Academic discourse has always been the focus of many linguists, especially those who have been involved with English for Academic Purposes (EAP) and discourse analysis. Persuasion, as part of rhetorical structure of academic writing, is partly achieved by employing modality markers. Adopting a descriptive design, the present study was carried out to compare the use of modality markers in terms of frequency and their categorical distribution in two academic books, written in English, in the field of Applied Linguistics by native English and non-native Iranian authors. Quirk, Greenbaum, Leech, and Svartvik’s (1985) model of modality was employed as an analytical framework to identify the type of modal verbs. The frequency of different types of modal verbs was calculated per 100000 words and the significance of difference in their distribution was checked through Chi-square nonparametric inferential statistics. The results of the statistical analyses did not show any significant difference in the overall distribution of modality (both epistemic and root) markers. However, significant differences were observed in the categorical distributions of modal verbs in two corpora. The results were attributed to the non-native writers’ lack of awareness of the conventional rules of English rhetoric, and the lack of explicit instruction in this field. The findings could offer pedagogical implications for those involved in syllabus design and materials development in general and English writing courses in particular.
