Root modal uses of should, ought to and be supposed to in present-day English : from patterns and profiles to proficiency guidelines
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English studies : a journal of English language and literature - ISSN 0013-838X-96:5 (2015) p. 562-595
Source and strength of modality : an empirical study of root should, ought to and be supposed to in Present-day British English
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Journal of pragmatics: an interdisciplinary quarterly of language studies - ISSN 0378-2166-55 (2013) p. 210-225