VietTESOL International Convention 2026

Argumentative writing is a cornerstone of academic English instruction, yet it remains one of the most challenging genres for EFL learners to master-particularly when it comes to constructing logically sound arguments. This study examines the prevalence, types, and underlying causes of logical fallacies in the argumentative essays of English-major undergraduates at a teacher education university in Vietnam. Drawing on a mixed-methods design, the research analyzed 50 student essays to identify and categorize fallacies, distributed a questionnaire to 83 participants, and conducted semi-structured interviews with five volunteers. The findings reveal that logical fallacies are widespread in students' writing, with hasty generalization, false cause, and either-or reasoning among the most frequently occurring types. Qualitative and quantitative analysis further identifies several contributing factors, including inadequate pre-writing planning, overreliance on personal opinion rather than evidence, limited exposure to formal logic instruction, and time pressure during the writing process. These findings point to a gap between students' theoretical exposure to critical thinking and their ability to apply it in practice. Based on the results, the study puts forward a set of pedagogical recommendations, including the explicit teaching of logical reasoning, structured argument development activities, and peer feedback practices. More broadly, the research advocates for a repositioning of argumentative writing instruction as not merely a language task but a means of developing students' capacity to reason, evaluate evidence, and engage critically with ideas-competencies essential for both academic success and professional life in an increasingly complex world.