Description: The growing literature on conceptions of teaching held by university professors lacks a theorical framework. This investigation provide one resting on cultural historical psychology. It highlights generally unproblematized questions about relationship between conceptions of teaching, speech and cultural systems of meaning. In the present study, we argue that conceptions of teaching are tools and products of mediated action (Wertsch, 1998). By doing so, our attention is focused on the use of linguistic signs (Vygotski, 1962) when professors are making sense about teaching. Therefore, the material forms of utterances are studied. Our aim is to investigate these forms from a theorical and an empirical point of view. More exactly, this investigation is guided by the three following questions : (1) which psychological functions exert linguistic signs in the work of making sense ? How can we link these functions with empirical clues at the level of semiotic materiality of utterances ? Which hypothesis could we formulate about the relationship between university professors' work of making sense and the disciplinary culture they belong to ? Methodology: An instrumental case study was conducted with one physic's professor of university of Ottawa. We met him four times through different situations of interview. The goal was to stimulate reflection about teaching activity and personal experiences of teaching. The case study was characteristic of the dialogue between speculative and empirical moments of the investigation's process. Progressively, we distinguished two psychological functions exerted by linguistic signs in the work of making sense: reasonning and identity positionning. The analysis of these functions were grounded on material semiotic clues attesting qualitative variations in the composition and the style of language of utterances (Bakhtin, 1986). Conclusions: Data analysis showed three discursive forms of reasoning attested by empirical forms of composition : explanation, argumentation and narration. We observed two forms of identity positionning attested by empirical forms of style of language : alignment or non alignment on ideological position of a collective. We also formulated an hypothesis about forms of hybrids heteroglossia mixing language of folk pedagogy and language of academic discipline. They respected a kind of division of labor : the langage of folk pedagogy is used for making sense about students' learning process and how to act as a teacher on this process, and the language of the discipline is used for making sense about purposes of teaching and appropriate teaching methods.