Semivowel

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In phonetics and phonology, a semivowel or glide 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.[1] Examples of semivowels in English are the consonants y and w, in yes and west, respectively. Written w/ 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.[2]

Classification

Semivowels form a subclass of approximants.[3][4] Although "semivowel" and "approximant" are sometimes treated as synonymous,[5] most authors use the term "approximant" for a more restricted set; there is no universally agreed upon definition, and the exact details may vary from author to author. For example, Ladefoged & Maddieson (1996) do not consider the labiodental approximant [ʋ] to be a semivowel[6] while Martínez Celdrán (2004) proposes that it should be considered one.[7]

In the International Phonetic Alphabet, the diacritic attached to non-syllabic vowel letters is an inverted breve placed below the symbol representing the vowel: U+032F  ̯  COMBINING INVERTED BREVE BELOW. When there is no room for the tack under a symbol, it may be written above, using U+0311  ̑  COMBINING INVERTED BREVE. Before 1989, non-syllabicity was represented by U+0306  ̆  COMBINING BREVE, which now stands for extra-shortness.

Additionally, there are dedicated symbols for four semivowels that correspond to the four close cardinal vowel sounds:[4]

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)

The pharyngeal approximant [ʕ̞] is also equivalent to the semivowel articulation of the open back unrounded vowel [ɑ].[6]

In addition, some authors[6][7] 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. An unrounded central semivowel, [ ȷ̈ ], equivalent to [ɨ], is uncommon, though rounded [ẅ] (or [w̟]), equivalent to [ʉ], is found in Swedish and Norwegian.