According to the commonly accepted views about Keynes and Friedman, these two economists stand in sharp disagreement on almost everything, from the self-adjusting capacity of a decentralised market economy to the ability of the government to stabilise the economic system. It is true that their approaches are hardly reconcilable on some critical points, especially regarding the determinants of the money-demand function or more generally their respective understanding of the inter-relationships between the monetary side of the economy and its real side. But a careful reading of these two economists shows that they also shared deep matters of concern, especially regarding the kind of disequilibria at stake in a monetary economy. On the policy side, significant similarities ensue regarding the way they designed their respective policy devices.

Regarding the complementarities, our argument is that, compared to the rational expectations approach, Keynes and Friedman have in common to place the issue of expectations at the heart of their appraisal of a monetary economy functioning. They consequently also have in common to design the economic policy as a way to stabilise private agents' expectations. But this is not to erase strong divergences between Keynes and Friedman's respective approach. Our claim is that these two economists part company on the temporal perspective they respectively consider: Keyne' main concern is for long-term expectations whereas Friedman basically addresses the issue of the formation of expectations in the short period.

The paper is organised as follows. The first section deals with Keynes's approach to the formation of expectations in a monetary economy, the disequilibria that ensue and Keynes' conception of economic policy as a way to stabilise long-term expectations. The second section investigates Friedman's treatment of expectations, which can be viewed as symmetric to Keynes', the disequilibria that might occur in the short period and the role Friedman attributed to state authorities to dampen these disequilibria. The conclusion restates the ‘market failures versus government failures' in a historical perspective.