本論文以優選理論探討上海話之入聲變調，試圖將文獻中所認為表現不規律之入聲變調納入與舒聲變調相容之分析中。本研究認為入聲變調與舒聲變調皆受制於ANCHOR-L(tσ1, Hd)，因此其首音節之基底聲調在輸出值中皆出現於重讀音節。以此觀之，則入聲變調與舒聲變調的差異主要在於節律重音的位置：在舒聲變調中首音節重讀；在入聲變調中重音則後移──在陰入變調中係移至第二音節，在陽入變調中則移至末音節。 本論文提出兩點假設：上海話中舒聲音節為重量音節，入聲音節為輕量音節；節律結構基本上為一位於左端之雙音節音步。據此，本研究提出COINCIDE (LightHd, FT-final)，認為陰入變調中重音所以後移至第二音節是因為重讀之輕量音節傾向於由音步末音節核可(licensing)。另一方面，由於陽入的單字調為曲拱調，與陰入的水平調有別，是以本研究另外提出COINCIDE(Contour, PrWd-final)，此制約顯示陽入變調中重音的遠距移位是為了遵行「曲拱調須由末音節核可」之普遍現象。 綜述之，本論文提供了一個重量音節、節律重音、曲拱調以及邊際位置等韻律顯著位置間彼此對映的實例。此外，本研究亦顯示上海話的連讀變調涉及聲調與重音的互動，是以所提出之分析或許對相關類型之研究亦有所貢獻。 / This thesis offers an Optimality-theory approach to the tone sandhi of checked tones (TSC) in Shanghai, in an attempt to regulate its surface patterns which have long been considered anomaly as opposed to the tone sandhi of smooth tones (TSS). With a reanalysis in the present study, TSC and TSS arguably have in common that their process of tone mapping is both subject to ANCHOR-L(tσ1, Hd), by which the un- derlying tone of the initial syllable ends up at the stressed syllable in the output. It follows that TSC is different from TSS in the way that metrical head is assigned: all domains undergoing TSS are stressed on their initial syllable; only in domains of TSC does the stress move rightwards, either to the second place in the tone sandhi of Yinru (TSYI), or to the final syllable in the tone sandhi of Yangru (TSYA). Given the assumption that checked syllables and smooth syllables in Shanghai are light and heavy, respectively, in terms of moraicity, and that foot-parsing is binary and left-aligned in general, the one-syllable shift of stress in TSYI can be accounted for by positing COINCIDE(LightHd, FT-final), which sets up the preference for light stress- bearing syllables to be licensed foot-finally. On the other hand, given that Yangru in the citation forms represents a rising contour, different from the level tone of Yinru, a licensing constraint, namely COINCIDE(Contour, PrWd-final), is further posited so that the long-distance movement of metrical head observed in TSYA emerges to satisfy the requirement for the retained rising contour to be licensed word-finally. Taken together, this thesis instantiates a remarkable case of the mapping among multiple prominent positions, including heavy syllables, metrical head, contour tones, and edge positions. Also, the present analysis demonstrates that Shanghai tone sandhi involves an interaction between tone and stress, thus a contribution to the general OT tone-prominence typology literature (cf. Zhang 2001, Barnes 2002, De Lacy 2002).