“凯 恩斯主义者”的谬误在于他们的理论前提：一切衰退，不论何时发生，都完全是“协调问题”的结果——错误预期导致需求不足。几十年前我就做过预期效应的模 型，知道预期会产生种种影响。我同意，过去企业似乎会低估处于下坡路的竞争对手的减产和降价举措。这种过度的乐观预示着，对商品和劳动力的需求会出现不 足。因此，那时的任何刺激手段都可能产生凯恩斯效应。但如今，这种乐观无疑已从经济体系中消失。要刺激消费者需求或者政府需求，势必会推动利率上升、资产 价格下降，其幅度可能足以导致减少的就业多于增加的就业。
新古典主义者的谬误在于他们的如下信条：总就业虽然会受到种种冲击的影响，但可以说始终都在朝着某一正常水平回归。按照这种观点，就业不会因任何特 定需求的变化而改变。如果听到消费者手头吃紧，他们会说，市场会以降低利率做出回应，直至投资弥补了这一缺口。如果听到企业投资显得疲软、而且无法从新一 轮房地产热潮中得到支撑，他们会说，实际汇率的下跌将会带动净出口增加，从而填补缺口。他们不懂得，在开放型经济中，利率不可能大幅度下跌；而汇率下降会 对产出供给产生收缩效应，这可能会破坏进出口需求效应引发的扩张。
这些谬论使分析师们产生了一种错觉：不管怎样，全面复苏就在前方——得益于政府支出或者自我纠正的市场力量。依我看来，家庭、银行和许多公司糟糕的 资产负债表，正预示着一轮长久的“结构性衰退”。就业将会复苏，或快或慢，只要投资需求能够带动就业增加。考虑到增税（以支撑政府的支出）的就业效应，政 府在基础设施方面的支出是否还能否带来帮助？这存在着高度的不确定性。
最深刻的谬论是一种新思想：银行不当的激励机制导致了房地产泡沫，这个泡沫在破裂时，从根基上动摇了经济。所有人都会赞同，增加放贷和扩大建设遇到 了一个尴尬的事实，即当生产加快时，成本就会上升。由于这个缘故，价格趋于上涨。但这一分析解释不了房价连续4年的急剧上涨，其涨幅超过了60%。要解释 房价之所以如此大幅上涨，我们必须认识到，预期发挥了一定的作用。投机者似乎预期房子会涨到天价，这推动房价开始上涨；之后，由于投机者认为房价将逼近当 初的预期，房价继续攀升。银行则认为作为抵押物的房子会越来越值钱，因此提供了越来越多的抵押贷款。从这个角度来看，投机引发了危机。不当的激励机制既不 是危机发生的充分条件，也不是其必要条件。泡沫的出现要比不当的奖金早得多。这场危机也可以发生在一个上世纪50年代式的金融业中。这场危机的教训（虽然 人们尚未领会）是，市场中不存在魔力：相对于某个著名并得到认可的模型而言，支撑资产价格的预期不可能是“理性的”，因为根本不存在这样的模型。
这两个阵营都不会赢。他们这场伪辩论最严重的错误是，他们的肤浅和机械性——新古典主义像钟表一样机械，而凯恩斯主义就像水力学——令政策制定者误 入歧途，没有去探讨有关美国和英国经济活力的根本性问题。由于耽于凯恩斯主义理论和新古典主义理论，经济学付出了可怕的代价。如今，这些毫无新意、完全站 不住脚的观点所发出的蛊惑之辞，正在误导着政策制定者。
本文作者是2006年诺贝尔经济学奖得主、哥伦比亚大学(Columbia University)资本主义和社会中心(Center on Capitalism and Society)主任，著有《结构性衰退》(Structural Slumps)一书（1994年出版）
A FRUITLESS CLASH OF ECONOMIC OPPOSITES
In the theory wars, which are as much wars over policy choices, two very bad kinds of theories are driving out good theories.
