In the presence of frictions, the existing literature shows that currency substitution is detrimental for domestic aggregate stability. This paper singles out the role of currency substitution and shows that diversified currency holdings operate as an automatic stabilizer that mitigates belief-driven cyclical fluctuations in Farmer’s (1997) indeterminate monetary economy. When the foreign inflation rate is lower than the domestic inflation rate, the model’s steady state always displays saddle-path stability. Hence, equilibrium indeterminacy originally present in the domestic country is entirely removed in the presence of diversified currency holdings. When the foreign inflation rate is higher than the domestic inflation rate, then depending on the degrees of currency substitution and relative risk aversion, indeterminacy is either impossible or the requisite level of the foreign inflation rate for indeterminacy is too high to square with data. The stabilizing effect of diversified currency holdings on domestic aggregate stability is robust to whether domestic and foreign currencies display as Edgeworth substitutes or complements, or are additively separable in the household’s preferences.

Benhabib and Farmer show that in a laissez-faire one-sector real business cycle model under aggregate increasing returns, under sufficiently high degrees of productive externality, the demand-side effect in the labor market triggered by agents' expectations about the economy's future outweighs the supply-side effect, making agents' expectations become self-fulfilling. This paper analytically demonstrates that the conduct of monetary policy under nominal gross domestic product (GDP) targeting reinforces the supply-side effect in the labor market, thereby making belief-driven aggregate fluctuations more difficult to occur. This reinforcement effect on labor supply is absent under nominal consumption targeting and inflation targeting. Hence, under these two monetary regimes, the necessary and sufficient conditions for the economy to display equilibrium indeterminacy and sunspot fluctuations are identical to those in Benhabib and Farmer's laissez-faire economy. The results are robust to an endogenous growth extension of the model, implying that targeting the nominal GDP growth rate is more desirable than targeting the nominal consumption growth rate or the inflation rate in terms of macroeconomic stability.