本研究以日文「そうだ」為對象，著眼於其「樣態」用法衍生為「非斷定表現」的演變過程，以語用論的觀點，考察非斷定表現「そうだ」實際出現於談話及文章中的使用狀況。本論文中，筆者透過語料庫等電子資源檢索相關例句，並設定（1）命題的屬性及話者的發言權、（2）表現意圖及發話機能、（3）構文（句子結構）此三大基準，針對「そうだ」在文章及談話中的使用語境及語用論要素等進行考察，同時歸納整理出常與非斷定表現「そうだ」共同使用的語彙及句型等。分析結果顯示，非斷定表現「そうだ」大多使用於「理解要請－說明‧意見」、「自己表明－評價」、「働きかけ－助言・忠告」以及「表明回避」此類談話機能及語境，此考察結果除了建構非斷定表現「そうだ」的語用機能架構，亦可運用於日語教育的教學指導上。

This research focuses on the changing process of non-assertive expression, ”souda,” derived from its similarity usage, and examines the context functions from the perspective of Pragmatics. Throughout corpus data-collection, I analyzed the discourse situation and speaker's utterance intention of ”souda” on the basis of (1) proposition property and speaker's voice, (2) intention and function, (3) sentence structure. The analysis result shows that the non-assertive expression, ”souda,” is often used in the discourse situations, such as ”comprehension request: explanation, opinion,” ”self expression: valuation,” ”promotion: suggestion,” and ”expression evasion.” The research result provides a useful framework for the Pragmatic function of non-assertive expression, ”souda,” and proposes a better pedagogy which can be applied to the Japanese education as well.