1、经典名篇 85Keynes, Lucas, and Scientific ProgressALAN S. BLINDER*In one of those marvelous coincidences of intellectual history, Robert Lucas was born the year after the publication of Keynes General Theory. For the first thirty-five years of their mutual lives, the two apparently coexisted in harmony.
2、But their relationship has been tumultuous ever since. Lucas has frequently criticized Keynesian economics as poor science; and it is precisely in that spirit that want to address the debate today.We all know the old joke about the professor who uses the same exam questions year after year, but chan
3、ges the answers. That joke encapsulates all too well what has happened to macroeconomics these last fifteen years and seems to reflect poorly on economics as a science. Or does it? On second thought, the best answers to scientific questions do change as new observations are made, as new experiments
4、are run, and as better theories are developed. The issue is whether the answers to important questions in macroeconomics have changed for good scientific reasons of for other reasons.The joke provides the framework for my talk. I will pose eight exam questions; and for each one I will summarize the
5、answers given by Keynes, by Lucas and his followers, and by modern Keynesians. I pick only questions that are answered differently by Keynesians and Locations and that are central to contemporary macroeconomic debates. The focus is on whether the Keynesian or new classical answers have greater claim
6、 to being “scientific.” Each student must answer every question. Are Expectations Rational?Keynes, though no stranger to probability theory, was nonetheless unequivocal in his denial that expectations are what we now call rational: a large proportion of our positive activities depend on spontaneous
7、optimism rather than on a mathematical expectationOnly a little more than an expedition to the South Pole, is it based on an exact calculation of benefits to come. Thus if animal spirits are dimmed and the spontaneous optimism falters, leaving us to depend on nothing but a mathematical expectation,
8、enterprise will fade and die1936,pp.161-62That attitude left a big loose end in The General Theory. Business investment is supposedly driven by “the state of long-term expectations,” but expectations are not pinned down by the theory, leaving substantial room for gyrations in macroeconomic activity
9、driven by autonomous changes in animal spirits. That hardly constitutes a tight scientific theory; but Keynes was probably happy to leave the loose end loose. Modern “sunspot theorists” have tightened up the argument considerably, in ways that Keynes might have found congenial.Lucas, of course, chan
10、ges the answer to yes. Was this change motivated by empirical evidence that subjective expectations match the conditional expectations generated by models-or even that actual * Princeton University, Princeton, NJ 08544. I am grateful for stimulating discussions or correspondence with Ben Brake, Andr
11、ew Capelin, Mark Gentler, Stephen Goldfield, David Roomer, Andre Shellfire, Robert So low, and Lawrence Summers. A version of this paper with footnotes and complete references is available on request to the author.经典名篇86expectations are unbiased and efficient? No. Indeed, Edward Prescott has boldly
12、asserted that “surveys cannot be used to test the rational expectations hypothesis”（ 1977,p.3）. Rather, economists are supposed to convert to rational expectations（RE ）because of the unloveliness of the ad hoc expectation mechanisms that preceded it and because RE is more consistent with their （unve
13、rified）worldview that people always optimize at all margins. As Thomas Sergeant put it: “Research in rational expectationshas a momentum of its ownthatstems from the logical structure of rational expectations as a modeling strategy” （1982, p. 382）. The momentum, you will note, does not stem from emp
14、irics. I leave it to you to decide whether these criteria are more like those that led physicists to dump Newton in favor of Einstein, or those that led artists to abandon Monet to follow Picasso.Modern Keynesians are split on this question. To some, the theoretical appeal of RE and the general idea
15、 that expectations should respond to policy changes are sufficient reason to conclude that “rational expectations is the right initial hypothesis.” Others harbor doubts. I think the weight of the evidenceboth from directly observed expectations and from indirect statistical tests of rationality（usua
16、lly in conjunction with some other hypothesis） is overwhelmingly against the RE hypothesis. Furthermore, RE is not without theoretical difficulties. We all know that RE models often have multiple equilibrium. More fundamentally, RE is theoretically coherent only in the context of a single agreed-upo
17、n model. In an economy in which different people hold different views of the world, the very notion lacks clarity. For example, if Paul Voucher announces today that on New Years Day he will raise M1 by 20 percent, I imagine Lucas and I will make different revisions in our expectations for, say, real
