双元音

双元音（diphthong）是一种复元音（compound vowel），又称双元音或二合复元音，在语音学中，指联合的两个元音，它们作为一个整体出现。之间有平滑的过渡，也就是说，双元音中的发音牵涉到两种不同的舌位，并且从其中一种舌位滑动到另一舌位。在国际音标 (IPA) 中，单元音用一个字母表示，如[ʌ]。双元音用两个字母表示，如[aɪ]，响度较低的字母可以加上  ̯ 符号以表示它是双元音的一部分，例如 [aɪ̯]。

关于拼字时两个一组的元音字母，且通常不分别发成两个元音的情况，请见“二合字母”。

American English pronunciation of no highway cowboys, showing five diphthongs: /oʊ aɪ eɪ aʊ ɔɪ/

双元音的类型

双元音依响度的变化可分为上升双元音与下降双元音（或称上升复元音与下降复元音）。上升复元音以响度较低的元音开始，以响度较高的元音结束，例如 [ɪ̯a]。下降复元音以响度较高的元音开始，以响度较低的元音结束，例如 [aɪ̯]。在某些语言或研究中，会将下降复元音视为真正的双元音，至于上升复元音则倾向于被当作相邻出现的两个元音。例如在汉语中，上升复元音常被当作介音与主要元音的结合，而下降复元音则被当作一个整体的押韵单位。

参见

• 音位变异（英语：Phonemic differentiation）
• 三元音

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