Stagnation and the Natural Rate of Interest: Tracing the Roots of Lawrence Summers’s Theory of Secular Stagnation

Over the past decade, Lawrence Summers has argued that stagnation cannot be rectified by monetary policy because it is the result of a negative natural rate of interest. This analysis brings together two separate streams of thought: traditions in which stagnation has been connected to excessive saving linked to income distribution, or to diminishing investment demand; and a tradition centred on the natural rate of interest and its relationship to the market rate. However, they remained largely separated until Summers brought them together. Modern discussions of the natural rate stem from Knut Wicksell’s Interest and Prices (1898). However, although he came close to arguing that the natural rate might be negative during cyclical depressions, it was mainly under-consumptionists who argued for the possibility of stagnation. These two strands of thinking came closer in the interwar period but they remained separate. The main advocate of secular stagnation, Alvin Hansen, drew on the American Institutionalist tradition, not Wicksell. Postwar Keynesians did not pursue the idea of a negative natural rate even though Samuelson had provided a theoretical explanation. It was not until Summers that a negative natural rate, income distribution and the possibility of secular stagnation were brought together.