Comment: Lucas on involuntary unemployment

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. Lucas contradicts both Keynes and Pigou in asserting that there are always immediate vacancies for unskilled labour, and abstracts from the very problem that Keynes seeks to address. If voluntary unemployment is re-defined appropriately, as De Vroey helpfully suggests elsewhere, the prefix ‘involuntary’ is dispensable, not because all unemployment is voluntary, as Lucas would have it, but because it is all involuntary.