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假如凯恩斯还活着  

2009-06-14 07:58:20|  分类: 众说纷纭 |  标签: |举报 |字号 订阅

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作者:英国华威大学荣誉教授罗伯特?斯基德尔斯基(Robert Skidelsky)

2009-06-12

 

历史上充斥着著名的学术论战。在自然科学领域,结果通常是一方取得决定性胜利,优秀的科学取代愚昧的科学。如今,没有几个天文学家信奉托勒密的地心说,也不会有人相信燃素说。但在社会科学领域,情况就不同了:著名的论战比比皆是,但不存在决定性的胜利。实际上,这是社会科学的特征之一:这一领域的论战往往旷日持久,暂时失败的一方会重新集结力量,发起新的攻势。

经济学不是一门自然科学,一个明显的例证是,经济学史上不时发生毫无结果的论战。一百年前,古典理论占据统治地位。它“证明”,自由市场会自动自我调整到充分就业状态。市场会持续地处于充分就业状态,即使一时受到外部冲击而发生偏离,也会迅速恢复到充分就业状态。唯一能够破坏市场“无形之手”运转的,只有政府干预这只“有形之手”。

后来,随着1929-32年“大萧条”(Great Depression)的到来,约翰?梅纳德?凯恩斯(John Maynard Keynes)登上了历史舞台。凯恩斯“证明”,市场不具备自动实现充分就业的倾向。“无形之手”的失败,为政府实施旨在维持充分就业的政策提供了理论依据。

在大约30年的时间里,凯恩斯主义在经济学及经济政策中占据着主导地位。哈佛称王,芝加哥毫无地位。但芝加哥只不过是在卧薪尝胆。上世纪60年代,它发起了反攻。担任统帅的是米尔顿?弗里德曼(Milton Friedman),一批聪明杰出的年轻门徒追随着他。他们所要做的,是恢复古典理论的地位。他们“证明”,市场会瞬间(或近乎瞬间)地自我调整到充分就业状态。由于采用数学形式来表述,他们的证明更加令人印象深刻。适应性预期、理性预期、实际商业周期理论、有效金融市场理论,它们全都出自芝加哥学派,提出这些理论的人则摘取了诺贝尔奖。

政策制定者并不懂数学,但他们抓住了要领:市场是好的,政府是不好的。凯恩斯主义者败退了。在罗纳德?里根(Ronald Reagan)和玛格丽特?撒切尔(Margaret Thatcher)之后,凯恩斯主义者的充分就业政策遭到摒弃,市场监管逐步放宽。随后到来的,就是当前这场可与“大萧条”相提并论的经济危机,学术论战也再次打响。

博客圈的常客们肯定知道,当前这场论战主要围绕“刺激措施”的效果展开。英国《金融时报》的读者们,会隐隐在尼尔?弗格森(Niall Ferguson) 5月30日撰写的专栏文章——《给执着于凯恩斯的经济学家上历史课》——里闻到一丝硝烟味*。早在4月30日于纽约举行的一次公开研讨会上,弗格森就与经济学家、《纽约时报》专栏作家保罗?克鲁格曼(Paul Krugman)展开了争论。历史学家弗格森断言,巨额财政赤字会推高长期利率。这意味着,巨额赤字不会带来任何刺激效果:公共支出只会“挤出”私人支出。被激怒的克鲁格曼在博客上回应道,凯恩斯早已证明,这种挤出效应只有在充分就业状态下才会发生:如果存在闲置资源,财政赤字就不会在不推动经济增长的情况下推高利率。弗格森教授的无知言论只能证明,“我们生活在宏观经济学的‘黑暗时代',得来不易的知识已被彻底抛在脑后”。

然而,这不是一场经济学家和历史学家之间的战争,而是经济学专业领域内的战争——交战双方是新古典经济学家与新凯恩斯主义者。有意思的是,它几乎就是1929-30年凯恩斯与英国财政部那场争论的重演。英国财政部当时的观点是,依靠发债融资的公共支出,势必挤出等量的私人支出。凯恩斯回应道,如果是这样的话,任何加大私人支出的举措也会具有同样的效果。“简而言之,认为绝对无法增加就业的宿命论观点是毫无依据的。”

后来,英国财政部退而采取了一种更具防守性的立场。它辩称,增加政府支出的危险,不在于“实际”挤出资源,而在于“从心理上”挤出。如果人们对政府的偿付能力产生怀疑——克鲁格曼承认存在这种隐忧——就可能导致资本外逃,从而推高政府的举债成本。

我们一定要将同样的论据反复列举吗?在这场特定的争论中,我站在克鲁格曼一边,但我不认为弗格森的立场是倒退到了经济学的燃素说。这等于是将经济学当作自然科学看待。凯恩斯从不这样认为,他认为随着时间的推移,经济学探讨的对象总是在不断变化。

