口語中的常用詞往往說得極弱或粗率，容易使其語音形式發生音變規律之外的特殊變化。本文將這一現象稱做 “輕讀音變”。“輕讀音變” 中一個重要類型是介音的脫落，它又可分為介音 i 的脫落和介音 u 脫落。介音的脫落，特別是介音 i 的脫落，也會引起聲母、韻母的例外演變。本文對這些 “輕讀” 使介音脫落的例子加以具體的分析，附帶也討論 “輕讀音變” 的一些一般性問題。

　　In Chinese, the dropping of the medial vowels i and u is one of the main types of irregular sound changes caused by weak or slurred pronunciation, which are often found in the history of grammatical words. The dropping of the medial vowels itself might be the cause of some irregular changes of the initial consonants or final vowels. The author cites some instances of the type, and explains how the phonetic shapes of the Chinese grammatical words underwent the influence of the dropping of medial vowels.

介音; 常用詞; 輕讀; 例外音變

medial vowels; grammatical words; weak pronunciation; irregular sound change