The present study, as a data-based and diachronic one, has been done in order to investigate different types of pragmatic meanings belonging to the discourse marker “ya’ni” on thetical grammar level, and development of these meanings over time (centuries 4 to 14 A.H.). This study is based on Traugott and Dasher’s view (2002) on “subjectification spectrum” (non- subjective > subjective > intersubjective meanings). To collect research data, two literary books from each century were chosen. Then, all the occurrences of “ya’ni” in those books were manually identified. Finally, they were analyzed based on the paper’s analytical framework. The research data show that the discourse marker “ya’ni” acquires new pragmatic meanings such as textual, subjective and intersubjective ones on thetical grammar level, and moves away from its propositional meaning. It indicates that after pragmaticalization and transferring to thetical grammar, this discourse marker acquires new meanings through grammaticalization. The more it moves away from its propositional meaning, the more it is grammaticalized. There is also an order in forming these meanings so that textual meanings are formed at first; then subjective and intersubjective meanings appear in this discourse marker respectively. Introduction Discourse markers are linguistic units that have always been studied from various perspectives in different languages. Levinson (1983) studied discourse markers based on discoursal-pragmatic observations for the first time. He believes it is not possible to investigate these linguistic units within the framework of truth-conditional semantics. Osman (1995) suggests that we can make inferences about the speaker’s attitude through discourse markers. These linguistic elements can have different semantic roles based on the context in which they occur. Aijmer and Vandenbergen (2011) assert that analyzing discourse markers based on polysemy is in accord with grammaticalization theory. Accordingly, multifunctionality of discourse markers is the result of grammaticalization. The present study aims to investigate one of the Persian discourse markers (ya’ni) and its semantic development on the level of thetical grammar through the course of eleven centuries (4th to 14th) based on Heine’s pragmaticalization framework (2013) and Traugott & Dasher’s (2002) view on the “subjectification spectrum” (non-subjective > subjective > intersubjective meanings). Some studies on discourse markers have been done in Persian such as the ones conducted by Zoghdar Moghaddam (2002), Moghaddam Kiya (2004), Amouzadeh and Noora (2014), Noora (2015), Naghzguy Kohan and Meshkinfam (2019), and Abbasi et al. (2021). While most of these studies are synchronic including the one conducted by Amouzadeh and Noora (2014) on “ya’ni”, the present research examines “ya’ni” diachronically. Methodology and Theoretical Framework The present study is data-based, in which the development of the discourse marker “ya’ni” over eleven centuries (4th to 14th) was studied. To this end, two literary books, representative of each century, were chosen, and all occurrences of “ya’ni” were manually identified and analyzed based on the paper’s analytical framework (Heine’s approach, 2013, and Traugott & Dasher, 2002). Heine believes that the process leading to the rise of discourse markers is pragmaticalization, at the heart of which is a process called cooptation. He considers pragmaticalization and grammaticalization as distinct processes and asserts that, through cooptation, a linguistic unit is transferred from sentence grammar to thetical grammar, acquires new semantic functions based on the complicated network of the situation of discourse, and can be grammaticalized on thetical grammar level. Traugott & Dasher (2002) believe that discourse markers acquire different meanings through grammaticalization. More specifically, they propose three types of meaning that discourse markers can have in relation to the components of the situation of discourse. Those meanings are textual, subjective, and intersubjective. They suggest a “subjectification spectrum” (non-subjective > subjective > intersubjective meanings) representing the order in which these meanings appear. Results and Discussion The results of data analysis indicate that “ya’ni” (with the propositional content “meaning that”) acquires textual, subjective, and intersubjective meanings in relation to the different components of the discourse situation, which include text organization, attitudes of the speaker, and speaker-hearer interaction, respectively. The results also demonstrate that “ya’ni” gains these pragmatic meanings in the same order as proposed by Traugott & Dasher (2002). During the first three centuries (4th, 5th, 6th), “ya’ni” was only used in textual meaning. In the 7th century, the first occurrence of this discourse marker in subjective-intersubjective function is observed, which, of course, presupposes the presence of subjective meaning in this century. Finally, the first independent intersubjective meaning was encountered in the 8th century. Regarding the different types of textual meaning, the data indicates that there exists a relationship between the extent to which each type of textual meaning is similar to the propositional meaning of “ya’ni” and the time of its occurrence. The more it is similar to the propositional meaning, the earlier it is formed. Conclusion Based on the data analysis, it is concluded that, as Heine (2013) observes, “ya’ni” moves from sentence grammar to thetical grammar through cooptation, as the cornerstone of any pragmaticalization process. It is on thetical grammar level that “ya’ni” undergoes increasing grammaticalization, moving away from its original propositional meaning. If we consider grammaticalization as a continuum, the discourse marker “ya’ni” is in the initial parts of this continuum during the 4th, 5th, and 6th centuries. As time passes and this discourse marker acquires new pragmatic meanings, it moves forward in the grammaticalization process; therefore, it undergoes grammaticalization increasingly. This confirms Heine’s (2013) approach toward pragmaticalization. It also affirms Traugott & Dasher’s “subjectification spectrum” (2002) because textual meanings are the first meanings that are formed in “ya’ni”, then subjective and intersubjective meanings appear respectively.