凯恩斯的观点是,在不同时期,我们需要不同的经济学模型。他的《就业、利息和货币通论》(The General Theory of Employment, Interest and Money)之所以精妙,就是因为包罗了种种适用于不同条件的模型。市场可能是以古典和新古典理论所描述的方式运转的,但并非必须如此。因此,重要的是采取措施预防不良行为。最后要说的是,凯恩斯革命并不是优秀的科学战胜了愚昧的科学,而是良好的判断战胜了糟糕的判断。

 

本文作者斯基德尔斯基勋爵的新书《凯恩斯:大师归来》(John Maynard Keynes: The Return of the Master)将于9月份由Allen Lane出版

* 见FT中文网《给克鲁格曼上历史课》一文

译者/岱嵩

 

 

Economists clash on shifting sands By Robert Skidelsky

2009-06-12

History is replete with famous intellectual battles. In the natural sciences, these have usually led to decisive victories, with good science ousting bad. There are few Ptolemaic astronomers left, or believers in the phlogiston theory of combustion. In the social sciences, the situation is different. There have been famous battles galore, but no decisive victories. Indeed, it is characteristic of the social sciences that their battles are interminable, temporary defeats being followed by the regrouping of the defeated forces for a renewed assault.

That economics is not a natural science is clear from the inconclusive engagements that have punctuated its own history. A hundred years ago the classical theory reigned supreme. This “proved” that free markets were automatically self-adjusting to full employment. They were either continually at full employment or, if disturbed by an outside shock, rapidly returned to it. The only thing capable of wrecking the workings of the market's invisible hand was the visible hand of government interference.

Then along came the Great Depression of 1929-32 and John Maynard Keynes. Keynes “proved” that markets had no automatic tendency to full employment. This failing of the invisible hand justified government policies to maintain full employment.

For 30 years or so Keynesianism ruled the roost of economics – and economic policy. Harvard was queen, Chicago was nowhere. But Chicago was merely licking its wounds. In the 1960s it counter-attacked. The new assault was led by Milton Friedman and followed up by a galaxy of clever young disciples. What they did was to reinstate classical theory. Their “proofs” that markets are instantaneously, or nearly instantaneously, self-adjusting to full employment were all the more impressive because now expressed in mathematics. Adaptive Expectations, Rational Expectations, Real Business Cycle Theory, Efficient Financial Market Theory – they all poured off the Chicago assembly line, their inventors awarded Nobel Prizes.

No policymaker understood the maths, but they got the message: markets were good, governments bad. The Keynesians were in retreat. Following Ronald Reagan and Margaret Thatcher, Keynesian full employment policies were abandoned and markets deregulated. Then along came the almost Great Depression of today and the battle is once more joined.

Haunters of the blogosphere will know that the main ground of the current engagement is about the effect of the “stimulus”. FT readers will have caught a faint whiff of the intensity of this battle in Niall Ferguson's column of May 30, headed “A history lesson for economists in thrall to Keynes”. Prof Ferguson and Paul Krugman, the economist and New York Times columnist, had previously locked horns at a public symposium in New York on April 30. The historian had asserted that large fiscal deficits would push up long-term interest rates. This implied they would have a zero stimulatory effect: public spending would simply “crowd out” private spending. An enraged Mr Krugman responded on his blog that Keynes had proved that such crowding-out could occur only at full employment: if there were unemployed resources, fiscal deficits would not drive up interest rates without also expanding the economy. Prof Ferguson's ignorant remarks only confirmed that “we're living in a Dark Age of macro- economics, in which hard-won know-ledge has simply been forgotten”.

However, this is not a debate between economists and historians. It is a battle within the economic profession – between the New Class-ical Economists and the New Keynesians. What is fascinating is that it is an almost exact rerun of the debate between Keynes and the British Treasury in 1929-30. The Treasury view was that bond-financed public spending was bound to diminish private spending by an equal amount. Keynes replied that if this were true it would apply to any new act of private spending. “In short, the fatalistic belief that there can never be more employment than there is is altogether baseless”.

Later the Treasury retreated to a more defensible position. The danger of extra government spending, it came to argue, lay not in the “physical” crowding out of resources but “psychological” crowding out. If doubts arose about the government's solvency – a concern Prof Krugman has acknowledged – it might lead to capital flight, which would push up the cost of government borrowing.

Are we doomed to rehearse the same arguments time and again? In this particular debate, I am on Prof Krugman's side, but I do not agree that Prof Ferguson's position represents a retreat to a phlogiston state of economics. This is to take economics to be like a natural science, which Keynes never believed it was, because he thought its subject matter was much too variable over time.

Keynes's view was that we need different economic models at different times. The beauty of his General Theory of Employment, Interest and Money was that it was general enough to accommodate a variety of models applicable to different conditions. Markets could behave in ways described by the classical and New Classical theories, but they need not. So it was important to take precautions against bad behaviour. Ultimately, the Keynesian revolution was a triumph not of good science over bad science, but of good judgment over bad judgment.

 

Lord Skidelsky's ‘John Maynard Keynes: The Return of the Master' will be published by Allen Lane in September

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