It is not a new insight that what is probably the early fifteenth century’s most sustained and thoughtful response to Piers Plowman, the alliterative, allegorical dream vision Mum and the Sothsegger, is also a sophisticated critique of political corruption in contemporary England. What has not yet been addressed among studies of the poem’s political allegory and use of personification, though, is the extent to which its critique hinges upon a specific medieval legal idea whose implications continue to haunt us even up to the present day: that one person may be held responsible for (and even punished for) another’s sin because he or she has consented to it by remaining silent. Crucially, the poem insists (as in my title) that this theory is common knowledge, the property of all. My current book project focuses on the history of this idea, and its deployment in allegorical poetry and rhetorical prose between the late twelfth and mid fifteenth centuries. In my paper at OSU I’ll show what this broader perspective can contribute to our reading of Mum and the Sothsegger.