Syllable structure

The general structure of a syllable consists of the following segments:

* Onset (obligatory in some languages, optional or even restricted in others)
* Rhyme
o Nucleus (obligatory in all languages)
o Coda (optional in some languages, highly restricted or prohibited in others)

tree representation of a CVC syllable
tree representation of a CVC syllable

In some theories of phonology, these syllable structures are displayed as tree diagrams (similar to the trees found in some types of syntax).

The syllable nucleus is typically a sonorant, usually a vowel sound, in the form of a monophthong, diphthong, or triphthong, but sometimes sonorant consonants like [l] or [r]. The syllable onset is the sound or sounds occurring before the nucleus, and the syllable coda (literally 'tail') is the sound or sounds that follow the nucleus. The term rhyme covers the nucleus plus coda. In the one-syllable English word cat, the nucleus is a, the onset c, the coda t, and the rhyme at. This syllable can be abstracted as a consonant-vowel-consonant syllable, abbreviated CVC.

Generally, every syllable requires a nucleus. Onsets are extremely common, and some languages require all syllables to have an onset. (That is, a CVC syllable like cat is possible, but a VC syllable such as at is not.) A coda-less syllable of the form V, CV, CCV, etc. is called an open syllable, while a syllable that has a coda (VC, CVC, CVCC, etc.) is called a closed syllable (or checked syllable). All languages allow open syllables, but some, such as Hawaiian, do not have closed syllables.

A heavy syllable is one with a branching rhyme or a branching nucleus — this is a metaphor, based on the nucleus or coda having lines that branch in a tree diagram. In some languages, heavy syllables include both VV (branching nucleus) and VC (branching rhyme) syllables, contrasted with V, which is a light syllable. In other languages, only VV syllables (ones with a long vowel or diphthong) are heavy, while both VC and V syllables are light. The difference between heavy and light frequently determines which syllables receive stress—this is the case in Latin and Arabic, for example. In moraic theory, heavy syllables are said to have two moras, while light syllables are said to have one. Japanese is generally described this way.

In other languages, including English, a consonant may be analyzed as acting simultaneously as the coda of one syllable and the onset of the following syllable, a phenomenon known as ambisyllabicity. Examples occurring in Received Pronunciation include words such as arrow [ˈærəʊ], error [ˈerə], mirror [ˈmɪrə], borrow [ˈbɒrəʊ], burrow [ˈbʌrəʊ], which can't be divided into separately pronounceable syllables: neither [æ] nor [ær] is a possible independent syllable, and likewise with the other short vowels [e ɪ ɒ ʌ].