Teacher monologue has received scant attention in English as a foreign language (EFL) classrooms which emphasise the teacher-and-student exchange. This study assumes that a key index of interaction would be the construction of knowledge, in which teacher monologue has a due role to play. The research is set in the context of EFL teaching at the tertiary level in China and examines teacher monologue with reference to the concept of making semantic waves in Legitimation Code Theory, which has been proved to be an important means of cumulative knowledge building in classroom practice. Systemic Functional Linguistics is used to analyse how semantic waves are generated on the ideational base of context dependency, i.e. the extent to which the reality construed in teacher monologue is dependent on its context. The transdisciplinary perspective attempts to provide one possible way to model linguistic choices in making semantic waves in EFL classrooms. The findings are the primary and secondary categories of semantic patterns representing a scale of context dependency. Semantic waves trace recurrent movements between relatively decontextualised and context-dependent meanings in the progression of semantic patterns. The shifts might scaffold students in the construction of knowledge essential for developing academic English proficiency.

Teacher talk plays an important role in second-language classroom interaction. Studies are informed by multiple theories and yet could be classified under two general approaches, i.e., cognitive and social. The two approaches provide different but complementary perspectives on the role of teacher talk in interaction, with a focus on either learners' cognitive change or their social participation. A conversation between them is called for in the academic field to understand their interdependent relationship as well as the loss and gain in the respective approach. However, the conversation is difficult to launch because the cognitive and social approaches have developed distinct perspectives on what constitutes language and how learning evolves, leading to seemingly incompatible descriptive paradigms. With reference to systemic functional linguistics (SFL), this article argues for reconciling the two approaches in the following aspects. First, the meaning-oriented view of language in SFL expands the learning scope beyond language forms and offers both approaches an angle to reconsider the focus of the interaction. Second, the semiotic view of learning in SFL blurs the boundary of cognition and language use and provides a perspective for understanding the mediated role of language in the cognitive and social processes of learning. Finally, the functions of scaffolding in teacher talk revealed by SFL based on a linguistic analysis may not only enrich the description of each approach but also enable findings across the two approaches to be comparable. It is anticipated that SFL would create new spaces for the conversation between the two approaches.