When Borch's Theorem Does Not Apply: Some Key Implications of Market Incompleteness,with Policy Relevance Today

Markets are incomplete when the assets available to the agents do not span the space of future contingencies. In that case, competitive equilibria on the markets for assets and commodities fail (generically) to be constrained efficient. Pareto‐superior allocations can be implemented through price/wage rigidities and quantity constraints. However, nominal rigidities are conducive to multiple equilibria, implying endogenous macroeconomic uncertainties that compound the primitive (exogenous) uncertainties. This paper defines a temporary general equilibrium for which there exists a set of equilibria defining an inflation – unemployment locus. Various policy implications are drawn, with relevance to the current crisis.