‎ Investigating the thematic structure in Academic English Textbooks for Special Purposes :The Comparison of Iranian and non-Iranian Writings

In Functional Grammar, theme is a structure that plays a key role in message processing and it refers to the subject matter to which the message relates. Due to having such role, this linguistic concept is considered in the analysis of educational texts by those interested in this field. In the present study, drawing upon textual metafunction of Functional Theory, finding possible similarities and differences in the theme selection of universities’ ESP textbooks in Humanities and Engineering disciplines by Iranian(SAMT) and non-Iranian authors is of significant interest.The method of this research is descriptive-analytical and the statistical population is 32 readable texts from the sources.The results showed that there is no significant difference in the use of themes in the corpus, among authors,and between dicsiplines; so that,100% experimental themes, simple themes more than multiple themes (76% vs. 24%) and textual themes more than interpersonal themes (22.5% vs. 2%) have been used by all authors. It seems that the main reason for this similarity is related to the genre similarity of writings. Based on the findings, the following results can be inferred: Theme is meaningful in the English language and is taken into account in the writing of academic textbooks, especially in ESP; the remarkable similarity and the writing framework alignment of different authors with Halliday’s systemic functional theory suggests the usefulness of this view in the evaluation of  scientific books; the authors' attention to the effectiveness of the textual metafunction as an efficient resource in the construction, development, and coherence of texts, as well as its efficiency in academic textbooks division to different genres is elaborated; finally, in the light of these findings, it can be said that choosing a textbook based on the criteria that the author is Iranian or not, is not desirable.