翻译：陈达飞 摘自Richard Koo（2018）
Obsession with Mathematics Is Killing Macroeconomics’ Credibility
对数学的痴迷正在扼杀宏观经济学的可信度
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.
当数学建模成为主流经济学家的一种时尚时，对普遍可替代性假设（比如假设相对价格的变化总会在经济中引起反应，可参考Markey-Towler, Brendan (2017a) Foundations for Economic Analysis:The Architecture of Socioeconomic Complexity, Ph.D thesis, School of Economics,University of Queensland.）的依赖变得至关重要。如今，许多经济学家认为，任何不是用数学术语表达的东西(比如这本书)都不是严肃的经济学。但要使得数学方程有用（或可微分），模型必须假设普遍可替代性，使经济主体的行为变化保持平稳和连续。因此，当家庭和企业因为资产负债表问题或其他问题而被迫做出突然的改变时，或者是行为出现反转时，这些模型就毫无用处了。
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)等经济学家认为，他们的模型表明，即使在费雪-明斯基-辜朝明框架下，货币宽松政策仍然有效，通胀目标制和量化宽松(QE)是有效的。克鲁格曼本人在三年后承认，这些政策在现实世界中未能成为“游戏改变者”。这一事实表明，他们的模型和方程式没有充分考虑到这样一种可能性：在泡沫破裂后，普遍的可替代性不仅会消失，而且还会改变方向。
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.
鉴于宏观经济学这门学科诞生于历史上最突然的债务最小化(即“大萧条”)时期，用数学来解释人类行为中的这种不连续性毫无意义。只有少数经济学家能够预测大衰退及其漫长而令人不快的余波，这一事实充分说明了数学工具在理解经济方面的有效性如何。
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.
应用于天体物理学的高等数学成功地使人类登上了月球，经济学中使用的高等数学(以及从事这一行业的教授们)不仅未能预测出自大萧条和宏观经济学诞生以来最大的宏观经济事件，也未能预测到2008年后货币和财政政策有效性的重大变化。
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.
天体物理学家可以把人送上月球，因为月球不会突然改变方向。经济学家未能预测到大衰退，因为人们总是对事件做出反应并不断改变方向。有些变化可能发生得非常突然。依靠数学作为他们的主要工具，经济学家经常像对待月球或火星这样的行星一样对待人，而非有思考能力和又反应能力的个体。
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