The grammar of classroom authority: mood, modality, and interpersonal meaning in Indonesian upper-secondary classroom discourse

Introduction How teachers and students exchange meanings in the classroom shapes both what is learned and how learners position themselves as knowers. This study examines interpersonal meaning in Indonesian upper-secondary classroom discourse through systemic functional linguistics (SFL), asking how mood system, mood structure, and modality are realised by teachers and students, and what these realisations reveal about the tenor of classroom relations. Methods Six complete Indonesian-language (Bahasa Indonesia) lessons at three private senior high schools in Medan, Indonesia, were recorded, transcribed, and segmented into clauses, yielding 4,817 mood-classified major clauses alongside minor and elliptical clauses. Results Teachers produced 76.1% of all mood-classified clauses. Declaratives dominated both teacher talk (71.1%, including negatives) and student talk (92.4%). Teachers monopolised interrogatives (20.2% of their clauses) and imperatives (6.5%), while student imperatives and offers were nearly absent. Students produced elliptical clauses at more than twice the rate of teachers. Modality analysis revealed that teachers favoured high-value obligation (143 of 147 tokens) and median probability; student modality was rare and of low value. Discussion This profile is consistent with epistemic certainty and directive authority. Tenor analysis of vocatives, pronouns, and lesson openings confirmed an asymmetrical, transmission-oriented relationship, although traces of student contestation were observed. The findings provide a lexicogrammatical benchmark for assessing the dialogic ambitions of Indonesia's student-centred curriculum reforms and extend SFL classroom-discourse analysis to a non-European national language.