Written Chinese
Because the majority of modern Chinese words contain more than one character, there are at least two measuring sticks for Chinese literacy: the number of characters known, and the number of words known. John DeFrancis, in the introduction to his "Advanced Chinese Reader", estimates that a typical Chinese college graduate recognizes 4,000 to 5,000 characters, and 40,000 to 60,000 words. Jerry Norman, in "Chinese", places the number of characters somewhat lower, at 3,000 to 4,000. These counts are complicated by the tangled development of Chinese characters. In many cases, a single character came to be written in multiple ways. This development was restrained to an extent by the standardization of the seal script during the Qin dynasty, but soon started again. Although the "Shuowen Jiezi" lists 10,516 characters—9,353 of them unique (some of which may already have been out of use by the time it was compiled) plus 1,163 graphic variants—the "Jiyun" of the Northern Song Dynasty, compiled less than a thousand years later in 1039, contains 53,525 characters, most of them graphic variants.
Xu Shen
In the postface, Xu gives a brief account of the history of writing. According to legend, Chinese characters were first invented by Cang Jie, who was inspired by footprints to create a system of signs that refer to the natural world. These original graphs could then be combined to make meaningful characters with referents distinct from their component graphs. This was important for Xu Shen, who emphasized the productivity, even fertility, of Chinese writing. Despite the novel meanings of compound characters, Xu Shen believed that true understanding of composite characters was contingent on an understanding of their components. Providing clear explanation of these relationships lay at the heart of his motivation.
Central to Xu Shen's thought is the contrast between "wen" (文 patterns) and "zi" (字 characters), indeed these contrasting categories of graphs receive separate mention in the work's title. Even today, there is disagreement over the exact definitions of the two terms. The Song dynasty scholar Zheng Qiao (郑樵) first presented the interpretation that "wen" and "zi" are the difference between non-compound and compound characters. More recently, other scholars, such as Françoise Bottéro (2002), have argued that the addition of a specifically phonetic element (and thus not simply compounding) marks the principal difference between "wen" and "zi". From this original binary contrast, Xu Shen formally delineated for the first time the six categories (六书) of Chinese characters.
To organize the thousands of headwords, Xu Shen established 540 radicals, and ordered them from least to greatest complexity. Each radical then headed its own group, which in turn subsumed all composite characters which incorporated the specific radical. The total number of 540 has a cosmological weight, as it can be derived from the product of 6, 9, and 10. 6 and 9 are the numbers of Yin and Yang, and 10 a number signifying completion. This number symbolizes the exhaustive scope of the dictionary.