We propose a new model of the macroeconomy which is simple and tractable, yet explicit about the foundations of liquidity. Monetary policy is implemented via swaps of money for liquid bonds in a secondary asset market. Prices are flexible, yet policy has real effects because money, bonds, and capital are imperfect substitutes, both in the short run and in the long run. The model unifies two classical channels through which the price of liquidity affects the economy (Friedman's real balance effect vs Mundell's and Tobin's asset substitution effect), and it shines light on important macroeconomic questions: the causal link between interest rates and inflation, the effects of money demand shocks, and the existence and persistence of a liquidity trap where interest rates are zero but inflation is positive.

我们提出了一种新的宏观经济模型，该模型简单易行，但对流动性的基础很明确。货币政策是通过在二级资产市场上用货币互换流动性债券来实施的。价格是灵活的，但政策具有实际效果，因为货币、债券和资本在短期和长期都是不完美的替代品。该模型统一了流动性价格影响经济的两个经典渠道（弗里德曼的实际平衡效应与蒙代尔和托宾的资产替代效应），并阐明了重要的宏观经济问题：利率和通货膨胀之间的因果关系，货币需求冲击，以及利率为零但通货膨胀为正的流动性陷阱的存在和持续存在。