This study investigated the strategic use of passive expressions by science and engineering university students in argumentative writing. To this end, 80 argumentative essays were analyzed to explore how the passive voice serves as a key indicator of students’ argumentative thinking patterns and writing development. Quantitative corpus analysis and qualitative examination reveal that students strategically employ passive expressions to objectively present evidence and counterarguments while deliberately avoiding the passive voice when emphasizing their core arguments or strengthening subjective claims. These findings suggest that passive expressions are valuable linguistic indicators of students’ argumentative thinking development. For writing instructors, particularly those teaching science and engineering students, understanding these patterns offers a concrete approach to observing and assessing students’ writing development. Instead of regarding the passive voice merely as a grammatical concept, instructors can use it as a pedagogical tool to monitor the manner by which students develop their argumentative thinking and writing skills. This approach offers a more visible and systematic means of elucidating the relationship between language choices and disciplinary thinking patterns in academic writing.