Most syllables have an onset. Some languages restrict onsets to be only a single consonant, while others allow multiconsonant onsets according to various rules. For example, in English, onsets such as pr-, pl- and tr- are possible but tl- is not, and sk- is possible but ks- is not. In Greek, however, both ks- and tl- are possible onsets, while contrarily in Classical Arabic no multiconsonant onsets are allowed at all.
Some languages require all syllables to have an onset; in these languages a null onset such as in the English word "at" is not possible. This is less strange than it may appear at first, as most such languages allow syllables to begin with a phonemic glottal stop (the sound in the middle of English "uh-oh", represented in the IPA as /ʔ/). Furthermore, in English and most other languages, a word that begins with a vowel is automatically pronounced with an initial glottal stop when following a pause, whether or not a glottal stop occurs as a phoneme in the language. Consequently, few languages make a phonemic distinction between a word beginning with a vowel and a word beginning with a glottal stop followed by a vowel, since the distinction will generally only be audible following another word. (However, Hawaiian and a number of other Polynesian languages do make such a distinction; cf. Hawaiian /ahi/ "fire", /ʔahi/ "tuna".)
This means that the difference between a syllable with a null onset and one beginning with a glottal stop is often purely a difference of phonological analysis, rather than the actual pronunciation of the syllable. In some cases, the pronunciation of a (putatively) vowel-initial word when following another word – particularly, whether or not a glottal stop is inserted – indicates whether the word should be considered to have a null onset. For example, many Romance languages such as Spanish never insert such a glottal stop, while English does so only some of the time, depending on factors such as conversation speed; in both cases, this suggests that the words in question are truly vowel-initial. But there are exceptions here, too. For example, German and Arabic both require that a glottal stop be inserted between a word and a following, putatively vowel-initial word. Yet such words are said to begin with a vowel in German but a glottal stop in Arabic. The reason for this has to do with other properties of the two languages. For example, a glottal stop does not occur in other situations in German, e.g. before a consonant or at the end of word. On the other hand, in Arabic, not only does a glottal stop occur in such situations (e.g. Classical /saʔala/ "he asked", /raʔj/ "opinion", /dˤawʔ/ "light"), but it occurs in alternations that are clearly indicative of its phonemic status (cf. Classical /kaːtib/ "writer" vs. /maktuːb/ "written", /ʔaːkil/ "eater" vs. /maʔkuːl/ "eaten").
The writing system of a language may not correspond with the phonological analysis of the language in terms of its handling of (potentially) null onsets. For example, in some languages written in the Latin alphabet, an initial glottal stop is left unwritten; on the other hand, some languages written using non-Latin alphabets such as abjads and abugidas have a special zero consonant to represent a null onset. As an example, in Hangul, the alphabet of the Korean language, a null onset is represented with ㅇ at the left or top section of a grapheme, as in 역 "station", pronounced yeok, where the diphthong yeo is the nucleus and k is the coda.
Famous quotes containing the word onset:
“While the onset of puberty can vary by as much as six years, every adolescent wants to be right on the 50-yard line, right in the middle of the field. One is always too tall, too short, too thin, too fat, too hairy, too clear-skinned, too early, too late. Understandably, problems of self-image are rampant.”
—Joan Lipsitz (20th century)