Williams (1981) labels metadiscourse as a stylistic variable and it is a very important part in writing. Williams also classifies two levels in the communication between writer and reader. The first level is the primary discourse which supplies information and expands content; the second one is the level of metadiscourse which guides readers to organize, interpret, evaluate and react to the content. He classifies metadiscourse broadly as three categories: hedges and emphatics, sequencers and topicalizers, attributors and narrators.

Crismore (1983) considers that metadiscourse has two functions. On the one hand, metadiscourse directs the readers how to understand the writer’s purpose and the primary message by its content and structure. On the other hand, it also directs the readers how to understand the writer’s perspective or structure of the primary discourse. She identifies two general categories which are informational metadiscourse and attitudinal metadiscourse.

Based on Lautamatti’s and Williams’ classification, Vande Kopple (1985) identifies metadiscourse as two major categories: textual and interpersonal metadiscourse. Later, many scholars, such as Crismore (1989), Markkanen and Steffensen (1993), make studies in this field based on William’s research.

Hyland (1994) classifies metadiscourse as textual metadiscourse and interpersonal discourse. When he uses the classification in his study, he meets some issues. Then, Hyland (2004), together with Tse, puts forward a more specified classification. Then Hyland develops the concepts of interactive and interactional resources noted by Thompson (2001).

2.3 Hyland and Tse’s Model
Hyland and Tse (2004) analyzed postgraduate dissertations counting up to four million words, and produced a model of metadiscourse. Through this research, they reclassify metadiscourse as two main categories as follows.

Interactive resources are concerned with how to organize discourse to take reader’s knowledge into consideration and reflect the writer’s intention to guide reader through the text. They consist of five sub-categories:
1)    Transitions are used to express the semantic relation between main clauses.
2)    Frame markers indicate text boundaries or elements of schematic text structure or items used to sequence, to label text stages, to announce discourse goals, and to indicate topic shifts.
3)    Endophoric markers refer to information in other parts of the texts and help readers understand writer’s meanings and intentions.
4)    Evidentials refer to information from other texts.
5)    Code glosses explain and restate propositional meanings in another way to make sure that readers get the writer’s intentions.

Interactional resources focus on showing the writer’s personal views and establishing a suitable relationship with reader to convey attitude to him. This is a way to express writer’s comments and emphasize on writer’s effort to control the text. Five sub-categories of this category are as follows:
1) Hedges indicate the writer’s degree of commitment to the proposition and viewpoints. It does not emphasize on the fact, but opinions that are allowed to form.
2) Boosters emphasize on the certainty of statements and make a conclusion. It plays an important role in conveying commitment to the text.
3) Attitude markers express the writer’s attitude towards propositions. It is an expression to convey how the writer feels.
4) Engagement markers focus on the reader’s attention and consider them as participants.
5) Self-mentions reflect the extent of author presence in terms of first person pronouns and possessives. 《傲慢与偏见》小说与电视剧的元话语运用比较(4):http://www.youerw.com/yingyu/lunwen_7971.html