La place de la notion de chômage involontaire dans la théorie keynésienne de l'emploi

For a long time, the notion of involuntary unemployment occupied in the economic theory a central role. The expression appears very early, from the beginning of the 20th century, when the economists began to be interested in the unemployment. It indicates simply the unemployed who would agree to work at the prevailing wage rate. Keynes gave of this expression one much more narrow, different definition. The involuntary unemployment is, according to him, the unemployment which finds its origin in a deficiency in the demand for goods. At the beginning of 1970s, Phelps, Alchian and Holt set an analysis where the agents have only an imperfect information about wages and jobs. Their ideas were notably taken back and developed by Diamond, Mortensen and Pissarides. In the theory of the equilibrium unemployment, the opposition between voluntary unemployment and involuntary unemployment has no sense whatever we define the involuntary unemployment as Keynes or, more simply, as the excess supply of labour. But, more fundamentally, what this approach rejects is the idea that we can disregard the "frictional unemployment" in the analysis of the determination of the level of the employment. The decomposition of the unemployment in a series of categories - frictional, cyclic, voluntary, involuntary - may not help us in a theoretical or empirical analysis of the unemployment.