Keynesian economics, which had been nearly forgotten inside the macro field, has found new voices from outside. They take the position that fiscal “stimulus” of all kinds is effective against slumps of all causes. Their strategy is to defeat their only popular rivals, the neoclassicals, by deriding their view that the employment downturn involves a contraction of the labour supply.
Neoclassical equilibrium theory, which some macroeconomists had grown sceptical of, has also found new practitioners. They take the position that, aside from bad policy moves, recessions, even “great” ones, are caused by random market events and corrected by market adjustments. Demand stimulus is of no use, since there is no systematic shortage of demand.
These spokesmen show little knowledge of the several theoretical perspectives in macroeconomics over the past 100 years. The “Keynesians” seem not to have studied Keynes and the neoclassicals misread or do not read Hayek. No wonder fallacies abound.
The fallacy of the “Keynesians” is their premise that all slumps, all of the time, are entirely the result of “co-ordination problems” – mis-expectations causing a deficiency of demand. Having modelled the effects of expectations decades ago, I know they have consequences. I agree that companies appeared to underestimate the cutbacks and price cuts of competitors on the way down. That excessive optimism signalled deficient demand for goods and labour. So any stimulus then may have had a Keynesian effect. By now, though, such optimism has surely been wrung out of the system. To pump up consumer or government demand would force interest rates up and asset prices down, possibly by enough to destroy more jobs than are created.
The fallacy of the neoclassicals is their tenet that total employment, though hit by shocks, can be said always to be heading back to some normal level. In this view, employment is impervious to shifts in any particular demand. If told that consumers are broke, they say that markets will respond by lowering interest rates until investment has filled the gap. If told that business investment looks weak and will not be getting the help of another housing boom, they say that a real exchange rate depreciation will fill the gap with an increase of net exports. They do not understand that interest rates cannot fall much in an open economy and that a weaker currency has contractionary effects on output supply that could spoil the expansion coming from the effects on export and import demands.
These fallacies lull analysts into the false sense that, one way or another, a full recovery lies ahead – thanks to government spending or to self-correcting market forces. As I see it, the poor state of balance sheets in households, banks and many companies augurs a “structural slump” of long duration. Employment will recover, quickly or slowly, only as far as investment demand will carry it. It is highly uncertain whether government spending on infrastructure would help, after taking into account the employment effects of the higher tax rates to pay for it.
The most profound fallacy is the newfangled idea that misalignment of incentives in banks caused the housing bubble – a bubble that, when it burst, shook the economy to its foundations. All can agree that increased lending and building ran into the awkward fact that costs increase when production is stepped up. On that account, prices sought a higher level. But that analysis does not capture the steep four-year climb in housing prices, which rose by more than 60 per cent. To account for so large an increase, we have to recognise that expectations played a role. Speculators appear to have expected that housing prices would go sky-high, so prices took off and then went on climbing in anticipation that those high prices were getting closer. The banks, seeing the houses offered as collateral were worth more and more, responded by supplying an increasing flow of mortgage loans. From this viewpoint, speculation drove the crisis. Misaligned incentives were not sufficient to do it – and not necessary either. Bubbles long predate bonuses. The crisis could have happened with a 1950s financial sector. The lesson the crisis teaches, though it is not yet grasped, is that there is no magic in the market: the expectations underlying asset prices cannot be “rational” relative to some known and agreed model since there is no such model.
The gravest error of the phony debate between two non-starters is that their superficial and mechanical character – the clockwork of the neoclassical system and the hydraulics of the Keynesian one – operate to distract policymakers from asking basic questions about the dynamism of the US and UK economies. Economics has paid a terrible price for its dalliances with the Keynesian and neoclassical theories. Now policymakers are being misled by the siren call of these same, hopelessly inadequate views.
The writer, winner of the 2006 Nobel prize in economics, is director of the Center on Capitalism and Society at Columbia University and author of Structural Slumps (1994)