CJK characters
Chinese is written almost exclusively in Chinese characters. It requires over 3,000 characters for general literacy, but up to 40,000 characters for reasonably complete coverage. Japanese uses fewer characters — general literacy in Japanese can be expected with 1,945 characters. The use of Chinese characters in Korea is becoming increasingly rare, although idiosyncratic use of Chinese characters in proper names requires knowledge (and therefore availability) of many more characters. However, even today, students in South Korea are taught 1,800 characters.
Classical Chinese grammar
Compared to the written vernacular Chinese of today, the most notable difference is that Classical Chinese rarely uses words composed of two Chinese characters; nearly all words are written with one character only. This stands directly in contrast with vernacular Chinese, in which two-character words are extremely common. This phenomenon exists, in part, because as sound changes created homophones among words, compounding was used to resolve ambiguities.