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. 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 i:_u: 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 [ʋ] to be a semivowel, while proposes that it should be considered one. 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: The pharyngeal approximant [ʕ̞] is also equivalent to the semivowel articulation of the open back unrounded vowel [ɑ]. 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. 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.