|Manners of articulation|
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In phonetics and phonology, a semivowel (or glide) is a sound, such as English // or //, that is phonetically similar to a vowel sound but functions as the syllable boundary rather than as the nucleus of a syllable.
Semivowels form a subclass of approximants. Although "semivowel" and "approximant" are sometimes treated as synonymous, most authors agree that not all approximants are semivowels, although the exact details may vary from author to author. For example, Ladefoged & Maddieson (1996) don't consider the labiodental approximant [ʋ] to be a semivowel, while Martínez-Celdrán (:2004) proposes that it should be considered one.
In the International Phonetic Alphabet, the diacritic attached to non-syllabic vowel letters is ⟨ ̯ ⟩ (U+032F ̯ combining inverted breve below). Additionally, there are dedicated letters for four semivowels that correspond to the four close cardinal vowel sounds:
|Semivowel (non-syllabic)||Vowel (syllabic)|
|[j] (palatal approximant)||[i] (close front unrounded vowel)|
|[ɥ] (labio-palatal approximant)||[y] (close front rounded vowel)|
|[ɰ] (velar approximant)||[ɯ] (close back unrounded vowel)|
|[w] (labiovelar approximant)||[u] (close back rounded vowel)|
In addition, some authors consider the rhotic approximants [ɹ], [ɻ ] to be semivowels corresponding to R-colored vowels such as [ɚ]. As mentioned above, the labiodental approximant [ʋ] is considered a semivowel in some treatments. A central semivowel, [ ȷ̈ ] (also written [ ɉ ]), is uncommon. The semivowel corresponding to the close mid front unrounded vowel,[clarification needed] here provisionally defined as "semipalatal semilateral" approximant, is currently attested only[dubious ] in some varieties of Venetian as an allophone of the lateral consonant /l/ and can also be reduced to zero.
Contrast with vowels 
Semivowels, by definition, contrast with vowels by being non-syllabic. In addition, they are usually shorter than vowels. In languages as diverse 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 [flaɪ̯], or as a closed syllable ending in a consonant [flaj].
It is unusual for a language to contrast a semivowel and a diphthong containing an equivalent vowel, however, Romanian contrasts the diphthong /e̯a/ with /ja/, a perceptually similar approximant–vowel sequence. The diphthong is analyzed as a single segment while the approximant–vowel sequence is analysed as two separate segments. In addition to phonological justifications for the distinction (such as the diphthong alternating with /e/ in singular–plural pairs), there are phonetic differences between the pair:
- /ja/ has a greater duration than /e̯a/
- The transition between the two elements is longer and faster for /ja/ than /e̯a/ with the former having a higher F2 onset (i.e. greater constriction of the articulators).
Although a phonological parallel exists between /o̯a/ and /wa/, the production and perception of phonetic contrasts between the two is much weaker, likely due to a lower lexical load for /wa/ (which is limited largely to loanwords from French) and a difficulty in maintaining contrasts between two back rounded glides in comparison to front ones.
Contrast with fricatives/spirant approximants 
According to the standard definitions, semivowels (such as [j]) contrast with fricatives (such as [ʝ]) in that fricatives produce turbulence, while 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 (e.g. viuda [ˈbjuða] 'widow' vs ayuda [aˈʝʷuða] '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 /l/ and /n/: enyesar [ẽɲɟʝeˈsaɾ] ('to plaster') aniego [ãnjeɣo] ('flood') and, although there is dialectal and ideolectal 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 [(ɟ)ʝaˈβisto] ('I have already seen') vs y ha visto [jaˈβisto] ('and he has seen'). Again, this is not present in all dialects. Other dialects differ in either merging the two or in enhancing the contrast by moving the former to another place of articulation (e.g. [ʒ]).
See also 
- List of phonetics topics
- Syllabic consonant
- Vowel cluster
- Hiatus (linguistics)
- Voiced labio-velar approximant
- Ladefoged & Maddieson (1996:322)
- Crystal (2003:413)
- Martínez-Celdrán (2004:9)
- Meyer (2005:101)
- Ladefoged & Maddieson (1996:323)
- Martínez-Celdrán (2004:8)
- The International Phonetic Alphabet in Unicode, UCL Division of Psychology & Language Sciences
- Cohen (1971:51)
- Chitoran (2002:212–214)
- Chitoran (2002:221)
- Martínez-Celdrán (2004:6)
- Martínez-Celdrán (2004:208)
- Trager (1942:222)
- Saporta (1956:288)
- Bowen & Stockwell (1955:236)
- Bowen, J. Donald; Stockwell, Robert P. (1955), "The Phonemic Interpretation of Semivowels in Spanish", Language (Linguistic Society of America) 31 (2): 236–240, doi:10.2307/411039, JSTOR 411039
- Chitoran, Ioana (2002), "A perception-production study of Romanian diphthongs and glide-vowel sequences", Journal of the International Phonetic Association 32 (2): 203–222, doi:10.1017/S0025100302001044
- Crystal, David (2003), A dictionary of linguistics & phonetics (fifth ed.), Wiley-Blackwell, ISBN 0-631-22664-8
- Cohen, Antonie (1971), The phonemes of English: a phonemic study of the vowels and consonants of standard English (third ed.), Springer, ISBN 90-247-0639-4
- Ladefoged, Peter; Maddieson, Ian (1996). The Sounds of the World's Languages. Oxford: Blackwell. ISBN 0-631-19814-8.
- Martínez-Celdrán, Eugenio (2004), "Problems in the Classification of Approximants", Journal of the International Phonetic Association 34 (2): 201–210, doi:10.1017/S0025100304001732
- Meyer, Paul Georg (2005), Synchronic English Linguistics: An Introduction (third ed.), Tübingen: Gunter Narr Verlag, ISBN 3-8233-6191-0
- Saporta, Sol (1956), "A Note on Spanish Semivowels", Language (Linguistic Society of America) 32 (2): 287–290, doi:10.2307/411006, JSTOR 411006
- Trager, George (1942), "The Phonemic Treatment of Semivowels", Language (Linguistic Society of America) 18 (3): 220–223, doi:10.2307/409556, JSTOR 409556
Further reading 
- Ohala, John; Lorentz, James, "The story of [w]: An exercise in the phonetic explanation for sound patterns", in Whistler, Kenneth; Chiarelloet, Chris; van Vahn, Robert Jr., Proceedings of the 3rd Annual Meeting of the Berkeley Linguistics Society, Berkeley: Berkeley Linguistic Society, pp. 577–599