<![CDATA[This research investigates how mood and modality systems are realized in teacher–student interactions during the teaching–learning process on WhatsApp, with the aim of explaining their contributions to discourse analysis and the implications for digital academic communication. Grounded in Systemic Functional Linguistics (SFL) as proposed by Halliday and Matthiessen (2014), this study examines how mood (declarative, interrogative, imperative) and modality (probability, obligation, permission, willingness) function as central elements of the interpersonal metafunction of language, enacting roles such as giving or demanding information and services. While previous studies have analyzed mood structures in classroom discourse and WhatsApp messages, few have examined modality alongside mood to explain how interpersonal meanings, politeness, and power relations are negotiated in teacher–student WhatsApp interactions. This integrated analysis therefore provides a more comprehensive understanding of interpersonal meaning in digital academic communication. Data were collected from five purposively selected authentic WhatsApp conversations involving academic communication between lecturers and students. The selected conversations represent common academic interactions, including requesting information, giving instructions, responding to messages, and providing clarification. Each clause was analyzed using the SFL framework to identify its mood type and modality. The findings reveal that declarative mood is most frequently used, especially by students, often to express politeness and cooperative responses. Interrogative moods, typically accompanied by modal expressions such as may, are used mainly by students for clarification and to show respect. Imperative moods appear exclusively in teachers' messages, reflecting their authoritative role in giving instructions. Modality of permission and willingness is prominent in student messages, whereas teachers tend to use modality of probability and obligation. These results demonstrate that even short, informal digital texts encode structured interpersonal meanings and reflect institutional roles through linguistic choices. The findings provide practical insights for teachers and students to develop clearer, more respectful, and more effective communication practices in digital academic environments. ]]>
