The IMF uses crisis-defining economic ideas, and crisis legacy-defining ideas, to construct interpretations of economic crises in ways which prioritize particular policy or institutional responses, and rule out or marginalize others. The post-crash IMF enjoyed scope to shift the boundaries of ‘legitimate’ policy, involving heightened appreciation of ‘non-linear’ threats from losses of confidence, prolonged weak demand, and financial system fragilities and contagion. The policy corollaries of this Fund rethink were that economic stability has to be actively pursued through a wider range of policy and regulatory interventions by governments, central banks, the IMF, and other forms of authority and public power. In the context of the Great Recession, the Fund no longer considered it safe to assume an inherent tendency on the part of unfettered market forces in finance and the real economy to deliver the stability and full employment at the heart of its mandate.