This article shows that when agents learn from prices, large private uncertainty may result from a small amount of heterogeneity. As in a Phelps–Lucas island model, final producers look at the prices of their local inputs to infer aggregate conditions. However, market linkages between islands make the informativeness of local prices endogenous to general equilibrium relations. In this context, I show that a vanishingly small heterogeneity in local conditions is enough to generate an equilibrium in which prices are rigid to aggregate shocks and transmit only partial information. I use this insight as a microfoundation for price rigidity in an otherwise frictionless monetary model and show that even a tiny amount of dispersion in fundamentals can lead to large non-neutrality of money.

We formalize the idea that house price changes may drive rational waves of optimism and pessimism in the economy. In our model, a house price increase caused by aggregate disturbances may be misinterpreted as a sign of higher local permanent income, leading households to demand more consumption and housing. Higher demand reinforces the initial price increase in an amplification loop that drives comovement in output, labour, residential investment, land prices, and house prices even in response to aggregate supply shocks. The qualitative implications of our otherwise frictionless model are consistent with observed business cycles and it can explain the economic impact of apparently autonomous changes in sentiment without resorting to non-fundamental shocks or nominal rigidity.