宏觀經(jīng)濟(jì)理論為何需要重建？

Economics is, like medicine (and unlike, say, cosmology), a practical discipline. Its goal is to make the world a better place. This is particularly true of macroeconomics, which was invented by John Maynard Keynes in response to the Great Depression. The tests of this discipline are whether its adepts understand what might go wrong in the economy and how to put it right. When the financial crisis that hit in 2007 caught the profession almost completely unawares, it failed the first of these tests. It did better on the second. Nevertheless, it needs rebuilding.

經(jīng)濟(jì)學(xué)是一門實(shí)用學(xué)科,與醫(yī)學(xué)一樣，而與(比如說)宇宙學(xué)不一樣。經(jīng)濟(jì)學(xué)的目的是讓這個(gè)世界變得更美好。宏觀經(jīng)濟(jì)學(xué)尤其如此，它由約翰•梅納德•凱恩斯(John Maynard Keynes)在對(duì)大蕭條(Great Depression)做出回應(yīng)時(shí)所創(chuàng)。對(duì)這門學(xué)科的檢驗(yàn)在于，宏觀經(jīng)濟(jì)學(xué)專家是否了解經(jīng)濟(jì)中哪里可能出問題以及如何糾正。2007年爆發(fā)的金融危機(jī)幾乎讓該學(xué)科完全始料不及，第一次檢驗(yàn)不及格。第二次的成績(jī)好一些。但它需要重建。

In a blog for the Financial Times in 2009, Willem Buiter, now at Citi, argued that: “Most mainstream macroeconomic theoretical innovations since the 1970s . . . have turned out to be self-referential, inward-looking distractions at best.” An exceptionally thorough analysis, published in the Oxford Review of Economic Policy, under the title “Rebuilding Macroeconomic Theory”, leads this reader to much the same position. The canonical approach did indeed prove gravely defective. Moreover, top class professional economists differ profoundly on what to do about it. Socrates might say that awareness of one’s ignorance is far better than the illusion of knowledge. If so, macroeconomics is in good shape.

在2009年為英國(guó)《金融時(shí)報(bào)》撰寫的博客中，現(xiàn)供職于花旗(Citi)的威廉姆•比特(Willem Buiter)指出：“自上世紀(jì)70年代以來的多數(shù)主流宏觀經(jīng)濟(jì)理論創(chuàng)新……被證明充其量是自我參照、封閉的消遣。”發(fā)表在《牛津經(jīng)濟(jì)政策評(píng)論》(Oxford Review of Economic Policy)的一篇非常深入的分析文章題目為“重建宏觀經(jīng)濟(jì)理論”，它引導(dǎo)讀者得出大致相同的觀點(diǎn)。墨守成規(guī)的研究方法確實(shí)被證明存在嚴(yán)重缺陷。另外，頂尖職業(yè)經(jīng)濟(jì)學(xué)家對(duì)于如何解決這個(gè)問題存在深刻分歧。蘇格拉底(Socrates)可能會(huì)說，意識(shí)到自己的愚昧無(wú)知要比處于知識(shí)幻覺好得多。如果是這樣的話，宏觀經(jīng)濟(jì)學(xué)目前狀況良好。

As David Vines and Samuel Wills explain in their excellent overview, the core macroeconomic model rested on two critical assumptions: the efficient markets hypothesis and rational expectations. Neither looks convincing today. It is questionable whether it is even possible to have “rational expectations” of a profoundly uncertain future. Such uncertainty helps explain the existence of institutions — money, debt and banks — whose effects are so significant and yet were largely ignored in standard models. It is better to be roughly right than precisely wrong. Thus, Hyman Minsky’s view of the dangers of speculative tendencies in finance was roughly right, while many of the brightest macroeconomists proved precisely wrong.

