This study, in order to analyse the internal differentiation of pedagogic (scientific) knowledge, uses Habermas's development of Weber's work and, in particular, his socially constructed forms of instrumental-strategic, moral-practical and communicative rationalities. Additionally, it correlates these distinct forms of rationality to the "serial of languages" of pedagogic knowledge, which represents distinct conceptual systems such as the visible pedagogy, the child-centred liberal pedagogy (invisible pedagogy), and versions of critical pedagogy. The main point of this work is the indication of a second version of critical pedagogy, which is related to Habermas's form of communicative rationality. This sort of pedagogic knowledge thematises the social assumptions of the epistemological gap that exists between everyday and official school knowledge. (Contains 1 figure and 3 notes.)