Liquidity Traps: A Unified Theory of the Great Depression and the Great Recession
统一分析美国大萧条、大衰退和日本长期衰退，研究自然利率为负的暂时与永久因素，并解释零利率下限下政策效果如何取决于货币财政体制和央行可信度。
This review of liquidity traps unifies three landmark economic downturns—the US Great Depression, the Great Recession, and Japan’s Long Recession—into a single analytical framework. We examine various forces that drive natural interest rates negative: temporarily (such as banking crises and debt overhangs) or permanently (such as demographic shifts and inequality). When policy rates hit the zero lower bound, conventional monetary tools lose traction. Under a standard monetary policy regime, counterintuitive paradoxes emerge: Greater price flexibility deepens recessions, and positive supply shocks become contractionary. We show how policy effects—including the size of fiscal multipliers, forward guidance, and these paradoxes—depend critically on the monetary-fiscal regime and on central bank credibility. The paper explains how regime changes, such as Franklin D. Roosevelt’s 1933 abandonment of the gold standard and balanced-budget dogmas, successfully reversed deep slumps by credibly shifting expectations. We examine whether secular-stagnation forces are likely to assert themselves in the coming decades.