预设是S和S的否定式都能够推导出来的语句，也可以说是交际双方共有的背景命题。本文试图通过对预设与断言，预设与蕴含这两组概念的讨论，分析汉语预设的若干情形，进而探讨析出预设的逻辑方法以及预设在语言交流中的作用。预设与断言是两个相近而又有区别的概念。预设同断言 The presupposition is that the negation of S and S can be derived from the statement, which can also be said to be the common background proposition of both parties in communication. This paper tries to analyze several situations of Chinese presupposition by discussing the concepts of presupposition, assertion, presupposition and implication, and then explore the preconceived logic method and the role of presupposition in language exchange. Presets and assertions are two similar and different concepts. Default with the assertion