a certain key word in the context it is used defies the best efforts of the translator. Tu Mu defines this word as "the measurement or estimation of distance." But this meaning does not quite fit the illustrative simile in ss. 15. Applying this definition to the falcon, it seems to me to denote that instinct of SELF RESTRAINT which keeps the bird from swooping on its quarry until the right moment, together with the power of judging when the right moment has arrived. The analogous quality in soldiers is the highly important one of being able to reserve their fire until the very instant at which it will be most effective. When the "Victory" went into action at Trafalgar at hardly more than drifting pace, she was for several minutes exposed to a storm of shot and shell before replying with a single gun. Nelson coolly waited until he was within close range, when the broadside he brought to bear worked fearful havoc on the enemy's nearest ships.
The word "decision" would have reference to the measurement of distance mentioned above, letting the enemy get near before striking. But I cannot help thinking that Sun Tzu meant to use the word in a figurative sense comparable to our own idiom "short and sharp." Cf. Wang Hsi's note, which after describing the falcon's mode of attack, proceeds: "This is just how the 'psychological moment' should be seized in war."
None of the commentators seem to grasp the real point of the simile of energy and the force stored up in the bent cross- bow until released by the finger on the trigger.
Mei Yao-ch`en says: "The subdivisions of the army having been previously fixed, and the various signals agreed upon, the separating and joining, the dispersing and collecting which will take place in the course of a battle, may give the appearance of disorder when no real disorder is possible. Your formation may be without head or tail, your dispositions all topsy-turvy, and yet a rout of your forces quite out of the question."
In order to make the translation intelligible, it is necessary to tone down the sharply paradoxical form of the original. Ts`ao Kung throws out a hint of the meaning in his brief note: "These things all serve to destroy formation and conceal one's condition." But Tu Mu is the first to put it quite plainly: "If you wish to feign confusion in order to lure the enemy on, you must first have perfect discipline; if you wish to display timidity in order to entrap the enemy, you must have extreme courage; if you wish to parade your weakness in order to make the enemy over-confident, you must have exceeding strength."
See supra, ss. 1.
The commentators strongly understand a certain Chinese word here differently than anywhere else in this chapter. Thus Tu Mu says: "seeing that we are favorably circumstanced and yet make no move, the enemy will believe that we are really afraid."
Chang Yu relates the following anecdote of Kao Tsu, the first Han Emperor: "Wishing to crush the Hsiung-nu, he sent out spies to report on their condition. But the Hsiung-nu, forewarned, carefully concealed all their able-bodied men and well-fed horses, and only allowed infirm soldiers and emaciated cattle to be seen. The result was that spies one and all recommended the Emperor to deliver his attack. Lou Ching alone opposed them, saying: "When two countries go to war, they are naturally inclined to make an ostentatious display of their strength. Yet our spies have seen nothing but old age and infirmity. This is surely some ruse on the part of the enemy, and it would be unwise for us to attack." The Emperor, however, disregarding this advice, fell into the trap and found himself surrounded at Po-teng."
Ts`ao Kung's note is "Make a display of weakness and want." Tu Mu says: "If our force happens to be superior to the enemy's, weakness may be simulated in order to lure him on; but if inferior, he must be led to believe that we are strong, in order that he may keep off. In fact, all the enemy's movements should be determined by the signs that we choose to give him." Note the following anecdote of Sun Pin, a descendent of Sun Wu: In 341 B.C., the Ch`i State being at war with Wei, sent T`ien Chi and Sun Pin against the general P`ang Chuan, who happened to be a deadly personal enemy of the later. Sun Pin said: "The Ch`i State has a reputation for cowardice, and therefore our adversary despises us. Let us turn this circumstance to account." Accordingly, when the army had crossed the border into Wei territory, he gave orders to show 100,000 fires on the first night, 50,000 on the next, and the night after only 20,000. P`ang Chuan pursued them hotly, saying to himself: "I knew these men of Ch`i were cowards: their numbers have already fallen away by more than half." In his retreat, Sun Pin came to a narrow defile, with he calculated that his pursuers would reach after dark. Here he had a tree stripped of its bark, and inscribed upon it the words: "Under this tree shall P`ang Chuan die." Then, as night began to fall, he placed a strong body of archers in ambush near by, with orders to shoot directly they saw a light. Later on, P`ang Chuan arrived at the spot, and noticing the tree, struck a light in order to read what was written on it. His body was immediately riddled by a volley of arrows, and his whole army thrown into confusion. [The above is Tu Mu's version of the story; the SHIH CHI, less dramatically but probably with more historical truth, makes P`ang Chuan cut his own throat with an exclamation of despair, after the rout of his army.]
With an emendation suggested by Li Ching, this then reads, "He lies in wait with the main body of his troops."
Tu Mu says: "He first of all considers the power of his army in the bulk; afterwards he takes individual talent into account, and uses each men according to his capabilities. He does not demand perfection from the untalented."
Ts`au Kung calls this "the use of natural or inherent power."
The chief lesson of this chapter, in Tu Mu's opinion, is the paramount importance in war of rapid evolutions and sudden rushes. "Great results," he adds, "can thus be achieved with small forces."