正如大衛(wèi)•維內(nèi)斯(David Vines)和薩姆•威利斯(Sam Willis)在二人精彩的概述中解釋的那樣，核心宏觀經(jīng)濟(jì)模型取決于兩個(gè)重要假設(shè)：有效市場(chǎng)假說和理性預(yù)期。這兩點(diǎn)現(xiàn)在看上去都沒有說服力。對(duì)高度不確定的未來是否有可能有“理性預(yù)期”甚至都存在疑問。這種不確定性有助于解釋貨幣、債務(wù)和銀行等體系的存在，這些體系的影響非常重要，但在標(biāo)準(zhǔn)模型中基本被忽視。大致正確好于完全錯(cuò)誤。海曼•明斯基(Hyman Minsky)有關(guān)金融領(lǐng)域投機(jī)傾向危險(xiǎn)性的觀點(diǎn)大致正確，而很多最聰明的宏觀經(jīng)濟(jì)學(xué)家被證明是完全錯(cuò)誤的。

It is not good enough to argue that the canonical model works in normal times. We need also to understand the risks of crises and what to do about them. This is partly because crises are, as the Nobel-laureate Joseph Stiglitz notes, the most costly events. A macroeconomics that does not include the possibility of crises misses the essential, just as would a medicine that assumes away the possibility of heart attacks. Moreover, crises are endogenous: that is to say, they come from within the economy. They are a result of the interaction between tendencies towards excessive optimism and the fragility of any system of highly leveraged financial intermediaries.

辯稱標(biāo)準(zhǔn)模型在常規(guī)時(shí)期有用是不夠的。我們還需要了解危機(jī)的風(fēng)險(xiǎn)以及如何應(yīng)對(duì)。這在一定程度上是因?yàn)槲C(jī)是代價(jià)最高的事件，正如諾貝爾獎(jiǎng)得主約瑟夫•斯蒂格利茨(Joseph Stiglitz)指出的那樣。不包括危機(jī)可能性的宏觀經(jīng)濟(jì)學(xué)沒有抓住重點(diǎn)，就好像一種藥物不假設(shè)出現(xiàn)心臟病的可能性。另外，危機(jī)是有內(nèi)源性的：這就是說，它們來自經(jīng)濟(jì)內(nèi)部。它們是過分樂觀的傾向以及高杠桿金融中介體系的脆弱之間相互作用的結(jié)果。

My colleague Martin Sandbu notes, in particular, the possibility of “multiple equilibria” — the idea that economies might end up in self-reinforcing bad states of the world. This possibility makes it vital to respond to crises forcefully. Doctors’ first response to a heart attack is, after all, not to tell the patient to go on a diet. That happens only after they have dealt with the attack itself.

我的同事馬丁•桑德布(Martin Sandbu)特別指出“多重均衡”的可能性，這種觀點(diǎn)認(rèn)為，經(jīng)濟(jì)可能最終會(huì)讓全球的糟糕狀態(tài)自我強(qiáng)化。這種可能性讓對(duì)危機(jī)做出有力應(yīng)對(duì)變得至關(guān)重要。畢竟，醫(yī)生面對(duì)心臟病的第一反應(yīng)不是告訴患者要節(jié)食。這種事情只有在他們處理過心臟病后才會(huì)發(fā)生。

So a big question is not only whether we know how to respond to a crisis, but whether we did so. In his contribution, the Nobel laureate Paul Krugman argues, to my mind persuasively, that the basic Keynesian remedies — a strong fiscal and monetary response — remain right. Also vital is swift revitalisation of the banking system. The contrast between the swifter US recovery and the dreadful delays in the eurozone gives striking support for this view. Essentially, the latter lost five years before the recovery began.

因此，重要問題不僅是我們是否明白如何應(yīng)對(duì)一場(chǎng)危機(jī)，還有我們是否這么做了。諾貝爾獎(jiǎng)得主保羅•克魯格曼(Paul Krugman)指出(我認(rèn)為很有說服力)，凱恩斯的基本補(bǔ)救方法——強(qiáng)有力的財(cái)政和貨幣應(yīng)對(duì)措施——仍然正確。同樣重要的還有銀行體系快速恢復(fù)活力。美國(guó)經(jīng)濟(jì)更快復(fù)蘇與歐元區(qū)經(jīng)濟(jì)復(fù)蘇的可怕延遲之間的對(duì)比，為這種觀點(diǎn)提供了明顯支持?；旧?，歐元區(qū)失去了5年才開始復(fù)蘇。

A comparison between what happened in the 1930s and this post-crash period shows we have indeed learnt some important things. Compared with the Great Depression, the immediate declines in output and rises in unemployment were far smaller. Moreover, prices have also been far more stable this time. These are true successes. Nevertheless, after a decade, the level of output per head, relative to pre-crisis levels, is less impressive: Germany and the UK did even better last time. Moreover, the worst hit eurozone countries have suffered badly, by any standards. This recovery really has not been a triumph.

