Semivowel

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 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]

Classification

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 inverted breve 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)

Some authors argue for the recognition of additional semivowels:

• The rhotic approximants ⟨ɹ⟩ and ⟨ɻ⟩, considered to be semivowels corresponding to r-colored vowels such as ⟨ɚ⟩ or ⟨ɝ⟩.^[6][7]
• The pharyngeal approximant ⟨ʕ̞⟩, considered to be the semivowel corresponding to the open back vowel ⟨ɑ⟩,^[8] which is noted to have distinct pharyngeal features in its articulation.^[9]
• The post-palatal approximants,^[10] or central semivowels, which may be written as ⟨j˗ ɥ˗ w̟⟩ (diacritics for advancing and retracting), ⟨ȷ̈ ɥ̈ ẅ⟩ (diacritics for centralization), or the para-IPA symbols ⟨ɉ ɥ w⟩,^[11] considered to be corresponding to the unrounded ⟨ɨ⟩, compressed ⟨ÿ⟩, and protruded ⟨ʉ⟩ close central vowels, respectively.

Contrast with vowels

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 [flai̯] or as a closed syllable ending in a consonant [flaj].^[12]

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:^[13]

• /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 (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 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.^[14]

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, 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.^[15] Though the spirant approximant is more constricted (having a lower F2 amplitude), longer, and unspecified for rounding (viuda [ˈbjuða] 'widow' vs. ayuda [aˈʝʷuða] 'help'),^[16] 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') vs. aniego [ãˈnjeɣo] 'flood',^[17] and although there is dialectal and idiolectal variation, speakers may also exhibit other near-minimal pairs like abyecto [aβ̞ˈʝe̞tːo̞] 'abject' vs. abierto [aβ̞ˈje̞tːo̞] 'opened'.^[18] One potential minimal pair (depending on dialect) is ya visto [(ɟ)ʝaˈβisto] 'already seen' vs. y ha visto [jaˈβisto] 'and he has seen'.^[19]

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.

See also

• Diphthong
• Hiatus (linguistics)
• List of phonetics topics
• Mater lectionis
• Syllabic consonant
• Voiced labio-velar approximant