18、 GNP in 1987. Whose expectations are “rational?” Heterogeneous beliefs pose serious theoretical problems for RE, As scientists, then, I think we should be hesitant to embrace RE. Is there Involuntary Unemployment?Keynes said, nay screamed, yes. Lucas not only says no, but questions whether the phras
19、e has meaning. In his words, “To explain why people allocate time to unemployment we need to known why they prefer it to all other activities”（1986, p. 38）. Notice the words allocate and prefer. In his view, the unemployed are engaged in intelligent search or purposeful intertemporal substitution. H
20、e scoffs at the Keynesian tradition which, “by dogmatically insisting that unemployment be classified as involuntarysimply cut itself off from serious thinking about the actual options unemployed people are faced with”（1986, p. 47）.This is a tough question to adjudicate on scientific grounds since t
21、he issue is largely definitional and, as Lewis Carroll pointed out, everyone is entitled to his own definitions. In Lucass view, a person laid off from a job can, presumably, shine shoes in a railroad station or sell apples on a street corner. If he is not doing any of these things, he must be choos
22、ing not to do so. Both statements like this and reactions to them tend to be polemical. I guess dogmatism is in the ear of the beholder.However, a few pertinent facts should leaven the ideological debate. First, when the unemployment rate rises, it is layoffs, not quits, that are rising while consum
23、ption falls rather than risesall of which are bad news for search theory. Second, real wage movements are close to a random walkwhich is bad news for the intertemporal substitution approach. Third, unemployment is heavily concentrated among the long-term unemployed; in 1985, for example, people who
24、were jobless for 27 weeks or more constituted 54 percent of all unemployment and the expected duration of all unemployment and the expected duration of a complete spell of unemployment was 31 weeks. Can that be intertemporal substitution? Fourth, 经典名篇 87unemployed workers normally accept their first
25、 job offer, and those who are looking for work spend an average of only 4 hours per week on search activity. That hardly suggests a predominant role for search in explaining unemployment. Do Wage Movements Quickly Clear the Labor Market?Keynes certainly thought not, for such reasons as trade union a
26、ggressiveness, custom and inertia, and outright stubbornness. Lucas answers yesthough perhaps only in a broad sense. He has, for example, cited approvingly the competitive contract equilibrium approach in which workers have 100 percent unemployment insurance and, because of indivisibilities, are cho
27、sen randomly to work either, say, 40 hours a week or zeromeaning, of course, that unemployed workers have higher utility than employed ones. In Lucass opinion, there is “no reason to believe” that competitive models of labor markets that treat unemployment like leisure commit “a serious strategic er
28、ror.”No reason? I think the preponderance of the evidence says otherwise. Unemployment insurance replaces only about 40 percent of lost earning. Lately, only about one-third of the unemployed collect it, Where is the evidence that the unemployed are happier than the employed? Most economists think L
29、ucass distinguished predecessor at the University of Chicago had it right when he wrote, “Under any conceivable institutional arrangements, and certainly those that now prevail in the United States, there is only a limited amount of flexibility in prices and wages.” And it is hard, for me at least,
30、to look at what has gone on in this countrynot to mention in Europesince 1974 and see clearing labor markets. That the market clearing approach caught on in this environment is testimony to Lucass keen intellect and profound influence, not to economists respect for facts.More than just casual empiri
31、cism supports this view; numerous formal econometric studies reject the market-clearing hypothesis against some sort of disequilibria alternative. Unfortunately, it is usually spot-market clearing that is rejected. Equilibrium contracting models in which the wage plays little or no short-run a locat
32、ive role are difficult to formulate econometrically, much less to reject. Indeed, it is hard to know what observations could contradict such models; theory just leaves too many open possibilities.Nonetheless, certain observations are worth making. For one, several authors have pointed to interindust
33、ry wage differentials that are persistent across both time and spacedifferentials which are not easily squared with market clearing. Theoretically, we know that the wage rate may not be able to clear the labor market in a world of imperfect informationnot even in the long run. Of course, that effici
