Most Chinese words are composed of two syllables. When a syllable begins with the vowel a, o, or e and is immediately followed by another syllable, a syllable-dividing mark (' ) should be used to separate them if the boundaries between the syllables might otherwise become unclear. This practice prevents misinterpretation of compound words.
☞ ku'ai (酷爱, ardently love) ←→ kuai (快, fast; quick)
☞ shang'e (上腭, palate) ←→ shange (山歌, folk songs)
☞ xi'an (西安, Xi'an city, Capital of Shaanxi Province) ←→ xian (先, earlier; before; first; in advance)
☞ dang'an (档案, files) ←→ dangan (单干, to go it alone)
Without the syllable-dividing mark, it can be difficult to determine where one syllable ends and another begins, especially when the second syllable starts with a vowel. This can lead to confusion in pronunciation and meaning.
For example:
Use the syllable-dividing mark (' ) when:
Note: The syllable-dividing mark is only used when necessary to avoid confusion. In most cases, syllable boundaries are clear from context and do not require the mark.