Who drives domestic institutional change in the face of international economic crisis? For materialists, self-interested actors struggle for material gains during exogenously generated crises. For constructivists, norm entrepreneurs strategically construct how crises should be interpreted to justify certain institutional reforms. While both these approaches are analytically powerful, they suffer from an implicit view of legitimacy as established by elite command or proclamation during periods of uncertainty. This article adds an extra piece to the puzzle of which institutional reforms are selected in the construction of a crisis. It suggests that everyday discourses constructed by mass public agents, or non-elites, provide impulses for elite actors to select institutional reforms that will receive social legitimacy. The article re-examines the case of interwar Britain, arguing that a "legitimacy gap" between elite and mass understandings informed institutional experimentation during the 1920s and 1930s, fertilizing the eventual "Keynesian Revolution." In this way, this article seeks to show how the expressive practices and changing conventions of non-elite agents can shape institutional development. It also suggests that an "agent-centered constructivism" interested in explaining institutional change may be well served by taking into account popular as well as elite views.