This article identifies a blind spot in constructivist theories of representation and their account of legitimacy in terms of the challenge posed by ecologies of social ignorance, generally and especially during foundational moments. Social ignorance is conceptualised here not merely as the absence of knowledge or true belief but as a social practice of legitimising epistemically problematic political imaginaries and the institutional systems they underpin. In dialogue with social epistemologists and phenomenologists, the article shows how representation can nurture social ignorance, despite the availability of ample opportunities for political contestation and alternative opinion formation. A permanent feature of democratic politics, this problem becomes most salient during moments of constitutional re-founding, such as regime change, post-conflict reconstruction or constitutional referenda, when representative claims can reconfigure a community’s political imaginary, rendering it more or less ignorant. The representative claims made by the Vote Leave’s key figures during the Brexit referendum campaign serve as illustration. © The Author(s) 2021.