Abstract
Based on conceptual metaphor put forward by Lakoff, this paper takes American President Obama’s political speeches as materials and uses qualitative and quantitative methods to analyze the metaphor phenomena in political discourse. Metaphors in the selected speeches and their usage are studied and then categorized. Then detailed analysis on the three main metaphor types, namely “conflict” “journey” “building”，is further elaborated. Meanwhile this paper studies the cognitive characteristics of these conceptual metaphors to indicate the values and ideology reflected by the metaphors, and how metaphors influence people’s thought and make people respond to the appeal to take action.
Keywords   conceptual metaphor   political speech   ideology

本文以美国总统奥巴马的政治演讲为语料，以Lakoff的概念隐喻为理论，以定性定量研究结合的方法，试图对政治语篇中的隐喻现象进行分析。依据Lakoff的概念隐喻理论，本文研究了所选语篇中的隐喻及使用特点，对隐喻进行分类，并着重对其中的三大类概念隐喻模式，即“旅程”、“建筑”、“冲突”进行具体分析。同时，本文还分析了这些概念隐喻背后蕴含的认知特点，揭示概念隐喻所体现的意识形态、价值观念以及其如何影响人们的意识，使人们响应号召、采取行动。
关键词  概念隐喻   政治演讲   意识形态

1 Introduction
1.1    The Purpose of the Thesis
As early as 2000 years ago, metaphor as linguistic phenomena was well noticed by scholars. Traditionally, metaphor is viewed as a matter of language, as a set of extraordinary or figurative expressions whose meaning is confined to some set of literal propositions. In the past few decades, however, the situation has undergone a radical change. The interest in metaphor has grown rapidly in a broad range of disciplines. And this change is observed as a metaphormania. Metaphor has already moved from a subsidiary subject to a central problem. In the 1980s, metaphor became an important topic in cognitive science.
In 1980, Lakoff and Johnson published the book Metaphor We Live By. It was a turning point in metaphor study, because since then, metaphor study has a new prospective, that is cognitive prospective. The theory claims that metaphor is not only a rhetoric method, but more concerns with human cognitive mechanism. The scholars regard metaphor as conceptual mapping across the cognitive domains. Metaphor is very universal in human cognition and exists in all linguistic types.