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1 Schneider, E., "Varieties of English: The Americas and the Caribbean" Mouton de Gruyter 2008
2 Mesthrie, R., "Varieties of English: Africa, South and Southeast Asia" Mouton de Gruyter 2008
3 Coates, J., "The Verb in Contemporary English: Theory and Description" Cambridge University Press 145-156, 1995
4 Ljung, M., "The Use of Modals in British and American Newspapers" 36 : 159-179, 1996
5 Coates, J., "The Semantics of the Modal Auxiliaries" Croom Helm 1983
6 Collins, P., "The Semantics of Some Modals in Contemporary Australian English" 8 : 233-258, 1988
7 Greenbaum, Sidney, "The Oxford English Grammar" Oxford University Press 1996
8 Beiler, I. R., "The Modals of Possibility and Permission in Standard English Varieties of England, Scotland, and the United States: A Study in Dialectal Variation" American University 2010
9 Tagliamonte, S., "The Modals of Obligation/Necessity in Canadian Perspective" 28 (28): 47-87, 2007
10 Coates, J., "The Meanings of the Modals in British and American English" 8 : 23-24, 1980
11 Peters, P., "The Cambridge Guide to English Usage" Cambridge University Press 2004
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35 Trudgill, P., "Dialects in Contact" Blackwell 1986
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