Abstract
In this theoretical paper we present an epistemic-logical model for analysis of students’ argumentation. The model is based on Vergnaud’s concepts- and theorems-in-action, on Duval’s distinction between epistemic and logical value of verbalised propositions, and on elements of Oostra’s intuitionistic existential graphs: a kind of graphical topological logic rooted in the Peircean thought, adapted to Mathematics Education research by considering also shifts to classical existential graphs. We use the model to discuss two examples taken from literature.