Exchange rates and perfect competition

The purpose of this note is to demonstrate that the commonly held belief that incomplete and perverse pass-through are incompatible with perfect competition is wrong! To this end, we consider two types of firms both operating in two countries. The demand sides of the markets of the two countries are separated and each type of firm produces its good in one of these countries. We study the effect of an exchange-rate change on the competitive equilibrium prices in each country. When producing for the foreign market causes the same costs as producing for the home market then the law of one price holds and an exchange-rate change is completely offset by price changes. Furthermore, when cost functions neither exhibit economies nor diseconomies of scope between producing for the home and producing for the foreign market then prices move in the right directions in response to an exchange-rate change. However, with general cost structures, even in this simple perfectly competitive model, perverse directions of price changes can result from an exchange-rate change.