Four corner method

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The four corner method (literal translation), (Traditional Chinese: 四角號碼檢字法, Simplified Chinese: 四角号码检字法, pinyin: sì jiǎo hào mǎ jiǎn zì fǎ), much more commonly called the "Four Corner System", the English term preferred by the inventor and used by most English speakers and writers, is a method of encoding Chinese characters using four numerical digits per character (in many if not most situations, especially in large indexes and encyclopedias, an additional digit is used).

The method was invented by Wang Yunwu (王云五), the Editor-in-chief of the Commercial Press Ltd., China, in the 1920s. He developed it based on earlier efforts, chiefly by the Russian scholar Rosenberg in the 19th Century, and experiments by Lin Yutang and others. His original purpose, as he wrote in an introductory pamphlet of 1926 called simply Sijiaohaoma Jianzifa, (Commercial Press, Shanghai) had been to aid telegraphers in looking up CST, China Standard Telecode numbers then in use, from long lists of characters. Cai Yuanpei (Ts'ai Yuan-p'ei) and Hu Shi (Hu Shih) wrote introductory essays for this booklet, and Hu famously composed a poem as a "memory key" to the system, his then-famous "Bihuahaoma Ge" (筆畫號碼歌):

一橫二垂三點捺，
點下帶橫變零頭，
叉四插五方塊六，
七角八八小是九。

一横二垂三点捺，
点下带横变零头，
叉四插五方块六，
七角八八小是九。

Yi heng, er chui, san dian, na;
Dian xia dai heng, bian ling tou;
Cha si, cha wu, fang kuai liu;
Qi jiao, ba ba, xiao shi jiu.

In the 1950s, lexicographers in the Peoples Republic changed the poem somewhat to avoid association with the (then) unmentionable Hu Shi (see the new version, with characters, below).

The first revised version was published in Shanghai in 1928. It was quickly adopted and popularized as a method of arranging and indexing Chinese characters in dictionaries, and as an indexing system for Chinese classical and modern books, as well as for library indexing and hospital and police records, Chinese typewriters, military code making (handling the characters quickly) and so forth. The Wang Yun-wu Da Cidian (Wang Yun-wu Ta Tz'u-tien) of 1928 was a remarkable work for its time, but the lack of a phonetic index diminished its overall usefulness (although the pronunciations were very much in line with today's putonghua), and the northern Mandarin pronunciations were given in the then-new "Guoyu Luomazi" devised by linguist Zhao Yuanren as well as in MPS characters with a dotted corner for tone. It also delineated parts of speech, and all compounds were listed by the four-corner method as well. It was extremely modern. It used some arcane styles of characters as a citation form, and had a few errors and some important omissions.

The famed lexicographer and "Ci Yuan" (T'zu Yuan) author Lu Erkui (Lu Er-k'ui) and other lexicographers became early proponents, and by 1931 the Commercial Press had indexed virtually all the classical reference works and collections of China (such as the Pei Wen Yun Fu and Si Ku Quan Shu as well as many modern ones by the four-corner method. Hospital, personnel and police records were organized just like the biographical indexes and dynastic histories of former times; it seemed for awhile (Nash, Trindex, 1930) that the four-corner method was on its way to replacing the Kang Xi Bushou (K'ang-hsi Pu-shou) 214 Radical System left by the Qing (Ch'ing) Dynasty. Internationally, Harvard and other universities were using the method for their book collections, and the KMT Nanjing Government seemed to have selected this numerical system as its standard. It was taught in primary schools to children in Shanghai and other locations during the late 1920s and throughout the 30s up to the outbreak of general war with Japan in 1937.

The Japanese militarists found this publishing activity and popularity of sijiaohaoma and its academic, administrative and military uses threatening enough for them to actually destroy the Commercial Press building, shelling and burning it during the January 1932 Shanghai Incident. Books produced afterward from damaged plates did not have such clarity and were marked "Guo Nan Hou Ban" (kuo-nan hou-pan) on the page margins. Sijiaohaoma was a way that China, without a unified spoken language as yet, could draw upon the strength of its unified WRITTEN language, old and new. Anything that helped unify China was anathema to the Japanese then.

The four-corner method was extremely popular in government education circles until pronunciation based systems using the Mandarin Phonetic Symbols (the Guoyu Luomazi thought to be too radical and difficult) in the GR phonetic chart's (labial-to-velar) "bo-po-mo-fo" order became fashionable in the mid 1930s, to promote spoken language unification. The first such large scale project was Wang Li's 4 volume MPS-entry Guoyu Cidian (Kuo-yu Tz'u-tien) of 1936, and in 1949 it was re-edited into the all MPS Hanyu Cidian with Kang Xi 214 radical index, and a small 4-Corner Dictionary was available as the Xin Sijiaohaoma Cidian of c1953. Limited use of MPS and the original four corner system continued under the People's Government after 1949 until the introduction of pinyin in 1958 (below) and after. MPS characters still remain in today's Chinese dictionaries below each Pinyin class entry and sometimes in a phonetics chart in tables (Xinhua Cidian), while main entries are all in Hanyu Pinyin order. There is one all-sijiaohaoma small dictionary, (Third Revision, below).

