Various cohesive devices of discourse are complementary to each other。 They play the role of a cohesive connection together。 Cohesion, as one of the necessary conditions, is very important for the understanding of a text。 Discourse is not a simple accumulation of unrelated sentences, but some meaning associated sentences to achieve certain communicative purpose, realize the organic combination through various cohesive devices。

Among them, lexical cohesion is one important aspect。 Vocabulary is a basic element of discourse。 However, discourse is not an arbitrary pyramiding of vocabulary。 As an important approach of cohesion, lexical cohesion adopts some methods to realize semantic connections in discourse。 Obviously It is of great importance to the speech for that a coherent speech better conveys the speaker’s thoughts and achieve better effects。 So cohesion is an indispensable element to a pragmatic public speech。

Based on the cohesion theory by Halliday & Hasan, this thesis analyses the application of lexical cohesion approaches in public speech from the perspectives of personal pronouns, reiteration, synonymy, antonym, rhetorical devices and the selection of formal and casual language。 The writer will use some concrete examples to better explain respective functions of these devices in improving the quality of public speeches, and to illustrate that the combination of these devices can help make the speech more vivid, impressive, persuasive and coherent。来*自~优|尔^论:文+网www.youerw.com +QQ752018766*

2。 Literature Review

In the 1960s and 1970s, experts became aware of grammatical relations which could be gained through sentence boundaries and began to show interest in discourse structure。 After the publication of the book A Grammar of Contemporary English written by Randolph Quirk in 1972, studies on discourse have started。 Jacobson is a pioneer who studies cohesion。 In 1968, Hasan published her book Grammatical Cohesion in Spoken and Written English, in which she gives a detailed description of cohesion。 She indicates that to achieve cohesion, one has to find the typical characteristics of a text and pides between a group of meaningless sentences and a text。 In 2001, M。A。K。Halliday and Hasan published Cohesion in English, which marks the foundation of cohesion theory。 The results of these studies on cohesion and coherence have provided meaningful implication for the composition of a successful speech。

2。1 Cohesion

The earlier linguistics regards cohesion as the degree of connection between two or more morphemes。 For example, the relationship between “quiet” and “ly” is closer than that between “father” and “mother”。 After that, cohesion is considered as the relationship between linguistic units larger than a word。