This research investigates the writing of EFL university students at the English department of a major university in Syria. Using Systemic Functional Linguistics as an analytical framework, the study applies Thematic analysis to students’ exam essays across two disciplines: language and literature, with the aim of exploring the differences in the language choices that students make in meeting the relevant disciplinary requirements. Another aspect of the study is to analyse student writing across different academic level with a view to identifying the nature of students’ developing writing maturity. Based on the assumption of an existing strong connection between the text and the broader context, the research investigates the possible influence of other contextual factors including the essay questions, model essays from the textbooks, and teacher’s views and perceptions. The findings from Thematic analysis point to the importance of interpersonal meaning in understanding this across-disciplinary variation in terms of building the argument and answering the essay question. The research shows potential pedagogical benefits in raising students’ awareness to the important function of different linguistic choices, particularly those with Thematic positions, in achieving the purpose of the text.