Nash once mentioned, “The word ‘metadiscourse’ may have a reassuringly objective, ‘scientific’ ring, but its usage suggests boundaries of definition no more firmly drawn than those of, say, ‘rhetoric’ or ‘style’. One reader may perceive a clear stylistic intention in something which another reader dismisses as a commonplace, ‘automatized’ use of language.” (1992:100)

According to Hyland (2000), metadiscourse offers a framework for understanding communication as social engagement. It illuminates some aspects of how the author projects himself into the discourses by signaling his attitude towards both the content and the audience of the text. With the judicious addition of metadiscourse, a writer is able not only to transform what might otherwise be a dry or difficult text into coherent, reader-friendly prose, but also to relate it to a given context and convey his or her personality, credibility, audience-sensitivity to the message. Using a contrastive corpus of American sitcoms in different times, this study seeks to identify whether the use of metadiscourse has changed or not in the past decades. Disclosing the changes of using metadiscourse in American sitcoms, if it has any changes, and finding out what kind of changes they have undergone will shed new light on the evolution of metadiscourse in American sitcoms.

Based on a historical linguistic perspective, the study chooses two famous American sitcoms, The Big Bang Theory and Growing Pains as research material because these two TV series are the representatives of English-language classical American sitcoms which span more than two decades. The span is wide enough to allow a clear picture of the changes of metadiscourse, if any. Another reason for choosing the two sitcoms is that both of them enjoy wide popularity in different times. Through the research of metadiscourse categories predominating in this type of American sitcoms, the study will expose how different roles project their thoughts and attitudes toward the scripts by using metadiscourse. And by comparing the two sitcoms, the historical changes of metadiscourse will be brought to light.

The focus of this study is to examine metadiscourse categories used in these two American sitcoms and to identify the similarities and differences between them. Moreover, the study is also intended to stress the need for more contrastive studies in the area of metadiscourse and more attention to this important element in scripts as well as other fields.

2 Metadiscourse
The term metadiscourse was first coined by Zellig Harris in 1959, it has gained increasing interest in a variety of research fields in recent years as a relatively new concept in discourse analysis. Metadiscourse offers a way of understanding in use, expressing a writer’s or speaker’s thoughts to guide a receiver’s standpoint of a text. The concept has been further developed by the writers we have known about, such as Williams (1981), Vande Kopple (1985) and Crismore (1989).

Metadiscourse includes the idea that communication is more than just the exchange of information, goods or services between interlocutors, but also contains the attitudes, personalities and assumptions of those people who are communicating. We can consider language as a consequence of interaction, of the differences between people which are expressed vocally, and metadiscourse options are the ways we verbalize and create these interactions.

2.1 Definitions and Issues
The definition of metadiscourse has been put forward from various angles. Crismore (1984a) records that metadiscourse can be defined both narrowly and broadly according to the field which scholars are working in, such as semiotics, philosophy, speech communication, rhetoric and linguistics. Semioticians, philosophers, speech communication theorists, and rhetoricians define metadiscourse broadly while linguists define it narrowly. 《生活大爆炸》与《成长烦恼》元话语运用比较(2):http://www.youerw.com/yingyu/lunwen_3844.html