This thesis consists of five parts, with the introduction of Chapter one, the background of the research, the objective and significance of the study, the purpose of this paper and the overall structure of the thesis. Chapter two will give the introduction to humor and Situation Comedy, and offers the overview of the Cooperative Principle, which include the introduction of the theory of Cooperative Principle and the four maxims of the CP. Chapter three will present some cases in the Friends with the violation of the four maxims, then there comes the main finding and analysis of humor effect which is produced by them. Chapter four will present the implications of this study as well as suggestions for future research. It will also talk about the application of humor in English teaching, which include create active class atmosphere, develop a harmonious relationship between students and teacher, light students’ spirit and desire of learning, and optimize students’ characters. The last part of this thesis is the conclusion which gives a summary of this paper.

II. Background Information

2.1 Introduction to Humor
Humor gives people great pleasure in daily communication, and gains its popularity in many spheres of life. Scholars in the fields of psychology, anthropology, philosophy, as well as linguistics have achieved great success in the process of humor study. Although it is of great importance in daily life, an agreed and satisfactory definition of humor has not been put forward. Many scholars are still indulging themselves in studying this complicated phenomenon. The present study aims at providing a thorough explanation about how humorous effects are achieved through analyzing the humorous conversations appeared in the sitcom Friends, In order to make the study of verbal humor convincing and credible, a general and complete description of humor will be provided first by the author.
The word “humor” and the humorous phenomena are frequently appeared in daily life. Before we analyze the verbal humor in Friends, a preliminary step is to make it clear what is humor. Researches on humor can be dated to the time of Aristotle, while the definition of humor varies from person to person. A large number of humor researchers mean to define humor in a proper way which can provide a reflection to the nature of humor but a consensus has never been reached.
From the perspective of etymology, the Latin word “humere” is believed to be the origin of the English word "humor", which conveys such meaning as “liquid” or “fluid” in the humoral medicine of the ancient Greeks. From the statements made by ancient Physicians, it is apparent that people’s character and temperament are determined by four human body fluids. If these fluids are in balance, then a person can be said to be "well-humored". However, as time goes by, the original explanations of humor gradually disappear and it comes to refer to the mood and quality of a person, which is easier to understand than its traditional meaning, but a more satisfactory definition is still hard to provide. Various definitions have been put forward by different scholars during their researching process.
Sigmnd Freud has made a great contribution to the study of humor, he Consider humor as a useful way of getting access to happiness regardless of the interference of bad mood, and it is "a window into the unconscious" (67). It seems that the amusement of humor comes from the release of pressure or depression.
Humor was introduced into China by the famous Chinese scholar Lin Yutang in the early 20th century. He is also the first man who translate “humor” into 幽默 in Chinese, and defines humor as “ a tone, a mind style, and category of discourse" (2) and “style of writing, which can exhibit itself under any topic as long as the humorist is in tune with the mood" (7-8). 合作原则视角下《老友记》中的言语幽默(2):http://www.youerw.com/yingyu/lunwen_18440.html