閩南語讀書音陽聲韻尾 -iong 與白話音的對應是鼻化韻尾 -iõ（漳州腔）、-iũ（泉州腔），但在其演變過程中，有些字並不如此。本文以「相」（siong）字爲例說明之，其白話音應是 siõ、siũ，卻有 sio（漳腔）、siu、sa（泉腔）等不含鼻化韻的音，尤其在泉州梨園戲及南管唱詞中更爲明顯。本文分五部分：
　　一、說明陽聲韻與鼻化韻的演變規律。
　　二、以 1566 年出版的閩南白話南戲劇本《荔鏡記》的韻腳字作爲 -iõ→-iũ 的例證。
　　三、舉出「相」字失去鼻化韻的例子，主要以南管曲詞爲例，舉出其唱音有 siu、sa 二音，此屬泉州音；而漳州音 sio 亦失去鼻化韻，今日仍如此說。爲何如此？在「相逢」、「相戲」、「相交」、「相隨」、「相共」等詞中，「相」字是虛詞，口語連讀時，虛詞易趨向於簡化，遂使本有的鼻化韻消失，即 sã pang5（相逢）→sa pang5。
　　四、以「相共」（sio/sã kang7）一詞爲例，說明此詞在民問使用的普遍情形。
　　五、以今日台語文作家之用字，說明「相V（動詞）」的詞組，易「相」爲「肖」之不妥作結。

　　The rising coda -iong is a reading phone in Taiwanese. Its allophone of vernacular phone is the nasalized -iõ (Zhang-Zhou accent) and -iũ (Quan-Zhou accent). This study gives siong 相 as an example to demonstrate that some sounds do not follow this rule and they underwent other sound change. Though the vernacular phone of siong is sio, siu, there are unnasalized siõ (Zhang-Zhou accent), siũ and sa (Quan-Zhou accent). It is particularly common in the lyrics of Quan-Zhou operatic circle and nan kuan.
　　This paper is structured as follows: (1) The rule of the sound change: rising coda→nasalization. (2) The -iõ→-iũ change will be illustrated with rhyming words appeared in Lijingji (A script written in Taiwanese vernacular phones published in l566). (3) 相 without nasalization: Examples in this section are for the most part taken from Nan kuan lyrics where siu and sa (Quan-Zhou accent) as well as sio (Zhang-Zhou accent) lost their nasal codas. What is the reason that we still utter these phones? The 相 is a function word, as in siõ/sã pang (to meet). siõ/sã hi (to play together), siõ/sã kau (to make acquaintance), siõ/sã sui (to follow) and siõ/sã kang (to resemble). Function words tend to be simplified when being articulated. The nasalization thus disappears, i.e. sã pang5→sa pang5 (to meet). (4) This section recounts siõ/sã kong7 (to resemble) and its common usages by speakers. (5) At last, we state the 相-VP used by Taiwanese writers and the inaccuracy to replace 相 with 肖.

鼻音韻尾; 鼻化韻; 弱化; 讀書音; 白話音; 相共

nasalized coda; nasalization; reduction; reading phone; vernacular phone; siõ/sã kong7