The foundations of knowledge, which include language and even economics, can be subject to intellectual earthquakes.1 Such earthquakes test the robustness of established views and may lead to previously unanticipated directions for thought. A classic example is the impact of the Great Depression on the direction of economics, as it led to the development of an obligation for the government to run countercyclical economic policies and subsequently to the growth of national income accounting, which laid the basis for the development of macroeconomic modelling. These earthquakes expose fissures between different schools of thought, and economics continues to be torn between those who are, broadly speaking, expansionists and those who are more conservative.2 Indeed, the spectre of the Great Depression with its images of long food queues and marchers asking for work has had a particular hold on central bank thought; so much so that at the time of the financial crisis and in its aftermath, both the Chairman of the Federal Reserve and the Governor of the Bank of the England were academic economists who had written on the events of the Great Depression.