During the relatively brief period in the late 1960s when economists were pondering the possible obsolescence of business cycles, the scholarly disci… - Robert J. Gordon

Part of the downfall came early and on theoretical grounds, with the realization that real-world information lags for aggregate variables like the price level and money supply were much too short to rationalize the persistent multiyear deviations from equilibrium that seemed to characterize business cycles in most industrialized countries. The second dubious assumption, continuous market clearing, was viewed more critically once it was recognized that it was not an inextricable concomitant of rational expectations, especially when Stanley Fischer (1977) and Edmund Phelps and John Taylor (1977) showed that rational expectations could be embedded in a model containing real-world institutional features like multiperiod wage and price contracts to generate nonmarket-clearing behavior. Once Fischer and Phelps-Taylor had shown that rational expectations by itself was a necessary but not a sufficient condition to validate new-classical policy conclusions, the race was on to develop the new-Keynesian theory based on rational expectations and one or another institutional impediment to continuous market clearing.

Since the late 1960s macroeconomic debates in the United States have centered on the competing interpretations of the new classical and new Keynesian macroeconomics. The initial new classical model developed in the early 1970s by Robert E. Lucas, Jr., combined market-clearing, imperfect information, and rational expectations. After much testing, it was eventually rejected in the late 1970s for failing to explain why business cycles lasted on average four years while information delays lasted only a few weeks. It was soon replaced by a second new classical approach, the Real Business Cycle (RBC) model, which was also based on continuous market clearing and competitive equilibrium, but now generated the business cycle through serially correlated procyclical technology shocks.

But business cycles as a subject for study have enjoyed a revival for at least a decade now, stimulated in part by the severity of the 1974-75 and 1981-82 recessions and in part by the intellectual ferment surrounding the development of the "equilibrium business cycle model" and the attention paid to the seminal work of Robert E. Lucas, Jr., contained in his book Studies in Business Cycle Theory (1981). Indeed, there is no longer any need to lament the passing of economics courses explicitly carrying the title "Business Cycles," since the topic of business cycle behavior and analysis has so infiltrated courses carrying the title "Macroeconomics" that the two subjects have become almost interchangeable. 2 In this light it is fitting that the major research program of the NBER in this area is called "Economic Fluctuations" rather than "Macroeconomics."