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 manœuver.’ 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, § 11]. A comment on the T’ang Emperor T’ai Tsung goes to the root of the matter: ‘A _ch’i_ manœuver 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_."] 4. 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. 5. In all fighting, the direct method may be used for joining battle, but indirect methods will be needed in order to secure victory. [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. [1] 6. 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 but to return once more. [Tu Yu and Chang Yu understand this of the permutations of _ch’i_ and _cheng_. But at present Sun Tzŭ 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.] 7. There are not more than five musical notes, yet the combinations of these five give rise to more melodies than can ever be heard. 8. There are not more than five primary colours (blue, yellow, red, white, and black), yet in combination they produce more hues than can ever be seen. 9 There are not more than five cardinal tastes (sour, acrid, salt, sweet, bitter), yet combinations of them yield more flavours than can ever be tasted.