Akhlaghi, F. (2007). bayestan, shodan, and tavanestan: Three modal verbs in modern Persian. Dastoor, 3, 133-182 [In Persian].
Amouzadeh, M., & Rezaee, H. (2010). The semantic aspects of bayad in Persian language. Journal of Language Research, 1, 57-78 [In Persian].
Ilkhanipoor, N., & Karimi Doostan, Gh. (2016). Lexicalization of semantic dimensions of modality in Persian modal adjectives. Journal of Language Research (Zabanpazhuhi), 19, 65-87 [In Persian].
Bateni, M. R. (1969). Description of the grammatical structure of Persian language. Tehran: Amir Kabir [In Persian].
Bateni, M. R. (1975). Modern linguistic issues (ten papers). Tehran: Agah [In Persian].
Brennan, V. (1993). Root and epistemic modal auxiliary verbs (PhD thesis). University of Massachusetts, Amherst, USA.
Bybee, J., & Fleischman, S. (1995). Modality in grammar and discourse: an introductory essay. In J. L. Bybee & S. Fleischman (Eds.), Modality in Grammar and Discourse (pp. 1-14), Amesterdam: John Benjamins Publishing.
Carston, R. (2009). The explicit/implicit distinction in pragmatics and the limits of explicit communication. Pragmatics, 1(1), 35-62.
Coates, J. (1983). The semantics of the modal auxiliaries. London: Groom Helm.
Collins, P. (2007). Can/could and may/might in British, American and Australian English: A corpus‐based account. World Englishes, 26 (4), 474-491.
Depraetere, I., & Reed, S. (2006). Mood and modality in English. In B. Aarts & McMahon (Eds.), The handbook of English linguistics (pp. 269-290). Hoboken: Blackwell Publishing Ltd.
Depraetere, I., & Reed, S. (2011). Towards a more explicit taxonomy of root possibility.English Language and Linguistics, 15 (1), 1-29.
Depraetere, I. (2014). Modals and lexically saturated saturation. Journal of Pragmatics,71, 160-177.
Facchinetti, R. (2002). Can and could in contemporary British English: a study of the ICE-GB corpus. In P. Peters, P. Collins, & A. Smith (Eds.), New Frontiers of Corpus Research. Papers from the Twenty-first International Conference on English Language Research on Computerized Corpora Sydney 2000 (pp. 229-246). Amsterdam/New York: Rodopi.
Farrokhpey, M. (1979). A syntactic and semantic study of auxiliaries and modals in modern Persian (PhD thesis), University of Colorado, Boulder, USA.
Givon, T. (1995). Functionalism and grammar. Amsterdam: John Benjamins.
Gholamalizadeh, Kh. (1995). The structure of Persian language. Tehran: Ehya’e Ketab [In Persian].
Goossens, L. (1985). Modality and the modals. In M. Bolkestein, C. De Groot & L. Mackenzie (Eds.), Predicates and Terms in Functional Grammar (pp. 203–217). Dordrecht: Foris.
Halliday, M. A. (1970). Functional diversity in language as seen from a consideration of modality and mood in English. Foundations of Language, 322-361.
Hengeveld, K. (1989). Layers and operators in functional grammar. Journal of Linguistics, 25 (1), 127-157.
Homayoonfar, M. (2013). Investigating the grammaticalization process of Persian modals based on Leman’s parameters, Dastoor, 9, 50-73 [In Persian].
Huddleston, R., & Pullum, G. K. (2002). The Cambridge grammar of English language.Cambridge: Cambridge University Press.
Huitink, J. (2012). Modal concord: A case study of Dutch. Journal of semantics, 29 (3), 403-437.
Kratzer, A. (1977). What ‘must’ and ‘can’ must and can mean. Linguistics and philosophy, 1 (3), 337-355.
Kratzer, A. (1991). Modality. In A. von Stechow & D. Wunderlich (Eds.), Semantics: an international handbook of contemporary research (pp. 639-650). Berlin: de Gruyter.
Kratzer, A. (2012) Modals and conditionals: New and revised perspectives (Vol. 36). Oxford: Oxford University Press.
Lyons, J. (1977). Semantics. Cambridge: Cambridge University Press.
Lyons, J. (1995). Linguistic semantics: An introduction. Cambridge: Cambridge University Press.
Mashkut-al-dini, M. (2000). Persian grammar based on transformational theory. Mashhad: Mashhad University Press [In Persian].
Palmer, F. R. (1987). The English verb. London and New York: Longman.
Palmer, F. R. (1986). Mood and modality. Cambridge: Cambridge University Press.
Palmer, F. R. (2001). Mood and modality (2nd ed). Cambridge: Cambridge University Press.
Palmer, F. R. (1990). Modality and the English modals. London: Longman.
Papafragou, A. (2000). Modality: Issues in the semantics-pragmatics interface. Amesterdom: Elsevier.
Portner, P. (2009). Modality. Oxford: Oxford University Press.
Rahimian, J. (2009). The formal and semantic aspects of Persian modal elements in modalized sentences. Journal of Linguistics & Khorasan Dialects, 1, 75-91 [In Persian].
Rahimian, J., & Amouzadeh, M. (2013). Modal auxiliaries in Persian and expression of modality. Journal of Language Research, 4 (1), 20-40 [In Persian].
Recanati, F. (2004). Literal meaning. Cambridge: Cambridge University Press.
Salkie, R. (2009). Degrees of modality. In R. Salkie, P. Busuttil & J. Van der Auwera (Eds.), Modality in English: Theory and description (Vol. 58, pp. 79-103). Berlin: Walter de Gruyter.
Taleghani, A. H. (2008). Modality, aspect and negation in Persian (Vol. 128). Amesterdam: John Benjamins Publishing.
Traugott, E. G., & Konig, E. (1991). The semantics pragmatics of grammaticalization revisited. In E. C. Traugott & B. Heine (Eds.), Approaches to Grammaticalization (2nd Vol., pp.189-218). Amesterdam: John Benjamins Publishing.
Van Der Auwera, J. & Plungian, V. (1998). Modality’s semantic map. Linguistic Typology, 2, 79–124.
Van Der Auwera, J. & Ammann, A. (2008). Overlap between situational and epistemic modal marking. In M. Haspelmath, M. S. Dryer, D. Gil, & B. Comrie
With the collaboration of H. Bibiko, H. Jung, and C. Schmidt (Eds.), The World Atlas of language structures, (pp. 310-313). Oxford: Oxford University Press.