  These claims about norms raise two difficulties. First, there is a potential regress of rules, that is, that explicit rules requires further rules to apply them, and so on. Second, this approach cannot capture how norms are often only implicit in practices rather than explicitly expressed (Brandom 1994, 18–30). Here Habermas sides with Pettit in seeing the central function of explicit norms as creating a commons that can serve as the basis for institutionalizing norms, a space in which the content of norms and concepts can be put up for rational reflection and revision (Pettit 1992, Habermas 1990).  Making such implicit norms explicit is thus also the main task of the interpretive social scientist and is a potential source of social criticism; it is then the task of the participant-critic in the democratic public sphere to change them. There is one more possible role for the philosophically informed social critic. As we have seen in the case of ideological speech, the reconstructive sciences “also explain deviant cases and through this indirect authority acquire a critical function as well” (Habermas, 1990, 32).