“Lucas and Sargent’s main argument was that Keynesian economics had ignored the full implications of the effect of expectations on behavior. The way to proceed, they argued, was to assume that people formed expectations as rationally as they could, based on the information they had. Thinking of people as having rational expectations had three major implications, all highly damaging to Keynesian macroeconomics. …
The first implication was that existing macroeconomic models could not be used to help design policy. … The second implication was that when rational expectations were introduced in Keynesian models, these models actually delivered very un-Keynesian conclusions. … The third implication was that if people and firms had rational expectations, it was wrong to think of policy as the control of a complicated but passive system. Rather, the right way was to think of policy as a game between policy makers and the economy. …
To summarize: When rational expectations were introduced, Keynesian models could not be used to determine policy; Keynesian models could not explain long-lasting deviations of output from the natural level of output; the theory of policy had to be redesigned, using the tools of game theory.”

—  Olivier Blanchard

Source: Macroeconomics (7th Edition, 2017), Ch. 24 : Epilogue: The Story of Macroeconomics

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Olivier Blanchard4
French economist 1948

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“One troublesome aspect is the place of rational expectations macroeconomics in the often political debate over Keynesian economics. At least implicitly, many people feel that what's bad for the rational expectations viewpoint is good for the Keynesian one, and vice versa. But it is hard to see how the problems in using the rational expectations approach to explain monetary nonneutrality can alleviate the theoretical and empirical shortcomings of the Keynesian model.”

Robert Barro (1944) American classical macroeconomist

Robert J. Barro, "Rational Expectations and Macroeconomics in 1984" (1984).

Olivier Blanchard photo

“Using the popular macroeconomic models of the time, Lucas and Sargent showed how replacing traditional assumptions about expectations formation by the assumption of rational expectations could fundamentally alter the results…. Most macroeconomists today use rational expectations as a working assumption in their models and analyses of policy. This is not because they believe that people always have rational expectations. Surely there are times when people, firms, or financial market participants lose sight of reality and become too optimistic or too pessimistic… But these are more the exception than the rule, and it is not clear that economists can say much about those times anyway. When thinking about the likely effects of a particular economic policy, the best assumption to make seems to be that financial markets, people, and firms will do the best they can to work out the implications of that policy. Designing a policy on the assumption that people will make systematic mistakes in responding to it is unwise.”

Olivier Blanchard (1948) French economist

Source: Macroeconomics (7th Edition, 2017), Ch. 16 : Expectations, Output, and Policy

“The original Lucas version of the new-classical macroeconomics combined the undeniable appeal of rational expectations with two more dubious assumptions inherited from Friedman (1968), that is, continuous market clearing and imperfect information, to form the foundation of the famous “Lucas supply function” (more justly, the Friedman-Lucas supply function). Soon Sargent and Wallace (1975) extracted from Lucas’s model its implication for monetary policy, the famous “policy-ineffectiveness proposition.” The demonstration by Barro (1977) that one could interpret historical U. S. data to be consistent with the proposition and the theory brought new-classical economics to its shortlived period of peak influence.”

Robert J. Gordon (1940) American economist

"Fresh Water, Salt Water, and other Macroeconomic Elixirs", 1989

“New-classical economics has been undeniably influential, but not in the way that its three prominent creators originally imagined. Its most important contribution to macroeconomics, the assumption of rational expectations, was stolen almost immediately, and applied more fruitfully, by the new Keynesians.”

Robert J. Gordon (1940) American economist

"Fresh Water, Salt Water, and other Macroeconomic Elixirs", 1989

Thomas J. Sargent photo

“These ideas have implications not only for theoretical and econometric practices but also for the ways in which policymakers and their advisers think about the choices confronting them. In particular, the rational expectations approach directs attention away from particular isolated actions and toward choices among feasible rules of the game, or repeated strategies for choosing policy variables. While Keynesian and monetarists macroeconomic models have been used to try to analyze what the effects of isolated actions would be, it is now clear that the answers they have given have necessarily been bad, if only because such questions are ill-posed.”

Thomas J. Sargent (1943) American economist

"Rational expectations and the dynamics of hyperinflation." 1973

Thomas J. Sargent photo

“My recollection is that Bob Lucas and Ed Prescott were initially very enthusiastic about rational expectations econometrics. After all, it simply involved imposing on ourselves the same high standards we had criticized the Keynesians for failing to live up to. But after about five years of doing likelihood ratio tests on rational expectations models, I recall Bob Lucas and Ed Prescott both telling me that those tests were rejecting too many good models.”

Thomas J. Sargent (1943) American economist

Thomas J. Sargent interviewed by George W. Evans & Seppo Honkapohja, Macroeconomic Dynamics, 9, 2005, 561–583.

Kenneth Arrow photo

“Not only is it possible to devise complete models of the economy on hypotheses other than rationality, but in fact virtually every practical theory of macroeconomics is partly so based. The price- and wage- rigidity elements of Keynesian theory are hard to fit into a rational framework, though some valiant efforts have been made. … But if the Keynesian model is a natural target of criticism by the upholders of universal rationality, it must be added that monetarism is no better. I know of no serious derivation of the demand for money from a rational optimization. … The use of rationality in these arguments is ritualistic, not essential.”

Kenneth Arrow (1921–2017) American economist

1970s-1980s, "Rationality of Self and Others in an Economic System", 1986

James Tobin photo

“Monetarism—both of the older Friedman version stressing adherence to money stock targets and of the newer rational expectations variety—has been badly discredited. The stage has been set for recovery in the popularity of Keynesian diagnoses and remedies. I do not mean to imply, of course, that there is some Keynesian truth, vintage 1936 or 1961, to which economists and policymakers will or should now return, ignoring the lessons of economic events and of developments in economics itself over these last turbulent fifteen years. I do mean that in the new intellectual synthesis which I hope and expect will emerge to replace the divisive controversies and chaotic debates on macroeconomic policies, Keynesian ideas will have a prominent place.”

James Tobin (1918–2002) American economist

James Tobin, "Keynes' Policies in Theory and Practice", Challenge (1983).
1970s and later

“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.”

Robert J. Gordon (1940) American economist

Robert J. Gordon, Are Procyclical Productivity Fluctuations a Figment of Measurement Error? (1992).

Richard A. Posner photo

“As conceived in this book, economics is the science of rational choice in a world─our world─in which resources are limited in relation to human wants. The task of economics, so defined, is to explore the implications of assuming that man is a rational maximizer of his ends in life, his satisfactions─what we shall call his “self-interest.” Rational maximization should not be confused with conscious calculation. Economics is not a thoery about consciousness. Behavior is rational when it conforms to the model of rational choice, whatever the state of mind of the chooser.(…) Nor is perfect rationality assumed; rational-choice thoery allows us to assume that rationality is “bounded” because of human cognitive limitations, although another way to think of those limitations is as costs of absorbing and using information.”

Richard A. Posner (1939) United States federal judge

Source: Economic Analysis of Law (7th ed., 2007), Ch. 1: The Nature of Economic Reasoning

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