本文以「優選理論」觀點討論臺灣閩南語的運讀變調。在聲調制約方面，Ident-T-R與*T2/D並列為最高層級制約，確保最右端之聲調有相同的表層對應，並避免在局部範疇中出現兩個或兩個以上之有標成分。在韻律制約方面，取決於AlignP-R，將音韻詞組右端與XP右竟對齊，句法與音韻之介面則可進一步藉由「對應理論」來詮釋。

　　　　　This paper discusses tone sandhi in Taiwanese from the perspective of the Optimality Theory. Ident-T-R and *T2/D are ranked the highest among the tonal constraints, ensuring that the rightmost tone has an output correspondence and that no more than one marked element occurs in a local domain. AlignP-R is a central prosodic constraint, which aligns the right edge of a phonological phrase with the right edge of a XP, while the syntax-phonology interface can be further accounted for by the Correspondence Theory.