Abstract：
All languages in the world change constantly except those dead languages like Latin. As an important aspect of language learning, word meaning changes too over the course of centuries, although it seems stable within a certain period of time. English is now one of the most significant world languages, which had gone through many semantic change periods, namely, Old English period, Middle English period and Modern English period. With the influence of vocabularies of French, Latin, Greek and Scandinavian, the English vocabularies have been greatly enriched and their meanings changed simultaneously.
In the course of studying semantic change, this paper will analyses four major meaning shift tendencies with two change patterns, and it will explore four major causes of meaning change. Actually, linguists from home and abroad have found out many change tendencies, like extension, narrowing, degradation, elevation, metaphor, metonymy, synecdoche, transference, euphemism and so on, however, this paper will only chose a few change tendencies which are by far the most common. From those change tendencies, it’s not difficult to come into conclusion that there are two change patterns in total, radiation and concatenation. At the last part, the author would analyse the reasons of change from four aspects, foreign influences, linguistic factors, social causes and psychological reason.
Apparently, to make the process of semantic change clear is also to make the history and culture clear. During the English learning procedure, it will help the learner to get a comprehensive understanding of the language, if they study the word meaning and its change process from diachronic perspective.

Key words：word meaning; semantic change; elevation; degradation

摘  要：
世界上所有的语言，除了像拉丁语那样已经死掉的语言，都在不断地变化。词汇的意义作为语言的重要组成部分，虽然在某一个特定的时期看起来不变，几个世纪以来也在不断变化。如今，英语成为世界是最重要的语言之一，它经历了古英语时期，中世纪英语时期和现代英语时期三个主要的变化阶段。在法语，拉丁语，希腊语和斯堪的纳维亚语的影响下，英语的词汇被大大的扩充，其意义也随之发生了巨大的变化。
在学习词义变化的过程中，本文将阐释两大变化方式，四大变化趋势及四大变化原因。实际上，国内外的语言学家已经总结出来许多的变化趋势，如扩大，缩小，降格，升格，隐喻，转喻，提喻，转换，委婉语等，但是本文只会选择几个较为常用的进行分析。通过那些变化趋势，不难推断出总共有两个变化方式，辐射性和连锁型。在最后的部分，笔者将从四个方面分析变化的原因，即外来语的影响，语言因素，社会因素和心理因素。
很显然，弄清词义变化的过程也是弄清历史和文化的过程。在英语学习过程中，只要从历时的角度学习词汇意义及它的变化，就会对英语有一个全面的认识。

关键词：词义；词义变化；升华；降格