Theme in the English mechanical engineering discourse: A systemic functional description

This article examines the use of theme in English mechanical engineering (ME) discourse from systemic functional linguistics (SFL) perspective developed by Halliday and other systemists.By analyzing a variety of texts including eight technical descriptions, seven research articles, and nine user manuals from the field, the study explores how topical, interpersonal and textual themes, simple and multiple themes, marked and unmarked themes, constant, linear themes and derived ones (or split rhemes) are employed to structure information, emphasize key concepts, enhance coherence and cohesion, and facilitate the communication of technical knowledge.The paper highlights the interplay between ideational, interpersonal, and textual metafunctions within ME discourse, revealing how thematic choices contribute to the clear communication of technical content.The findings show a dominance of topical, simple, unmarked and constant themes as well as demonstrate that theme selection in this kind of discourse not only serves organizational purposes but also reflects the communicative and functional needs of the technical discipline, ultimately facilitating the transmission of specialized knowledge to novices.Moreover, interpersonal, textual, multiple, linear and derived themes appear more frequently in academic and instructional texts than in descriptive ones.This research also provides insights into the linguistic strategies engineers use to structure discourse and offers a detailed functional description of thematic patterns in technical communication and presents implications for both practitioners and educators in the ME field.