What syntactic patterns emerge in students' use of articles and modals? What are the reasons for these patterns? What implications do the findings of the study have for English language instruction in Botswana? Exactly 1556 essays comprising class assignments, written seminar presentations, test papers and examination scripts from 514 randomly selected students of the University of Botswana were analysed. The findings indicate that there were systematic omissions, substitutions and insertion of the definite and indefinite articles as well as recurrent use of the expression "can be able." Students' indication of different forms of epistemic modality was confined to the use of "could" while complex verb phrases involving negation had their constituents reordered such that the negative operator "not" consistently succeeded the perfective auxiliary. The study shows that the reasons for these errors are both intra- and interlingual, namely the complexities of the two grammatical structures, articles and modals, and the influence of L1. Since the Botswana Senior Secondary Assessment Syllabus specifies "accuracy" in the use of grammatical forms, by demanding high language achievement standards, this paper argues that a return to the teaching of basic grammar in the high school is important for the students' mastery of articles and modals.