enemy’s attack and remain unshaken—this is effected by manœuvers direct and indirect. [We now come to one of the most interesting parts of Sun Tzŭ’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 manœuvers must be employed." Mei Yao-ch’en: "_Ch’i_ is active, _cheng_ is passive; passivity means waiting for an opportunity, activity brings 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 manœuver 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 Tzŭ [4th cent. B.C.] says: ‘Direct warfare favours 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_."]