This study examines how instructional conversations revealed the ways two teachers' argumentative epistemologies (ideational and social process) shaped literacy events focused on the warranting of evidence. A microethnographic study of the literacy events within each teacher's respective instructional unit revealed that each teacher's epistemology shaped how students were asked to consider differing sources, relevancy, and sufficiency for warranting evidence within the context of writing extended argumentative essays. Events within an ideational epistemology required students to generate warrants as ideas to be applied to arguments in on-demand writing situations. Within a social process epistemology, students constructed warrants as a social practice appropriate for a specific rhetorical context. Each teacher supported his or her students in developing differing understandings of the nature of warranting. These findings highlight the importance of analyzing the teaching and learning of argumentative writing not only as written products of instruction but as a socialization into argumentative writing practices.