1. Introduction
In the past, modality was associated with the syntactic category of “mood,” and gradually, linguists such as Tavangar and Amouzadeh (2009), with reference to Lyons (1977), Palmer (1986), Bybee et al. (1944), Fillmore (1986), Givón (1995), Palmer (1998), and Narrog (2005), arrived at a distinction between semantic modality and grammatical modality. Research of this kind must be conducted in accordance with the nature of each language and its compatibility with the capacities and resources of that language. Since different approaches have each addressed a particular aspect of modality and there is no general agreement among them regarding the dimensions of modality, the authors seek to answer the question: What are the overall dimensions of modality? Despite intermittent descriptive and theoretical studies in the field of modality, scholars have still not reached an agreed-upon definition of this concept, and this in itself is evidence of the importance and complexity of modality. The aim of the present study is to introduce all dimensions of modality and provide a comprehensive representation of it.

2. Methodology
This research was conducted using a library-based method. In this manner, different views concerning modality were examined and, based on their differences and similarities, were placed into separate categories in the form of distinct perspectives. After comparing the proposed perspectives, the authors put forward another perspective that encompasses all of these viewpoints.

3. Discussion
There are four perspectives on modality, each of which approaches the subject from a different angle. Naghizadeh et al. (2011) regard modality primarily as semantic information related to the speaker’s insight or viewpoint concerning what is being said. Palmer’s (1990) perspective on modality is limited solely to grammatical modality, or, in other words, grammatical mood, because it is applicable only to verbs. The third perspective encompasses the views of grammarians and modern linguists, each of whom has described the concept of modality in a different way. Although each has adopted a different approach, they share one common point, namely that, in examining modality, they have focused only on the grammatical structure and surface structure of language. In the fourth perspective, Portner (2009) divides modal elements into three categories: sentential modality, subsentential modality, and discourse modality. Each of these perspectives offers a single version for all languages with regard to modality; however, the category of modality is entirely language-specific and is reflected across languages in various and diverse ways. It is therefore impossible to provide criteria that represent the category of modality uniformly across all languages. Research of this kind must be conducted in accordance with the nature of each language and its compatibility with the capacities and resources of that language. Accordingly, in the discussion of modality, emphasis should be placed on two important points: first, the examination of modality as language-specific; and second, the examination of modality at the discourse, sentential, and subsentential levels. This means that the rules of modality in one language cannot be imposed upon another language, because the structural configuration of modality differs from one language to another. Furthermore, in examining modality, all of its dimensions must be taken into consideration.

4. Conclusion
Drawing upon and synthesizing the various approaches to modality, the authors have presented the overall structure of the modality system in the form of a diagram. This diagram, which encompasses all dimensions of modality, including discourse modality, grammatical modality, and semantic modality, can serve as a credible model for examining modality in the Persian language. In the proposed diagram, the overall structure of modality is divided into three sections: the examination of contextual (discourse) modality; modality that is neither lexicalized nor grammaticalized. Subsentential modality; modality that is expressed only in sentence elements such as a lexicalized adjective. Sentential modality; modality that is grammaticalized in the verb.