Previous research has shown the differential effects of task-related prompts on syntactic complexity, grammatical accuracy, and lexical diversity when L2 learners use writing prompts to produce a piece of writing. However, the extent to which the freedom in the selection of prompts affects these linguistic facets in L2 argumentative essays is still unknown. The present study, therefore, was designed to investigate differences between syntactic complexity, grammatical accuracy, and lexical diversity in argumentative essays. Seventy-one upper-intermediate male and female Iranian English-as-a-foreign language (EFL) learners from Imam Khomeini International University in Qazvin and Safir Plus institute in Tehran participated in this study. Five-paragraph essays were used to collect data, and SPSS (version 25) was used to analyze the data. Results of multivariate analysis of variance (MANOVA) showed statistically significant differences between syntactic complexity, grammatical accuracy, and lexical diversity. Results from post-hoc analyses revealed statistically significant differences between lexical diversity and grammatical accuracy as well as lexical diversity and syntactic complexity, but no statistically significant differences were found between grammatical accuracy and syntactic complexity in argumentative essays.
