本文討論天津話多字組連讀變調現象中，構詞句法結構伴隨字組增長而影響增加的現象，並提出優選理論（Optimality Theory；Prince &Smolensky 1993/2004，McCarthy & Prince 1993）的分析。天津話連讀變調的特殊之處在於其三字組變調雖不受構詞句法結構規範，但從四字組開始，構詞句法結構又逐漸影響變調。文獻上對於天津話連讀變調是否受構詞句法結構影響的看法不一。本文認為天津話連讀變調基本上不受構詞句法結構影響。大於三音節的聲調組合之所以開始受構詞句法結構影響，乃因天津話限定其聲調範疇不得大於三音節。因此，當聲調組合大於三音節時，就會被拆成較小的範疇；在將聲調組合拆成較小範疇時並非任意武斷的，而是受到構詞句法結構影響。三字組變調範疇不受構詞句法結構規範，多字組變調範疇反受其影響；兩種變調範疇看似十分不同，卻可由同一組制約位階得到預測。

This paper examines the morphosyntactic sensitivity of Tianjin 天津 tonesandhi and proposes an analysis based on Optimality Theory. Tianjin tonesandhi is unique in that while tone sandhi in tri-tonal strings is insensitive tomorphosyntactic structures, morphosyntactic structures start to influence tonesandhi in longer strings. Scholars disagree with respect to whether Tianjin tonesandhi is sensitive to morphosyntactic structures. The present paper holds theposition that Tianjin tone sandhi is basically insensitive to morphosyntacticstructures and argues that the reason tone sandhi starts to be influenced bymorphosyntactic structures is due to the fact that Tianjin has an upper limittowards the domain (foot) size. Thus, when the tonal strings exceed 3 syllables,the strings are divided into independent feet. The separation of the tonal stringsinto different feet is not ad-hoc, but is sensitive to morphosyntactic structures.