"The revolutionary impact of Keynesian Economics on contemporary thought stemmed in the main, we have argued, from Keynes' reversal of the conventional ranking of price and quantity velocities. In the Keynesian model price velocities are not infinite; it is sometimes said that the implications of the model result from the assumption that money wages are 'rigid.' This usage can be misleading. Income-constrained processes result not only when price-level velocity is zero, but whenever it is short of infinite." -- Axel Leijonhufvud, Keynesian Economics and the Economics of Keynes , p. 67 In other words, the classical theory of markets, as we still present it to students today, posits that when faced with a disequilibrium price, the market will make infinitely fast price adjustments, so that no quantity adjustments will ever occur. That, certainly, is a very special theory: in reality, price adjustments can never be infinitely rapid, so there will always be some ...