Vowel

A vowel is a speech sound produced with the vocal tract relatively open, allowing the air to flow through without significant constriction. Vowels are typically voiced and often form the core, or nucleus, of syllables in most languages.

Articulation of vowels depends on tongue and lip position. The height of the tongue (high, mid, low), the frontness or backness of the tongue, and whether the lips are rounded or unrounded combine to create distinct vowel qualities. Vowels can be tense or lax, and in many languages vowel length can contrast meaning, though this is not universal.

Vowel systems vary widely across languages. Some languages have a small inventory of vowels, others many more. The distinction between phonemic vowels, which differentiate words, and allophonic variation is central in phonology. Vowels may be monophthongs—pure steady-state sounds—or diphthongs, which involve a transition from one vowel quality to another within the same syllable.

In addition to standing alone, vowels participate in a range of processes. Vowel harmony, rounding harmony, nasalization, and vowel reduction are common in different language families. Written systems usually represent vowels with letters or diacritics, though some languages employ orthographies with limited explicit vowel length or use diacritics to mark features such as tone or nasalization.

Acoustically, vowel quality is related to resonant frequencies of the vocal tract; vowel height and backness influence the first and second formant frequencies. Vowels are a fundamental component of phonetics and phonology, shaping syllable structure and distinguishing meanings across languages.