Hume is widely believed to have held that constitutional stability depends entirely on institutional design predicated on the assumption that every person is a knave. His famous statement to this effect has been enormously influential, both historically and amongst contemporary scholars. It may come as a surprise, therefore, to learn that Hume did not think institutional design on the assumption of universal knavery was enough if seeking to establish long-term constitutional order. This was due to the ongoing threat posed by faction, and its capacity to subvert even the best-designed constitutions. The knave maxim was thus a necessary, yet not sufficient, condition for political stability. To see this, we must locate Hume's knave maxim in the wider context of his critique of parties, and especially his narrative construction in the History of England as centred around the difficulties of cultivating attitudes and dispositions of moderation amongst political actors, and his exploration of the limits of political science in ‘The Idea of a Perfect Commonwealth’.