In Old Chinese, (e.g. Classical Chinese) most words were monosyllabic and there was a close correspondence between characters and words. In modern Chinese (esp. Mandarin Chinese), characters do not necessarily correspond to words; indeed the majority of Chinese words today consist of two or more characters due to the merging and loss of sounds in the Chinese language over time. Rather, a character almost always corresponds to a single syllable that is also a morpheme. However, there are a few exceptions to this general correspondence, including bisyllabic morphemes (written with two characters), bimorphemic syllables (written with two characters) and cases where a single character represents a polysyllabic word or phrase.

What are most words in Old Chinese?