pronounced as /notice/
In phonetics and phonology, a semivowel, glide or semiconsonant is a sound that is phonetically similar to a vowel sound but functions as the syllable boundary, rather than as the nucleus of a syllable. Examples of semivowels in English are the consonants y and w in yes and west, respectively. Written in IPA, y and w are near to the vowels ee and oo in seen and moon, written in IPA. The term glide may alternatively refer to any type of transitional sound, not necessarily a semivowel.
Semivowels form a subclass of approximants. Although "semivowel" and "approximant" are sometimes treated as synonymous, most authors use the term "semivowel" for a more restricted set; there is no universally agreed-upon definition, and the exact details may vary from author to author. For example, do not consider the labiodental approximant pronounced as /[ʋ]/ to be a semivowel.
In the International Phonetic Alphabet, the diacritic attached to non-syllabic vowel letters is an inverted breve placed below the symbol representing the vowel: . When there is no room for the tack under a symbol, it may be written above, using . Before 1989, non-syllabicity was represented by, which now stands for extra-shortness.
Additionally, there are dedicated symbols for four semivowels that correspond to the four close cardinal vowel sounds:
| Semivowel (non-syllabic) | Vowel (syllabic) | |
|---|---|---|
| pronounced as /link/ (palatal approximant) | pronounced as /link/ (close front unrounded vowel) | |
| pronounced as /link/ (labio-palatal approximant) | pronounced as /link/ (close front rounded vowel) | |
| pronounced as /link/ (velar approximant) | pronounced as /link/ (close back unrounded vowel) | |
| pronounced as /link/ (labiovelar approximant) | pronounced as /link/ (close back rounded vowel) |
In addition, some authors consider the rhotic approximants pronounced as /link/, pronounced as /link/ to be semivowels corresponding to R-colored vowels such as pronounced as /link/. An unrounded central semivowel, pronounced as /[j̈]/ (or pronounced as /[j˗]/), equivalent to pronounced as /[ɨ]/, is uncommon, though rounded pronounced as /[ẅ]/ (or pronounced as /[w̟]/), equivalent to pronounced as /[ʉ]/, is found in Swedish and Norwegian.
Semivowels, by definition, contrast with vowels by being non-syllabic. In addition, they are usually shorter than vowels. In languages such as Amharic, Yoruba, and Zuni, semivowels are produced with a narrower constriction in the vocal tract than their corresponding vowels. Nevertheless, semivowels may be phonemically equivalent with vowels. For example, the English word fly can be considered either as an open syllable ending in a diphthong pronounced as /[flaɪ̯]/ or as a closed syllable ending in a consonant pronounced as /[flaj]/.
It is unusual for a language to contrast a semivowel and a diphthong containing an equivalent vowel, but Romanian contrasts the diphthong pronounced as //e̯a// with pronounced as //ja//, a perceptually similar approximant-vowel sequence. The diphthong is analyzed as a single segment, and the approximant-vowel sequence is analyzed as two separate segments.
In addition to phonological justifications for the distinction (such as the diphthong alternating with pronounced as //e// in singular-plural pairs), there are phonetic differences between the pair:
Although a phonological parallel exists between pronounced as //o̯a// and pronounced as //wa//, the production and perception of phonetic contrasts between the two is much weaker, likely because of lower lexical load for pronounced as //wa//, which is limited largely to loanwords from French, and speakers' difficulty in maintaining contrasts between two back rounded semivowels in comparison to front ones.
According to the standard definitions, semivowels (such as pronounced as /[j]/) contrast with fricatives (such as pronounced as /[ʝ]/) in that fricatives produce turbulence, but semivowels do not. In discussing Spanish, Martínez Celdrán suggests setting up a third category of "spirant approximant", contrasting both with semivowel approximants and with fricatives. Though the spirant approximant is more constricted (having a lower F2 amplitude), longer, and unspecified for rounding (viuda pronounced as /[ˈb'''ju'''ða]/ 'widow' vs. ayuda pronounced as /[aˈ'''ʝʷu'''ða]/ 'help'), the distributional overlap is limited. The spirant approximant can only appear in the syllable onset (including word-initially, where the semivowel never appears). The two overlap in distribution after pronounced as //l// and pronounced as //n//: enyesar pronounced as /[ẽɲ'''ɟʝ'''eˈsaɾ]/ ('to plaster') aniego pronounced as /[ãˈn'''j'''eɣo]/ ('flood') and although there is dialectal and idiolectal variation, speakers may also exhibit other near-minimal pairs like abyecto ('abject') vs. abierto ('opened'). One potential minimal pair (depending on dialect) is ya visto pronounced as /['''(ɟ)ʝa'''ˈβisto]/ ('already seen') vs. y ha visto pronounced as /['''ja'''ˈβisto]/ ('and he has seen').Again, it is not present in all dialects. Other dialects differ in either merging the two or enhancing the contrast by moving the former to another place of articulation (pronounced as /[ʒ]/), like in Rioplatense Spanish.