Vietnamese is a tonal language, i.e. the meaning of each word depends on the “tone” (basically a specific tone and glottalization pattern) in which it is pronounced. There are six distinct tones in the standard Northern dialect. In the south, there is a merging of the hỏi and ngã tones, in effect leaving five basic tones. The first one (“level tone”) is not marked, and the other five are indicated by diacritics applied to the vowel part of the syllable. The tone names are chosen such that the name of each tone is spoken in the tone it identifies.
|Ngang or Bằng||mid level, ˧||unmarked|
|Huyền||low falling, ˨˩||grave accent|
|Ngã||glottalized rising, ˧˥ˀ||tilde|
|Sắc||high rising, ˧˥||acute accent|
|Nặng||glottalized falling, ˧˨ˀ||dot below|
- Unmarked vowels are pronounced with a level voice, in the middle of the speaking range.
- The grave accent indicates that the speaker should start somewhat low and drop slightly in tone, with the voice becoming increasingly breathy.
- The hook indicates that the speaker should start somewhat low, and fall, then rise, as in a question.
- A tilde indicates that the speaker should start mid, break off (with a glottal stop), then start again and rise like a question in tone.
- The acute accent indicates that the speaker should start mid and rise sharply in tone.
- The dot signifies that the speaker should start low and fall lower in tone, with the voice becoming increasingly creaky and ending in a glottal stop.
In syllables where the vowel part consists of more than one vowel (such as diphthongs and triphthongs), the placement of the tone is still a matter of debate. Generally, there are two methodologies, an “old style” and a “new style”. While the “old style” emphasizes aesthetics by placing the tone mark as close as possible to the center of the word (by placing the tone mark on the last vowel if an ending consonant part exists and on the next-to-last vowel if the ending consonant doesn’t exist, as in hóa), the “new style” emphasizes linguistic principles and tries to apply the tone mark on the main vowel (as in hoá). In both styles, when one vowel already has a quality diacritic on it, the tone mark must be applied to it as well, regardless of where it appears in the syllable (thus thuế is acceptable while thúê is not). In the case of the ươ diphthong, the mark is placed on the ơ. The u in qu is considered part of the consonant. Currently, the new style is usually used in new documents, while some people still prefer the old style.
In lexical ordering, differences in letters are treated as primary, differences in tone markings as secondary, and differences in case as tertiary differences. Ordering according to primary and secondary differences proceeds syllable by syllable. According to this principle, a dictionary lists tuân thủ before tuần chay because the secondary difference in the first syllable takes precedence over the primary difference in the second.
The signs always go on the vowels. If there are many vowels in a word, the sign will go on the last vowel, unless that vowel ends the word. For example: tuần (meaning “week”), thưởng (meaning “reward”), tuyết (meaning “snow”), yếu (meaning “weak”), etc.
As a result of influence from the Chinese writing system, each syllable in Vietnamese is written separately as if it were a word. In the past, syllables in multisyllabic words were concatenated with hyphens, but this practice had died out, and hyphenation is now reserved for foreign borrowings. A written syllable consists of at most three parts, in the following order from left to right:
- An optional beginning consonant part
- A required vowel syllable nucleus and the tone mark, if needed, applied above or below it
- An optional ending consonant part, can only be one of the following: c, ch, m, n, ng, nh, p, t, or nothing.