I outline a discourse-based account of presuppositions that relies on insights from the writings of Peter Strawson, as well as on insights from more recent work by Robert Stalnaker and Barbara Abbott. One of the key elements of my account is the idea that presuppositions are “assertorically inert”, in the sense that they are background propositions, rather than being part of the “at issue” or asserted content. Strawson is often assumed to have defended the view that the falsity of a presupposition leads to catastrophe, in the sense that a false presupposition “wrecks the assertive enterprise”. I argue that the discourse-based account in terms of assertoric inertia can explain how cases of presupposition failure can sometimes be non-catastrophic; there are cases in which the assertive enterprise operates smoothly, despite presupposition failure. The chief problem facing this line of argument is to account for cases in which presupposition failure is catastrophic. If presuppositions are assertorically inert, then how can their falsity ever wreck the assertive enterprise? I offer a principled account that delineates the circumstances in which false presuppositions are, and those in which they are not, catastrophic.