The term modality has been originally understood as the truth value of the proposition by logicians. In linguistics, modalities are considered as the structures that in one way or another evaluate the state of affair. They "refer to aspects of meaning which cause sentences to be about the non-factual, that is, about the alternative possibilities for how things could be" (Fasold & Connor-Linton, 2006, p. 153).
As a semantic-grammatical category concerned with the "status of the proposition that describes the event" expressed by an utterance (Palmer 2007, p: 1), modality might also be construed as "the relativization of the validity of sentence meanings to a set of possible worlds" or "ways in which people could conceive the world to be different" (Kiefer, 1994, p: 2515). In other words, modality allows language users to express what is, what would be, what may be, and what should be. All languages express modality through either grammatical mood or modal systems (or both), making modality a "valid cross-language grammatical category" in need of a cross-linguistic description (Palmer, 2007, p: 1).
Modality can be both epistemic and deontic (Palmer, 2003). Epistemic modality indicates the means by which speakers/writers express judgment on the truth of the propositions they utter/write. In other words, language users use epistemic modality to make judgments about the possibility or necessity of an entire proposition (Palmer 2003: 7)
Deontic modality, on the other hand, is concerned with the criterion by which speakers/writers decide which future events are necessary, possible, desirable, etc. Deontic modality is the "expression of the judgment of possibility including permissibility or necessity including obligation of an action, state, or event by a speaker" in which control of the action, state, or event is external to the subject of the clause (Palmer, 1990, pp:50, 69-74; Palmer, 2003,p: 7). In general, deontic modality is "dependent on some kind of authority, often the speaker" (Palmer, 2007, p: 70); in order words, the ability of an event to occur comes from the permission granted by the speaker or some other authority as opposed to the subject (Palmer 2003: 7)
Referring to Halliday's overarching functions which language is said to fulfill, namely ideational, interpersonal and textual, modality operates within the interpersonal function of the language- the function through which we represent ours to others (Halliday, 2002, p. 200). Thus as a realizer of the interpersonal function of language, modality may be used as a linguistic tool to direct and control the behavior of the people. In line with this definition, and considering the texts as pieces of discourse "representing values embedded in ideology, attitudes or power relation outside of the text" (Sulkunen,& Torronen, 1997, p.45), within discourse analysis, modality concerns the writer's (or speaker's) attitude toward and/or confidence in the proposition being presented.
Modality, in its simplest sense, indicates a speaker's or writer's special way of conceptualizing a world view or ideology. According to Fowler "language does not allow us to say something without conveying an attitude to that something" (Fowler, 1997, p. 76). In other words hardly one can find a piece of written or spoken text as purely objective, neutral, or value-free. It is basically the writer's point of view, "angle of vision", "angle of telling", or authorial interest that determines the essence of a story's style and that provides the story with its particular "feel" and "color" (Simpson, 1993, p. 5).
2. Review of literature
Due to the importance of modality, some studies have focused on it trying to shed light on its function and frequency in written discourse. F. R. Palmer did fundamental work in the study of mood and modality in a typological way (Palmer, 2007). He emphasized the lexical forms of modality and various modal expressions across languages. He pointed out that modality can be classified into two groups, namely, propositional modality and event modality. Furthermore, he combined the classic dichotomy of epistemic and deontic modalities arguing that propositional modality includes epistemic and evidential modality while event modality covers deontic and dynamic modal types.
According to Palmer (2007. pp: 8-10), epistemic modality shows the speaker's "judgments about the factual status of the proposition", while evidential modality reflects "the evidence" the speaker has for its "factual status". When we are concerned about the possibility and necessity of an issue, we tend to use epistemic modality, which is also regarded as "inference" in a cognitive sense. On the other hand, deontic modality relates to "obligation or permission", a force from the external world, whereas …