General equilibrium ain’t just peanuts. With the tremendous shortfall in the peanut harvest (a decline of 17%) due to the unusually dry weather in peanut-growing states, people are expecting a rise in the price of this main input of peanut butter to cause supply to shift leftward. Jif peanut butter expects to raise its price by 30% starting in November.
I doubt that its sales will go down much—I think the demand for peanut butter is fairly inelastic. But what about related markets? If everyone likes peanut butter and mayonnaise sandwiches as much as I do—if peanut butter and mayonnaise are complements—then we’ll see a leftward shift in demand for mayonnaise, and its price will decline. Have I held too much of the ceteris paribus, or not enough? Where should one stop?