In phonetics and phonology, a syllable onset is the part of a syllable that precedes the syllable nucleus. In the study of Chinese languages, onsets are better known as initials or in Chinese, shengmu (PY: shēngmǔ, TC: 聲母, SC: 声母).

Syllable structure

The segmental structure of a syllable begins with an optional onset, followed by a compulsory rime or final (yunmu).

syllable: C₁(C₂)V₁(V₂)(C₃)(C₄) = onset: C₁(C₂) + rime: V₁(V₂)(C₃)(C₄)

syllable: V₁(V₂)(C₃)(C₄) = onset: Ø (null) + rime: V₁(V₂)(C₃)(C₄)

(C = consonant, V = vowel, optional components are in parentheses.)

Depending on the phonotactics of a language, the onset can consist of a single consonant or a consonant cluster. If a syllable begins with a vowel or another syllabic sonorant, then the syllable is said to have no onset, or a null onset. In Chinese language studies, the terms null initial and zero initial are used as well.

Chinese language studies

The onset or initial was first called shēngniǔ (TC: 聲紐, SC: 声纽), or simply shēng or niǔ, in traditional phonological studies since the Jìn Dynasty. For each group of characters pronounced with the same initial consonant, one was picked to name the initial. One character was also picked from the group without an initial consonant, which was the beginning of the concept of the null initial.