Most high school students are able to write arguments. However, most students are still unable to develop complex writing. The purpose of this research was to investigate the students' argumentative writing which displays various linguistic features and cognitive characteristics, and to investigate the conjunctions that fall into several categories (addition, opposition, causal, and time), which are markers of the complexity of the students' reasoning. The method used in this research was factorial analysis because it aimed to determine the students' linguistic and cognitive features in relation to improving the quality of the students' argumentative writing. The sample in this study was 350 high school students from grades 10 to 12. Analysis was carried out on the students' written argumentative essays which were written in the context of formal or academic language, transcribed and given an analysis code. The research findings show that students are able to demonstrate complex and high-level reasoning according to their use of conjunctions in their essays. The use of conjunctions based on class is relatively low in terms of the number of addition, contradiction, causal, and temporal conjunctions in each essay. The interclass correlation analysis shows that the essay length variable is in a stable condition, while student variability is higher in relation to the use of argument types and conjunctions. Based on the results following the testing of the predictability of conjunction use on argument sophistication, it was found that conflicting conjunctions contributed positively to argument sophistication apart from other variables (essay length, topic, gender, and student socioeconomic status). Contradictory conjunctions are the most complex conjunctions used by students using the integrative perspective. These conjunctions are also used to control the length and type of essay topic. Conjunctions can also contribute to the sophistication of the students' argumentative essays.