Shocks and Business Cycles.

A popular theory of business cycles is that they are driven by animal spirits: shifts in expectations brought on by sunspots. Two prominent examples are Diamond (JPE, 1982) and Howitt and McAfee (AER, 1992). We show that these models have unique equilibria if there are payoff shocks of any size. At critical junctures, a small negative shock can cause the economy to slide into a recession. Once this happens, a sustained sequence of positive shocks is needed to spark an expansion.