3Aarts, J. & S. Granger. 1998, Tag sequences in learner corpora: A key to interlanguage grammar and discourse [A]. In S. Granger (ed.). Learner English on Computer [C], London: Longman. 132-142.
4Aijmer, K. 2002. Modality in advanced Swedish learners' written interlanguage [A]. In S. Granger, J. Hung&S. Petch-Tyson(eds. ). Computer Learner Corpora, Second Language Acquisition and Foreign Language Teaching [C]. Amsterdam: John Benjamins. 55-76.
5Biber, D., S. Johansson, G, Leech, S. Conrad &E. Finegan. 1999. Longman Grammar of Spoken and Written English [M]. Harlow: Longman.
6Bybee, J. & S. Fleischman. 1995, Modality in grammar and discourse.. An introductory essay [A]. In J. Bybee & S. Fleischman (eds,). Modality in Grammar and Discourse [C]. Amsterdam: John Benjamins, 1-14.
7Coates, J. 1983. The Semantics of the Modal Auxiliaries [M]. London: Croom Helm.
8de Haan, F. 1997. The Interaction of Modality and Negation : A Typological Study [M]. New York: Garland.
9Gabrielatos, C. & T. McEnery. 2005. Epistemic modality in MA dissertations [OL]. http://eprints, lancs, ac. uk. 89/(accessed 30/07/2006).
10Guo, X. 2005. Modal auxiliaries in phraseology: A contrastive study of learner English and NS English [R]. Paper pre-sented at Corpus Linguistics 2005, Birmingham University, UK, July 2005.
