Vowel

元音

One of the two general categories used for the classification of speech sounds, the other being consonant. Phonetically, they are sounds articulated without a complete closure in the mouth or a degree of narrowing which would produce audible friction; the air escapes evenly over the centre of the tongue. If air escapes solely through the mouth, the vowels are said to be oral; if some air is simultaneously released through the nose, the vowels are nasal. In addition to this, in a phonetic classification of vowels, reference would generally be made to two variables, the first of which is easily describable, the second much less so: (a) the position of the lips - whether rounded, spread, or neutral; (b) the part of the tongue raised, and the height to which it moves.

Relatively slight movements of the tongue produce quite distinct auditory differences in vowel (or vocalic) quality. Because it is very difficult to see or feel these movements, classification of vowels is usually carried out using acoustic or auditory criteria, supplemented by details of lip position. There are several systems for representing vowel position visually, e.g. in terms of a vowel triangle or a vowel quadrilateral such as the cardinal vowel system.

In establishing the vowel system of a language, several further dimensions of classification may be used. One criterion is in terms of the duration of the vowel (whether relatively ‘long’ or ‘short’ vowels are used). Another is whether, during an articulation, there is any detectable change in quality. If the quality of a vowel stays unchanged, the term pure vowel, or monophthong, is used. If there is an evident change in quality, one talks instead of a gliding vowel. If two auditory elements are involved, the vowel glide is referred to as a diphthong; if three elements, as a triphthong. In the distinctive feature theory of phonology, the term vocalic is used as the main feature in the analysis of vowel sounds.

Yet another way of classifying vowels is in terms of the amount of muscular tension required to produce them: vowels articulated in extreme positions are more ‘tense’ than those articulated nearer the centre of the mouth, which are ‘lax’.

给语音分类的两大范畴之一，另一个范畴是辅音。元音可从语音学和音系学两方面定义。语音学上，元音是口腔内没有完全闭塞或收窄程度不足以产生可闻摩擦时发出的音；气流均匀地从舌中央上方逸出。如果空气只从口腔逸出，这样的元音是口元音；如果一部分空气同时从鼻腔逸出，这样的元音是鼻元音。此外，语音学给元音分类一般参考两个变项，第一个容易描写，第二个描写较困难：（a）双唇的位置—是圆唇、展唇还是中性；（b）舌上抬的部分和上抬的高度。

舌的较小动作就会在元音音质上产生明显的听觉差异。由于观察或感觉这些动作十分困难，元音的分类通常采用声学或听觉标准，辅之以详细的唇位。从视觉上表示元音位置的方式有好几种系统，例如用“元音三角形”或“元音四边形”表示的基本元音系统。

在建立一种语言的元音系统时还可从其他几个方面给元音分类。一个标准是元音的时长（相对而言是“长”元音还是“短”元音）。另一个标准是发音过程中音质有无可觉察的变化。如果一个元音的音质保持不变，就称作纯元音或单元音。如果音质有明显变化，就称作滑元音。如果包含两个听觉成分，这样的元音滑音称作二合元音；如果包含三个成分，称作三合元音。在音系学的区别特征理论中，元音性用作元音分析的主要特征。

然而还有一种元音的分类是按照发音时所需的肌肉紧度：在极端位置发出的元音比较“紧”，在接近口腔中央位置发出的元音比较“松”。