The modern monetary theories on short-term exchange rate volatility take into consideration the short-term capital markets' role and the long-term impact of the commodity markets on foreign exchange. These theories hold that the divergence between the exchange rate and the purchasing power parity is due to the supply and demand for financial assets and the international capability.
One of the modern monetary theories states that exchange rate volatility is triggered by a one-time domestic money supply increase, because this is assumed to raise expectations of higher future monetary growth.
The purchasing power parity theory is extended to include the capital markets. If, in both countries whose currencies are exchanged, the demand for money is determined by the level of domestic income and domestic interest rates, then a higher income increases demand for transactions balances while a higher interest rate increases the opportunity cost of holding money, reducing the demand for money.
Under a second approach, the exchange rate adjusts instantaneously to maintain continuous interest rate parity, but only in the long run to maintain purchasing power parity.
Volatility occurs because the commodity markets adjust more slowly than the financial markets. This version is known as the dynamic monetary approach.
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