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Approximants are speech sounds that involve the articulators approaching each other but not narrowly enough nor with enough articulatory precision〔, citing 〕 to create turbulent airflow. Therefore, approximants fall between fricatives, which do produce a turbulent airstream, and vowels, which produce no turbulence. This class of sounds includes lateral approximants like (as in ''less''), non-lateral approximants like (as in ''rest''), and semivowels like and (as in ''yes'' and ''west'', respectively).〔 Before Peter Ladefoged coined the term "approximant" in the 1960s,〔, pointing to 〕 the term "frictionless continuant" referred to non-lateral approximants. ==Semivowels== (詳細はsemivowel'' and ''glide'' are often used for these non-syllabic vowel-like segments. The correlation between semivowels and vowels is strong enough that cross-language differences between semivowels correspond with the differences between their related vowels.〔, citing 〕 Vowels and their corresponding semivowels alternate in many languages depending on the phonological environment, or for grammatical reasons, as is the case with Indo-European ablaut. Similarly, languages often avoid configurations where a semivowel precedes its corresponding vowel.〔, citing 〕 A number of phoneticians distinguish between semivowels and approximants by their location in a syllable. Although he uses the terms interchangeably, remarks that, for example, the final glides of English ''par'' and ''buy'' differ from French ''par'' ('through') and ''baille'' ('tub') in that, in the latter pair, the approximants appear in the syllable coda, whereas, in the former, they appear in the syllable nucleus. This means that opaque (if not minimal) contrasts can occur in languages like Italian (with the i-like sound of ''piede'' 'foot', appearing in the nucleus: , and that of ''piano'' 'slow', appearing in the syllable onset: ) and Spanish (with a near minimal pair being ''abyecto'' 'abject' and ''abierto'' 'opened'). : : Because of the articulatory complexities of the American English rhotic, there is some variation in its phonetic description. A transcription with the IPA character for an alveolar approximant () is common, though the sound is more postalveolar. Actual retroflexion may occur as well and both occur as variations of the same sound.〔 citing , , and 〕 However, makes a distinction between the vowels of American English (which he calls "rhotacized") and vowels with "retroflexion" such as those that appear in Badaga; , on the other hand, labels both as r-colored and notes that both have a lowered third formant.〔Both cited in 〕 : Because the vowels are articulated with spread lips, spreading is implied for their approximant analogues, . However, these sounds generally have little or no lip-spreading. The fricative letters with a lowering diacritic, , may therefore be justified for a neutral articulation between spread and rounded .〔 John Esling (2010) "Phonetic Notation", in Hardcastle, Laver & Gibbon (eds) ''The Handbook of Phonetic Sciences'', 2nd ed., p 699.〕 In articulation and often diachronically, palatal approximants correspond to front vowels, velar approximants to back vowels, and labialized approximants to rounded vowels. In American English, the rhotic approximant corresponds to the rhotic vowel. This can create alternations (as shown in the above table). In addition to alternations, glides can be inserted to the left or the right of their corresponding vowels when occurring next to a hiatus. For example, in Ukrainian, medial triggers the formation of an inserted that acts as a syllable onset so that when the affix is added to футбол ('football') to make футболіст 'football player', it's pronounced but маоїст ('Maoist'), with the same affix, is pronounced with a glide. Dutch has a similar process that extends to mid vowels: * ''bioscoop'' → ('cinema') * ''zee'' + ''en'' → ('seas') * ''fluor'' → ('fluor') * ''reu'' + ''en'' → ('male dogs') * ''Rwanda'' → ('Rwanda')〔There is dialectal and allophonic variation in the realization of . For speakers who realize it as , postulates an additional rule that changes any occurrence of from glide insertion into .〕 * ''Boaz'' → ('Boaz')〔 Similarly, vowels can be inserted next to their corresponding glide in certain phonetic environments. Sievers' law describes this behaviour for Germanic. Non-high semivowels also occur. In colloquial Nepali speech, a process of glide-formation occurs, wherein one of two adjacent vowels becomes non-syllabic; this process includes mid vowels so that ('cause to wish') features a non-syllabic mid vowel. Spanish features a similar process and even nonsyllabic can occur so that ''ahorita'' ('right away') is pronounced . It is not often clear, however, whether such sequences involve a semivowel (a consonant) or a diphthong (a vowel), and in many cases that may not be a meaningful distinction. Although many languages have central vowels , which lie between back/velar and front/palatal , there are few cases of a corresponding approximant . One is in the Korean diphthong or ,〔(Ahn & Iverson (2006) )〕 though this is more frequently analyzed as velar (as in the table above), and Mapudungun may be another: It has three high vowel sounds, , , and three corresponding consonants, , and , and a third one is often described as a voiced unrounded velar fricative; some texts note a correspondence between this approximant and that is parallel to – and –. An example is ''liq'' (?) ('white').〔Listen to a (recording )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「approximant consonant」の詳細全文を読む スポンサード リンク
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