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.[1] Examples of semivowels in English are the consonants y and w in yes and west, respectively. Written /j w/ in IPA, y and w are near to the vowels ee and oo in seen and moon, written /iː uː/ in IPA. The term glide may alternatively refer to any type of transitional sound, not necessarily a semivowel.[2]
Semivowels form a subclass of approximants.[3][4] Although "semivowel" and "approximant" are sometimes treated as synonymous,[5] 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, Ladefoged & Maddieson (1996) do not consider the labiodental approximant [ʋ] to be a semivowel.[6]
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]
In addition, some authors[6][7] consider the rhotic approximants [ɹ], [ɻ] to be semivowels corresponding to R-colored vowels such as [ɚ]. An unrounded central semivowel, [j̈] (or [j˗]), equivalent to [ɨ], is uncommon, though rounded [ẅ] (or [w̟]), equivalent to [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.[3] In languages such as Amharic, Yoruba, and Zuni, semivowels are produced with a narrower constriction in the vocal tract than their corresponding vowels.[6] 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].[8]
It is unusual for a language to contrast a semivowel and a diphthong containing an equivalent vowel,[citation needed] but Romanian contrasts the diphthong /e̯a/ with /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 /e/ in singular-plural pairs), there are phonetic differences between the pair:[9]
Although a phonological parallel exists between /o̯a/ and /wa/, the production and perception of phonetic contrasts between the two is much weaker, likely because of lower lexical load for /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.[10]
According to the standard definitions, semivowels (such as [j]) contrast with fricatives (such 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.[11] Though the spirant approximant is more constricted (having a lower F2 amplitude), longer, and unspecified for rounding (viuda [ˈbjuða] 'widow' vs. ayuda [aˈʝʷuða] 'help'),[12] 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 [ãˈnjeɣo] ('flood')[13] and although there is dialectal and idiolectal variation, speakers may also exhibit other near-minimal pairs like abyecto ('abject') vs. abierto ('opened').[14] One potential minimal pair (depending on dialect) is ya visto [(ɟ)ʝaˈβisto] ('already seen') vs. y ha visto [jaˈβisto] ('and he has seen').[15]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 ([ʒ]), like in Rioplatense Spanish.
