Abstract:Languages are not confined in a fixed state, instead, they are constanly changing with the development of human society and technology. The most noticing change in the porcess of language development is the sematic change of words. Since in human beings evolution, we need to continuously explore the unknown terretoties to form new ideas and opinions. A large number of new words are needed to describe new things, and hence to promote communication, in orde to reach effective interaction. As we know, the basic unit in language system-vocabularies and their meanings are changing, so the changes of English semantics are caused by many reasons. Here the paper will focus on such points as the historical cause, social cause, linguistic cause, foreign cause and psychologiacal cause. Hence, the clear study of the causes can be beneficail and useful for the English learners to have a better understanding of English vocabulary and use English porperly. 

Key words: English semantic change; historical cause; social cause; linguistic cause; foreign influence; psychologiacal cause

中文摘要:语言从未囿于固定不变的封闭状态，而是经常处在变化之中。语言的发展变化最引人注目的是词汇的变化，这是因为在人类社会的发展进程中，人们不断地探究到新的东西，形成新的观点和思想，语言在服务于交际的过程中，需要大量的新词新义来描述这些新的事物，以达到有效促进人们沟通了解，顺利实现交际的目的。语言系统的一个基本单位——词汇也一样。引起英语词义变化的原因有很多，在此我们讨论社会，历史，语言，外来语影响，心理等原因。明晰英语词义变化的原因和方式，将有助于学习者全面了解词义，并获得与词义变化相关的文化知识，促进英语学习。

关键词：英语词义演变；历史原因；社会原因；语言原因；外来语影响；心理原因