翻譯：陳達(dá)飛      摘自Richard Koo（2018）

Obsession with Mathematics Is Killing Macroeconomics’ Credibility

對數(shù)學(xué)的癡迷正在扼殺宏觀經(jīng)濟(jì)學(xué)的可信度

The reliance on universal substitutability became essential when mathematical modeling became an obsession (or fad) formainstream economists. Today, many in the profession would not consider anything that is not expressed in mathematical terms (such as this book) to be serious economics. But for mathematical equations to be useful (i.e.,differentiable), models have to assume universal substitutability so that the behavioral changes of economic agents remain smooth and continuous. That, inturn, makes these models useless when households and businesses are forced tomake abrupt changes or even reverse their behavior because of balance sheet concerns or other problems.

當(dāng)數(shù)學(xué)建模成為主流經(jīng)濟(jì)學(xué)家的一種時(shí)尚時(shí)，對普遍可替代性假設(shè)（比如假設(shè)相對價(jià)格的變化總會在經(jīng)濟(jì)中引起反應(yīng)，可參考Markey-Towler, Brendan (2017a) Foundations for Economic Analysis:The Architecture of Socioeconomic Complexity, Ph.D thesis, School of Economics,University of Queensland.）的依賴變得至關(guān)重要。如今，許多經(jīng)濟(jì)學(xué)家認(rèn)為，任何不是用數(shù)學(xué)術(shù)語表達(dá)的東西(比如這本書)都不是嚴(yán)肅的經(jīng)濟(jì)學(xué)。但要使得數(shù)學(xué)方程有用（或可微分），模型必須假設(shè)普遍可替代性，使經(jīng)濟(jì)主體的行為變化保持平穩(wěn)和連續(xù)。因此，當(dāng)家庭和企業(yè)因?yàn)橘Y產(chǎn)負(fù)債表問題或其他問題而被迫做出突然的改變時(shí)，或者是行為出現(xiàn)反轉(zhuǎn)時(shí)，這些模型就毫無用處了。

Economists such as Eggertsson and Krugman(2012) have argued that their models indicate that monetary easing is still effective even in a Fisher–Minsky–Koo environment, and that inflation targeting and quantitative easing (QE) should work. The fact that Krugman himself admitted three years later that these policies have failed to be “game changers” in the real world suggests that their models and equations did notfully incorporate the possibility that universal substitutability would notonly disappear but also change signs following a bubble collapse.

Eggertsson和Krugman(2012)等經(jīng)濟(jì)學(xué)家認(rèn)為，他們的模型表明，即使在費(fèi)雪-明斯基-辜朝明框架下，貨幣寬松政策仍然有效，通脹目標(biāo)制和量化寬松(QE)是有效的。克魯格曼本人在三年后承認(rèn)，這些政策在現(xiàn)實(shí)世界中未能成為“游戲改變者”。這一事實(shí)表明，他們的模型和方程式?jīng)]有充分考慮到這樣一種可能性：在泡沫破裂后，普遍的可替代性不僅會消失，而且還會改變方向。

In view of the fact that the discipline ofmacroeconomics was born in the midst of the most abrupt shift to debtminimization in history, the Great Depression, the use of mathematics thatcannot accommodate such disconnects in human behavior makes little sense. Thefact that only a few economists were able to predict the Great Recession andits long and unpleasant aftermath says a lot about the usefulness ofmathematical tools in understanding the economy.

鑒于宏觀經(jīng)濟(jì)學(xué)這門學(xué)科誕生于歷史上最突然的債務(wù)最小化(即“大蕭條”)時(shí)期，用數(shù)學(xué)來解釋人類行為中的這種不連續(xù)性毫無意義。只有少數(shù)經(jīng)濟(jì)學(xué)家能夠預(yù)測大衰退及其漫長而令人不快的余波，這一事實(shí)充分說明了數(shù)學(xué)工具在理解經(jīng)濟(jì)方面的有效性如何。

The advanced mathematics used in astrophysics succeeded in landing a man on the moon. The advanced mathematics used in economics (and the professors who ply the trade) failed to predict notonly the biggest macroeconomic event since the Great Depression and the birth of macroeconomics, but also the substantial changes to the effectiveness of monetary and fiscal policy after 2008.

應(yīng)用于天體物理學(xué)的高等數(shù)學(xué)成功地使人類登上了月球，經(jīng)濟(jì)學(xué)中使用的高等數(shù)學(xué)(以及從事這一行業(yè)的教授們)不僅未能預(yù)測出自大蕭條和宏觀經(jīng)濟(jì)學(xué)誕生以來最大的宏觀經(jīng)濟(jì)事件，也未能預(yù)測到2008年后貨幣和財(cái)政政策有效性的重大變化。

Astrophysicists could land a man on the moon because the moon does not change direction abruptly. Economists failed topredict the Great Recession because people react to events and change directionall the time. And some of those changes can happen quite abruptly. By relying on mathematics as their primary tool, economists are often treating people as they would treat planetary objects like the moon or Mars, and not as thinking and reacting individuals.

天體物理學(xué)家可以把人送上月球，因?yàn)樵虑虿粫蝗桓淖兎较?。?jīng)濟(jì)學(xué)家未能預(yù)測到大衰退，因?yàn)槿藗兛偸菍κ录龀龇磻?yīng)并不斷改變方向。有些變化可能發(fā)生得非常突然。依靠數(shù)學(xué)作為他們的主要工具，經(jīng)濟(jì)學(xué)家經(jīng)常像對待月球或火星這樣的行星一樣對待人，而非有思考能力和又反應(yīng)能力的個體。

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