The dyadic rule–exception structure common to many legal systems has posed particular interpretive difficulties in international trade and investment law. Adjudicators have interpreted general and security exceptions in GATT, GATS and cognate provisions of investment treaties in divergent ways, and the analytic character of these provisions is under-theorised in the literature. This article argues that we should understand exceptions from a deontological perspective as permissions that affirm governmental regulatory capacity and thus limit the scope of the commands set out in the treaty. [---]