This paper demonstrates that deviations from purchasing power parity reveal a remarkable and possibly startling consistency with martingale behavior during both fixed and flexible rate periods, for a wide variety of countries, and in both monthly and annual data. Since this pattern appears to be much more general than one would expect on the basis of models founded on international commodity arbitrage, the paper proposes an alternative explanation which instead relies on financial arbitrage in bonds as the underlying mechanism.

A currency is not risky because devaluation is highly likely. If the devaluation were certain, there would be no risk at all. A weak currency can be less risky than a strong currency. A strong currency does not become risky because it has been used to denominate a firm's debt.