Humor, as a special effect of language, has long been the subject of study for linguists, psychologists and sociologists alike. Meanwhile, a series of humor theories have been put forward, among which are the Superiority Theory, the Release Theory, the Incongruity Theory, the Semantic Script Theory and the General Theory of Verbal Humor. In western societies, the study on humors has always been an interest field for many scholars. For instance, in the classical Greek times, many scholars investigated humors, such as Plato and Aristotle. They developed one of the most important theories of humors, the Superiority Theory. The humor is present through out social conventions and cultural spread, and the use of humor is highly valued in interactions between people. Therefore humor is a hot and complicated topic to study.
Conversational humor, that is, humor produced via the exchange of utterances between speakers and listeners, has been the focus of language researchers for a long time. As a language learner, it is very important to have the ability to understand and enjoy conversational humor or to interpret what is implied by the speaker in a certain way, which is considered to be an essential part of the learner’s language competence. Since language competence is rather a difficult ability to acquire for language learners, partly due to the language barrier, partly due to a lack of situational context, it is a tough job for teachers of foreign languages to instruct their students to appreciate conversational humor. Fortunately in recent years, as advocated by Professor Hu Wenzhong (1989), more and more attention has been paid to teaching foreign languages through films and TV plays. Norrick takes the initiative in studying everyday talk in his work Conversational Joking: Humor in Everyday Talk, which turns the research orientation to spontaneous humor rather than canned jokes; and Nash’s The Language of Humor: Style and Techniques in Comic Discourse has inspired some tentative research toward the analysis of the linguistic features of conversational humor. Recently, along with the development of linguistics, humor has been of great concern to linguists. This is a very natural trend, for any jokes (including other genres), by its very nature of verbalization, necessarily play upon language. (Chiaro 15)

II. The Definition, Classification and Function of Humor

2.1 The Definition of Humor
Humor can be found almost everywhere. It has permeated every sphere and aspect of humans’ lives. It is seen to involve adjustment, happiness, hope, intelligence, joy, and love. Not only does humor have significant uses in the various disciplines and in our personal lives, but it also makes life worth living. If we are attentive to our actual behavior, look and see what we actually value and experience, we will observe that humor is often the most important thing in our lives. For centuries, humor has always been a hot topic that attracts interests and attention of researchers in various fields from psychology to sociology. There are many theories of humor which attempt to explain what humor is, what social function it serves, and what would be considered humorous. Though many studies have been conducted on humor, it is still a concept rather elusive and indefinable. It is rather difficult to define humor exactly because everyone has his sense of humor, and the ways of creating humor are various too. As William Congreve (1695) says, “to definite humor is difficult for it is of infinite variety” (Palmer 39). The nature of humor also varies considerably from culture to culture. Linguists, rhetoricians, sociologists, psychologists, philosophers and anthropologists have conducted many effective researches to reveal the nature of humor. 美国情景喜剧《成长的烦恼》中言语幽默解析(2):http://www.youerw.com/yingyu/lunwen_18328.html