Jacques Derrida’s approach to lair in Force of Law: “The Mystical Foundation of Authority” has nothing short of paradigm status in the field of poststructuralist and deconstructionist legal sociology and critique. Given such an image of lair, the indeterminacy of legal concepts appears a disruptive factor within the legal order, undermining all efforts to establish order. Precisely because of this destabilizing effect, indeterminate phenomena, including legal constructions such as indeterminate legal concepts (unbestimmte Rechtsbegriffe), are granted a central status in poststructuralist critiques of power. In this article, through an examination of the indeterminate legal concept of public morality (gute Sitten), referred to in the blanket clause of § 138 of the German Civil Code, I argue to the contrary that, from a functional perspective, this technique of using indeterminate legal concepts stabilizes the legal order. Phis points to problems in the theoretical architecture of postructuralist and deconstructionist approaches. They are in danger of losing touch with the very object they claim to consider. Phis has consequences both for (legal) sociological theory and for the intended strategy of the critique, having an impact that goes well beyond the legal realm.