Abstract
As vagueness is one of the intrinsic features of human language, vague language exists widely in daily communication. Since vagueness was proposed in 1965, people have done much systematic and descriptive study on vague language, especially from semantic angle. However, little study from pragmatic angle has been made. In recent years, many scholars have studied vague language from linguistic aspect, but fewer have tried to carry through study on vagueness in political speeches at home and abroad, not to say in the setting of Obama’s presidential campaign speeches. Due to the above aspects, by introducing some basic notions relative to vague language and its theory, the author tries to analyze vague language from different perspectives in Obama’s presidential campaign speeches, and expound its pragmatic functions. The analysis of the examples reveals that in Obama’s presidential campaign speeches, Obama deliberately use a lot of vague language for difference purposes: to be polite, to be accurate and to be flexible.
Keywords   vague language   Obama’s campaign speech   cooperative principle   politeness principle  pragmatic function

模糊性是人类语言的本质属性之一，因而模糊语言广泛存在于日常交际之中。模糊语言自提出后的几十年里，人们对其进行了系统的描述性研究，尤其是在语义学方面，但在语用学方面的研究所见不多。近几年来，有些学者开始将模糊语言与政治演讲相结合，从而分析其功能和应用，但是很少有人从合作原则与礼貌原则理论的角度来分析奥巴马竞选总统系列演说这个具体的政治演讲领域中的模糊语言的功能与应用。鉴于此，本文通过介绍与模糊语言相关的一些基本概念及其理论，从不同层面，对奥巴马竞选总统系列演说中的模糊语言及其语用功能进行了较为系统的分析。通过研究发现，在总统竞选演讲中，奥巴马出于不同目的，有意的使用了许多模糊语言。这些目的包括：使其演讲更具礼貌性；使其演讲词更加准确；使其演讲更加灵活。
关键词  模糊语言   奥巴马演讲   合作原则   礼貌原则   语用功能

1 Introduction
As is well known, vague language is widely used in our daily communication. Since vagueness was proposed in 1965, people have done much systematic and descriptive study on vague language, especially from semantic angle. However, little study from pragmatic angle has been made. In recent years, many scholars have studied vague language from linguistic aspect, but fewer have tried to carry through study on vagueness in political speeches at home and abroad, not to say in the setting of Obama’s presidential campaign speeches. Due to the above aspects, by introducing some basic notions relative to vague language and its theory, the author tries to analyze vague language from different perspectives in Obama’s presidential campaign speeches, and expound its pragmatic functions.