The study reported in this paper investigates how notions of the nature of mathematical knowledge and mathematical objects are constituted through the teaching practices of three university mathematics teachers at a Swedish university. The data consists of video recorded lectures, and the analyses were informed by classifications presented by Lerman and Davis and Hersh. The results indicate that different epistemological and ontological positions are indeed constituted through the discourse. Although the discourse is generally highly objectified, the ways in which mathematical objects are introduced differ. Mostly the discourse was within an absolutist paradigm, but there were also examples of how the socio-historical nature of mathematical knowledge is emphasized.