In this response to Mark Hayes's criticism of his article, 'Lucas on involuntary unemployment', the author insists on the need to draw a distinction between labour rationing (a market outcome) and unemployment (the activity of job seeking). Economic theory is mainly concerned with the former....

Keynes distinguishes three concepts: voluntary, frictional and (Keynesian) involuntary unemployment. Frictional unemployment is a Classical form of involuntary unemployment (not voluntary, as Lucas suggests), and reflects the Marshallian, rather than Walrasian, treatment of time and equilibrium....