比較一下上世紀(jì)30年代和此次危機(jī)之后的時(shí)期，我們會(huì)發(fā)現(xiàn)，我們實(shí)際上學(xué)到了一些重要的東西。與“大蕭條”相比，產(chǎn)出的立即下滑以及失業(yè)率上升幅度要小得多。另外，這次物價(jià)也一直穩(wěn)定得多。這些是真正的成功。然而，在危機(jī)發(fā)生了10年后，相對(duì)于危機(jī)前的人均產(chǎn)出水平則不如人意：德國(guó)和英國(guó)甚至上一次表現(xiàn)得更好。另外，以任何標(biāo)準(zhǔn)來衡量，遭受最嚴(yán)重打擊的歐元區(qū)國(guó)家都受損嚴(yán)重。這次復(fù)蘇實(shí)際上算不上成功。

This suggests that fixing a huge crisis after the event is terribly hard. The obvious need then is to make economies more resilient. Even if we do not fully understand the economic dynamics, the broad lessons for the reform of our economies seem clear. Economies would be more resilient if they were less highly leveraged and, in particular, if they depended less on holdings of money backed by risky assets owned by the highly leveraged financial intermediaries known as banks. Obvious solutions include eliminating the incentives towards leverage in our tax systems, encouraging greater use by the economy of equity finance and debt that can be readily converted into equity, raising the reserve and capital requirements of banks and moving swiftly towards the issuance of digital central bank cash.

這表明，事后修復(fù)一場(chǎng)嚴(yán)重危機(jī)非常困難。因此，明顯有必要讓經(jīng)濟(jì)變得更有韌性。盡管我們不完全了解經(jīng)濟(jì)運(yùn)行動(dòng)態(tài)，但該如何改革經(jīng)濟(jì)的普遍教訓(xùn)似乎是顯而易見的。如果杠桿不那么高，尤其是如果減少對(duì)高杠桿金融中介機(jī)構(gòu)(即銀行)所有的風(fēng)險(xiǎn)資產(chǎn)支持的資金的依賴，經(jīng)濟(jì)的韌性將會(huì)增強(qiáng)。顯而易見的解決方案包括消除我們稅收體系中鼓勵(lì)使用杠桿的激勵(lì)措施、鼓勵(lì)擴(kuò)大經(jīng)濟(jì)對(duì)股權(quán)融資以及可輕易轉(zhuǎn)換為股權(quán)的債務(wù)的使用、提高銀行的準(zhǔn)備金和資本金要求、以及快速轉(zhuǎn)向發(fā)行央行數(shù)字貨幣。

The analysis of fundamental macroeconomic theory suggests substantial ignorance of how our economies work. This is not that surprising. We may never understand how such complex systems — animated, as they are, by human desires and misunderstandings — actually function. This does not mean that attempting to improve understanding is a foolish exercise. On the contrary, it is important. But it is arguably more vital in practice to focus on two other tasks. The first is how to make the body economic more resistant to the consequences of manias and panics. The second is how to restore it to health as quickly as possible. On both counts, we need to think more and do more. These are the practical challenges before us.

對(duì)基本宏觀經(jīng)濟(jì)理論的分析顯示，我們經(jīng)濟(jì)的運(yùn)行方式被極大地忽視了。這并不那么令人意外。我們可能永遠(yuǎn)不理解這些復(fù)雜的體系(由人類欲望和誤解驅(qū)動(dòng))實(shí)際上如何運(yùn)轉(zhuǎn)。這并不意味著努力提高認(rèn)識(shí)是愚蠢之舉。相反，這很重要。但實(shí)際上，關(guān)注另外兩個(gè)任務(wù)或許更為重要。第一個(gè)是如何讓經(jīng)濟(jì)更能抵御狂熱和恐慌的影響。第二個(gè)是如何盡可能快地令其恢復(fù)健康。從這兩方面來看，我們需要思考更多并采取更多行動(dòng)。這些是我們面臨的實(shí)際挑戰(zhàn)。