This paper's model is capable of explaining the empirical evidence on the mixed growth‐rate effects of fiscal and monetary policies and a nonlinear inflation–growth relation. When monopoly power in the product market is strong/weak, an increase in the money growth rate or the income tax rate promotes/reduces the output growth rate through lowering/raising the equilibrium gross markup and increasing/reducing the net rate of return on capital. The fact that money can generate a positive growth rate effect allows for the appearance of a nonlinear inflation–growth relation. Such a nonlinear relation cannot be caused by changes in the income tax rate.