1. Abdi, R. (2002). Interpersonal metadiscourse: An indicator of interaction and identity. Discourse Studies, 4(2), 139-145.
2. Brown, P. & Levinson, S.C. (1987). Politeness: Some Universals in Language Usage (Vol.4). Cambridge University Press.
3. Bybee, J. (1995). The semantic development of past tense modals in English.Modality in grammar and discourse, 503-517.
4. Fu, X., & Hyland, K. (2014). Interaction in two journalistic genres: A study of interactional metadiscourse. English Text Construction, 7(1), 122-144.
5. Garcia, F.G. (2000). Modulating Grammar through Modality: a discourse approach. Elia Estudios de linguistica inglesa aplicada, (1), 119-134.
6. Ghazzoul, N. (2019). Linguistic and pragmatic failure of Arab learners in direct polite requests and invitations: A cross-cultural study. Theory and Practice in Language Studies, 9(2), 223-230.
7. Govindasamy, S. (2002). The Use of English Epistemic Modality Among ESL Learners. Jurnal Bahasa Moden. Universiti Malaya. Keluaran 14, September 2002.
8. Hacquard, V., & Wellwood, A. (2012). Embedding epistemic modals in English: A corpus-based study. Semantics and Pragmatics, 5(4), 1-29.
9. Hashemi, M.R., & Shirazdi, D. (2016). The Use of Hedging in Discussion Sections of Applied Linguistics Research Articles with Varied Research Methods. Journal of Teaching Language Skills, 35 (1), 31-56.
10. He, M., & Rahim, H. A. (2019). Comparing Engagement Markers in Economics Research Articles and Opinion Pieces: A Corpus-based Study. GEMA Online Journal of Language Studies, 19(2).
11. Huffman, A. (1989.) The System of Probability: A brief overview and preliminary statement of its application to the teaching of English. Unpublished Manuscript. New York: Columbia University.
12. Hyland, K. (1998). Boosting, hedging and the negotiation of academic knowledge. Text, 18, 349–382.
13. Hyland, K. (2000). Hedges, boosters and lexical invisibility: Noticing modifiers in academic texts. Language Awareness, 9(4), 179-197.
14. Hyland, K. (2001). Metadiscourse: Mapping interactions in academic writing. Nordic Journal of English Studies, 9(2), 125-143.
15. Hyland, K. (2005). Metadiscourse: Exploring Interaction in Writing. London: Continuum.
16. Hyland, K. (2008). Genre and academic writing in the disciplines. Language Teaching, 41(04), 543-562.
17. Hyland, K. (2010). Constructing Proximity : Relating to readers in popular and professional science. Journal of English for Academic Purposes, 9(2), 116-127.
18. Hyland, K. (2015). Genre, discipline and identity. Journal of English for Academic Purposes, 19, 32-43.
19. Lakoff, G. (1973). Hedges: A study in meaning criteria and the logic of fuzzy concepts Journal of Philosophical Logic, 2, 458-508
20. Lewis, M. (2002a). The English Verb – An Exploration of Structure and Meaning. Boston : Heinle.
21. Lewis, M. (2002b). The Lexical Approach – The State of ELT and a Way Forward.Boston : Heinle.
22. Lock, G. (1996). Functional English Grammar – An Introduction for Second Language Teachers. New York: Cambridge University.
23. Loi, C. K., & Lim, J. M. H. (2019). Hedging in the Discussion Sections of English and Malay Educational Research Articles. GEMA Online Journal of Language Studies, 19(1).
24. Mei, H. C., & Shuib, M. (2014). An analysis of hedging devices in complaint business letters. Journal of Language Studies, 14(3), 123-142.
25. Noorian, M., & Biria, R. (2010). Interpersonal metadiscourse in persuasive journalism: A study of texts by American and Iranian EFL columnists. Journal of Modern Languages, 20(1), 64-79.
26. Palmer, F.R. (2007). Mood and Modality. Beijing: World Book Publishing Company.
27. Salkie, R. (2010). Will: tense or modal or both? English Language and Linguistics, 14(02), 187-215.
28. Stern, N. (2016). Word order as a signal of meaning: English reflexive pronouns and why we behave ourselves. In Leanne Rolston (Ed.), University of Washington Working Papers in Linguistics (pp. 111-119). https://depts.washington.edu/uwwpl/editions/vol34.html
29. Takimoto, M. (2015). A corpus-based analysis of hedges and boosters in English academic articles. Indonesian Journal of Applied Linguistics, 5 (1), 95 – 105.
30. Vazquez Orta, I. & Giner, D. (2009.) Writing with conviction: The use of boosters in modelling persuasion in academic discourses. Revista Alicantina de Estudios Inglesses 22, 219-237.
31. Wang, S. P., & Tatiana, K. (2016). Corpus research on hedges in linguistics and EFL journal papers. International Journal of Education, 9(1), 45-52.
32. Ward, G., Birner, B.J. & Kaplan, J.P. (2003). A Pragmatic analysis of the epistemic would construction in English. In Palmer, F., Krug, M. & Facchinetti, R. (eds.) Modality in Contemporary English. New York: Mouton de Gruyter.
33. Whitty, L. (2019). An Investigation of Learners’ Use of CAN and COULD in an English Language Classroom. Australian Journal of Applied Linguistics, 2 (1), 32 – 46.
34. Yagız, O., & Demir, C. (2015). Hedging strategies in academic discourse: A comparative analysis of Turkish writers and native writers of English. Procedia-Social and Behavioral Sciences, 158, 260-268.