I am much indebted to Antony Duff and Rowan Cruft for extensive comments on earlier drafts of this article. The article was presented at the 2007 ALSP Conference in Keele, at the 2007 NPTA conference in Glasgow and at a meeting of the Stirling Political Philosophy Group. I am grateful for all the suggestions received on these occasions, with particular thanks to Andrea Baumeister, Thom Brooks, Lynn Dobson, John Horton, Dudley Knowles and Sandra Marshall. Finally, I would like to thank Krystelle Bamford, Richard Dagger, Ezio di Nucci, Cécile Fabre, Mario Ricciardi, Bas van der Vossen, Kit Wellman and two anonymous referees of this journal for valuable comments on the final draft of the paper.