Table of contents Acknowledgements Table of content Abstract Abbreviations and conventions Lists of tables, chart and graphs Part A: Introduction 1. Rationale 2. Aims of the study 3. Objectives of the study 4. Scope of the study 5. Organisation of the study Part B: Development Chapter I: Literature review 1.1. Speech acts 1.1.1. The notion of speech acts 1.1.2. Classifications of speech acts 1.1.3. Illocutionary Force Indicating Devices 1.1.4. Felicity conditions 1.1.5. Expressing gratitude as a speech act 1.2. Theories of politeness 1.2.1. Brown &Levinson’s theory of politeness 1.2.2. Social factors affecting politeness in communication 1.2.3. Indirectness and politeness 1.3. Co-operative Principle 1.3.1. Non-observance of the maxims 1.3.1.1. Flouting a maxim 1.3.1.2. Violating a maxim 1.3.1.3. Infringing a maxim 1.3.1.4. Opting out a maxim 1.3.1.5. Suspending a maxim 1.4. Relevance theory Chapter II: Methodology 2.1. Research questions 2.2. Research method 2.2.1 Data collection method 2.2.2. The method of the study 2.2.2.1 Data collection instruments 2.2.2.2.1. Variables manipulated in the data collection instruments 2.2.2.2.2. The content of the questionnaires 2.2.2.2. Selection of subjects 2.2.2.4. Results of the MPQ 2.3. Analytical framework 3.6.1. Eisenstein &Bodman’s analytical framework 3.6.2. Analytical framework of the study Chapter III: Data analysis 3.1. Choice of sub acts in higher power setting (+P) 3.1.1. Choice of sub acts in sit 1 3.1.2. Choice of sub acts in sit 2 3.2. Choice of sub acts in equal power setting (=P) 3.2.1. Choice of sub acts in sit 6 3.2.2. Choice of sub acts in sit 9 3,3, Choice of sub acts in lower power setting (-P) 3.3.1. Choice of sub acts in sit11 3.3.2. Choice of sub acts in sit 12 3.4. Choice of sub acts in the setting where the degree of gratitudeis low (-R) 3.3. Choice of sub acts in the setting where the ranking of imposition is high (+R) 3.4. Conclusion Part C: Conclusion 1. Major findings 1.1. Data collection instrument 1.2. Choice of sub acts in expressing gratitude 2. Implications for teaching and learning English in Vietnam 3. Suggestions for further research APPENDIX A APPENDIX B REFERENCES