Expectations and full employment : Hansen, Samuelson and Lange

International audienceFrom the outset, expectations were a central part of the first macrodynamic models and early growth theories. In the 1940s, a third line of research emerged which questioned the capacity of aneconomy to reach full-employment equilibrium. Starting with Alvin Hansen (1938) and culminating withOskar Lange (1944), the crux of the debate evolved from the existence of full employment equilibriumto analysis of its stability, suggesting an increased role for expectations and finally challenging theeconomic system’s global stability. The present paper traces those debates through the contributions ofHansen, Paul Samuelson and Lange. Using archives materials, we show that while Samuelson’s analysisof instability remained implicit, his correspondence reveals that he encouraged Oskar Lange to examineit more carefully. Lange’s results are presented in his 1944 Cowles Commission Monograph. We pointout that his contribution cannot be understood in isolation either from his exchanges with Samuelson orthe way that Keynesian ideas were being interpreted in the United States. The paper finally questionsSamuelson’s view on instability and expectations