本文意在阐述“ことだ”的语气特征及其语义结构。作者通过对5639个例句的分析,进一步总结了“ことだ”的意义用法,验证了“ことだ”涉及评价性语气、说明性语气、“劝诱、祈使”三个语气范畴。文章围绕着“ことだ”涉及的三个语气范畴,从思考过程的角度分析了各个范畴的意义形成过程。在此基础上,整理归纳出“ことだ”的语义结构。 This article is intended to illustrate the tone features and semantic structure of “ko da da”. Through the analysis of 5639 examples, the author further summarizes the meaning and usage of “ko da ” and verifies that “ko da ” involves the tone of assessment, explanatory tone, “persuasion, pray category. The essay focuses on the three categories of tone involved in ”Kado“ and analyzes the formation of meaning of each category from the perspective of thinking process. On this basis, we conclude the semantic structure of ”ko da ".