Vocabulary is the most unstable part of the language, it is constantly undergoing changes in form and meaning. Just as Quirk said in 1963,“almost every word we use today has a

    different meaning from the one it had a century ago, and a century ago it had a slight different meaning from the one it had a century before that”. As we all known, the semantic change has gone through a very long history. So, there is no doubt that there are many kinds of semantic change. The change of the meaning of the word is divided into two kinds: meaning development and meaning shift. There are many kinds of the evolution of the meaning, the influence of the meaning evolution is also varied.

    The reasons in the evolution of the meaning is varied, in general is influenced by linguistic and extra-linguistic. The reasons of the linguistic has many factors. The changes in word meaning is associated with the development of the language itself, and the development of language is closely related to people's cognitive ability raise. Language was originally

    specific perception of things, a word indicating a specific things. Such as book is the ancient Germanic alphabet, gradually book is the group of similar phenomena. As the

    development of the people’s cognitive ability, the concept of

the book is also expanding. Book is a book of literary works,

    is the knowledge and understanding of things, is a kind of record. So,the meaning of the book has a great changes today.

    Loanwords in English much more special, the influence of loanwords has also led to the changes of word meaning. Because

    of loanwords can more accurately describe something, so that some of the native language has lost the original meaning. Or due to the introduction of loanwords, the meaning of the original English words have changed. The aim is to make the different. Such as stool original meaning is refer to kinds of seat. Later, due to the imported chair from France to show more comfortable seats, stool?meaning become bench. Another typical example is the pig, cow and sheep in the English original meaning is refer themselves, and now their meaning also refer their meat. A change increase or decrease will cause about the meaning of the meaning of words. “tide” is refer “time”

    “season” “hour”, but later it produced “time” “season”

    “hour” to replace “tide”. So, the meaning of the tide is

    reduced. Simplified also tend to cause the meaning of word meaning evolution. The uniform is simplified from the uniform dress. Duplicate is simplified from the duplicate copy. Daily is simplified from the newspaper. The analogy, metaphor, and

    metonymy in the language also lead the word evolved. Fox was, constantly is used metaphorically as cunning as a fox. The causes of semantic evolution is not only the internal reason, but also the social reason. First, the development of the society is important. Non-linguistic factors is mainly refers to history or influence on the development of the society. With

    the development of society and human knowledge, people for the social things, concepts, ideas change constantly, therefore reflect the objective things or phenomena tend to change the meaning of words. The car originally refers to two rounds of chariots, now people will be car as the main transport. Has

    pointed out the fundamental changes have taken place in the Car, but the name does not change. Professional terms and common vocabulary between cross use, often also makes the meaning of the word evolved. For example, the salt into all salts in the chemical term. Some words of sports with the development of sports.

    Social events will often make the change the meaning of the word. Impeachment ?meaning is national civil servants of crime control. Especially in the United States, can be the President's impeachment. Major English speaking countries political environment in Britain and the United States is

    slightly different, also have differences in vocabulary. Britain's head of state is a monarch, the others are all his subjects, but the head of state is a President of the United States.

    The psychological factors of social life and has caused the evolution of the meaning of praise or blame. In the meaning of the development process, we can found that the language belongs to the winners. The class which has the power, the class which has the right to define the meaning of. In the semantic change, the people who are related to low social status, such as villain, knave and churl.

    The affection between people will also affect it's praise or blame. Some bad thing with the name of the other ethnic groups, as if something bad was done by the others. British people to do all these things are foreigners with bad. For example, to take French leave.

    Ethnic emotion mainly on discrimination for colored people in the United States now. “a Black” is the black slander. And

    there are in the vocabulary of English language of gender discrimination.

    Social values affect meaning, the most interesting example is the euphemism.