A minor Second Revision was made during and just after WWII, and this was used by most postwar lexicographers including Morohashi Testsuji, who created his 12-volume Dai Kanwa Jiten (Sino-Japanese Dictionary) with it and included the four-corner index among several other lookup methods. Olshanin (USSR)included a four-corner index in his Chinese -Russian Dictionary and in new China, an extraordinary project of the 25 Histories (Ershi wu shi) was published in the early 1950s with a four corner index volume to the entire contents. Then, in 1958, with the introduction of Pinyin, a small "Xin Sijiaohaoma Cidian" was produced by the Beijing Commercial Press but the rapid Han character simplification of the following years made the small (30,000 compound) book obsolete in China. It remained popular overseas and in Hong Kong for a number of years as a high speed key to phonetic dictionaries and indexes, by those partly literate in Chinese or those in some areas who were unfamiliar with Putonghua, let alone Hanyu Pinyin. Wang Yunwu produced a "Xiao Cidian" and "Zonghe Cidian" in the late 1940s and the later remains in print in Taiwan with an auxiliary section of rare characters, with telecode number and radical and stroke count shown for each character, and a convenient size, but it still lacks a phonetic index and is all traditional Chinese with much obsolete information; convenient for reading old Republic period materials and literature and as a handy finder for pronunciations.

During the Great Proletarian Cultural Revolution, the Four Corner System underwent a radical Third Revision during the compilation of the experimental volume of the Xiandai Hanyu Cidian, Commercial Press, Beijing, 1972. Another medium sized dictionary, the Xinhua Cidian, appeared with this index as well, but in the late 1990s the four corner index disappeared from newer editions. Both works now use use only the Pinyin main entry and multi-door radical index systems that make it possible to look up a character with perhaps a wrong radical (ie, characters appear redundantly under different radicals) and the number of strokes and variant forms are greatly reduced, and many more people are literate and capable of transcribing standard Chinese with Pinyin. The use of stroke counting and radicals puts memorization of the character ahead of sheer speed in handling it (utility). This method is more supportive of mass literacy, a more important priority than classical scholarship or processing and filing names or characters for the majority in China today. The four-corner method is ultimately for readers, researchers, editors and fileclerks, not for writers who seek a character that they know in speech or recitation. In China today, a new version of the excellent small "Xin Sijiaohaoma Cidian, soft cover from from Commercial Press, Beijing, has been available since the late 1970s, updated in several new editions and printings. It uses the Third Revision (above) and enjoys some popularity.

A new alpha-numerical shape system called Wubi, "Five Brushes", one of several such new systems generating one discreet number for each character, is being promoted by the People's Government today for computer use. I recently personally observed Chinese hospital clerks and some members of the general public fairly skillful at this input method.

The main purpose of the original four-corner system today is in doing academic research or handling large numbers of characters or terms, index cards, names etc, quickly, as opposed to browsing long lists, and in computer entry, where a smaller list is created to browse from than with other systems. Many beginning users find the rules for the fifth number in all three revisions to be a bit contrary; it is like language itself, a bit chaotic but one becomes fluent in it. The Xinhua Zidian large type edition is available with a four corner index for those whose failing eyesight precludes browsing and counting strokes.

In China today, many famous KMT period reference books and collections with four corner indexes are being reprinted for sale to scholars and those interested in Old Chinese language, historical studies etc.

The four digits used to encode each character are chosen according to the "shape" of the four corners of each character, i.e. the upper left, upper right, lower left and lower right corners. The shapes can be memorized using a Chinese poem; this version, from the 1958 Xin Sijiaohaoma Cidian, is reworded to avoid the stigma (at that time) of Hu Shi's original poem, (above). The 1950s version is as follows:

横一垂二三點捺，
叉四插五方框六，
七角八八九是小，
點下有横變零頭。

横一垂二三点捺，
叉四插五方框六，
七角八八九是小，
点下有横变零头。

Heng yi, chui er, san dian, na;
Cha si, cha wu, fang kuang liu;
Qi jiao, ba ba, jiu shi xiao;
Dian xia you heng, bian ling tou.

In short, the number 1 represents a horizontal stroke, 2 represents a vertical or diagonal stroke, 3 a dot stroke, 4 two strokes in a cross shape, 5 three or more strokes in which one stroke intersects all others, 6 a box-shape, 7 where a stroke turns a corner, 8 the shape of the Chinese character 八 and its inverted form, and 9 is used for the shape of the Chinese character 小 and its inverted form. Zero is used where there is either nothing in a corner, the part in a corner is already represented by a previous corner, or where a corner has a dot stroke followed by a horizontal stroke.

Several other notes:

A single stroke can be represented in more than one corner, as is the case with many curly strokes. (eg. the code for 乙 is 1771)
If the character is fenced by 囗, 門(门), or 鬥, the lower corners are used to denote what is inside the radical, instead of 00 for 囗 or 22 for the others. (eg. the code for 回 is 6060)

There have been scores, maybe hundreds, of such numerical and alpha-numerical (such as Lin Yutang's "Instant Index", Trindex, Head-tail, Wang An's Sanjiahaoma, Halpern etc) systems proposed or popularized; some Chinese refer to these generically as "sijiaohaoma" though this is not correct.

The Four-Corner Method or system, in its three revisions, is the one that was most widespread and actually supported by the Chinese state for a while, and is found in numerous older reference works (and some, like the Morohasi Daikanwa, and Kou Kanwa, Taishukan, Tokyo, and the Dictionaire Francaise de le Langue Chinoise, (Insitute Ricci, Taibei) still in publication) The later uses the First revision of 1928. The small Kangorin Sino-Japanese Dictionary by Yoneyama et al, Taishukan, Tokyo, had a four-corner index when it was introduced in the 1980s, but it has been since deleted. The four corner method is not in common usage in China today, including Taiwan, although dictionaries with it (above) are available in many bookshops and libraries for those who need or desire to learn or use it. It is identified, in public opinion, with the time when many Chinese were illiterate and the language was not yet unified; more Chinese today use the dictionary to help them write, not read. But it is useful for scholars, clerks, editors, compilers, and especially for foreigners who read Chinese. In recent years it has achieved a new usage as a character input system for computers, generating very short lists to browse.