The Dark Knowledge Problem: Why Public Justifications are Not Arguments

Abstract According to the Public Justification Principle, legitimate laws must be justifiable to all reasonable citizens. Proponents of this principle assume that its satisfaction requires speakers to offer justifications that are representable as arguments that feature premises which reasonable listeners would accept. I develop the concept of dark knowledge to show that this assumption is false. Laws are often justified on the basis of premises that many reasonable listeners know, even though they would reject these premises on the basis of the further considerations that speakers implicitly rely on for their support. Accommodating the fact of dark knowledge requires us to consider the civic virtue of speakers to be more important for public justification than the acceptability of their arguments to reasonable citizens. I sketch an alternative conception of public justification that incorporates these results and argue that it provides a rationale for ignoring the otherwise sound contributions of some participants in political deliberation.