34、ency wage models can be built does not imply that they describe reality. But it does mean that market-clearing models have no particular claim to the theoretical high ground.In sum, the scientific basis for modeling labor marketsor goods markets for that matteras continuously clearing escapes me. Is
35、 the Natural Rate of Unemployment a StrongAttractor for the Actual Rate of Unemployment?Keynes thought not. Indeed, in his revolutionary zeal, Keynes spoke loosely （loose talk was a problem for Keynes）of an “unemployment equilibrium”which would seem to deny the natural rate any attractive force at a
36、ll. Lucas answers in the affirmative.Modern Keynesians have long had trouble with the masters notion that the masters notion that the 经典名篇88economy could equilibrate below full employment; they prefer to think of unemployment as a long-lasting disequilibria. In the United States at least, the validi
37、ty of the natural rate hypothesis has not been at issue for a long time. The argument, instead, is over whether the speed of convergence to the natural rate is rapid or glacial.On this, the American evidence is unequivocal and the European evidence is overwhelming. The U.S. civilian unemployment rat
38、e peaked at 8.9 percent in May 1975 and then took almost three years to get back down to 6 percent. It then peaked again at 10.7 percent in November-December 1982; now, four years later, it has yet to fall below 6.7 percent for even a single month. Some will argue that 7 percent is now the natural r
39、ate, without worrying much about how it grew so high. My view is that a theory that allows the natural rate to trundle along after the actual rate is not a natural rate theory at all.In Europe, the evidence is far more compelling. Unemployment rates rose more or less steadily from 1974 to 1985from 3
40、 to over 13 percent in Britain, from 2.8 to 10.5 percent in France, and from 1.6 to 8 percent in Germany. Some young men in these countries have never held a job and many never be productive workers. Facts like these have prompted several authors to seek models which explicitly reject the natural ra
41、te hypothesis in favor of hysteretic. And recent econometric work suggests hysteretic in postwar U.S. real GNP as well. It may well be that Keynesians caved in too readily to the natural rate hypothesis. Is there a Reliable Short-Run Philips Curve?Keynes, of course, did not answer this question; the
42、 Phillips curve came later. I include it on the exam because Lucas and Sergeant made it central to their attack on Keynesian economics. The alleged failure of the Phillips curve was their main piece of evidence that empirical Keynesian models “were wildly incorrect, and that the doctrine on which th
43、ey were based is fundamentally flawed.”（Please notice the adverbs.）This charge was repeated so often and with such certitude that it became part of the conventional wisdom. Unfortunately, it is, to coin a phrase, wildly incorrect. The fact is that, the Lucas critique notwithstanding, the Phillips cu
44、rve, wildly incorrect. The fact is that, the Lucas critique notwithstanding, the Phillips curve, once modified to allow for supply shocks（any one of several variables will do）, has been one of the best-behaved empirical regularities in macroeconomicsmuch better behaved, in fact, than we had any righ
45、t to expect. A long list of studies supports this conclusion. Nonetheless, Lucas continues to speak of the Phillips curve as an econometric basket case.Let me anticipate the obvious objection that saving the Phillips curve after the fact by adding a supply variable does not absolve it of its ex ante
46、 forecasting errors. It is true that, while Robert Gordons latest Phillips curves fit the data well, his pre-1972 equations do less well. And they did not predict the rise and fall of OPEC. But there is no sense in which new classical models either anticipated the error or pointed to the solution; l
47、ike Keynesian models, they were designed to analyze demand shocks. Events in the 1970s and 1980s demonstrated to Keynesian and new Classical economists alike that Marshalls celebrated scissors also comes in a giant economy size. It is a debaters tactic, and a poor one at that, to claim that supply s
48、hocks are outside the purview of Keynesian economics. Does a Change in the Money Supply have Real Effects?Keynes and the Keynesians answered yes, without bothering to distinguish between anticipated and unanticipated changes. Lucas and the Locations answer that money has real effects only if it is m
49、isperceived. In their view, a properly perceived injection of money is like a currency reform.经典名篇 89Here, again, the weight of the econometric evidence（though certainly not all of it）suggests that Keynes had the right answer after all. Robert Barrios alleged empirical demonstration that only unanticipated money has real effects did not hold up. Perceived changes in money are not neutral. Does Social Welfare Rise when Business Cycles are Limited?Keynes tacitly, but unequivocally, answered yes. If asked for proof, he probably woul
