Limits on policy effects[edit]
Although the perception by the public may be that the "central bank" controls some or all interest rates and currency rates, economic theory (and substantial empirical evidence) shows that it is impossible to do both at once in an open economy. Robert Mundell's "impossible trinity" is the most famous formulation of these limited powers, and postulates that it is impossible to target monetary policy (broadly, interest rates), the exchange rate (through a fixed rate) and maintain free capital movement. Since most Western economies are now considered "open" with free capital movement, this essentially means that central banks may target interest rates or exchange rates with credibility, but not both at once.
In the most famous case of policy failure, Black Wednesday, George Soros arbitraged the pound sterling's relationship to the ECU and (after making $2 billion himself and forcing the UK to spend over $8bn defending the pound) forced it to abandon its policy. Since then he has been a harsh critic of clumsy bank policies and argued that no one should be able to do what he did.[citation needed]
The most complex relationships are those between the yuan and the US dollar, and between the euro and its neighbours. The situation in Cuba is so exceptional as to require the Cuban peso to be dealt with simply as an exception, since the United States forbids direct trade with Cuba. US dollars were ubiquitous in Cuba's economy after its legalization in 1991, but were officially removed from circulation in 2004 and replaced by the convertible peso.
Limits on policy effects[edit]
Although the perception by the public may be that the "central bank" controls some or all interest rates and currency rates, economic theory (and substantial empirical evidence) shows that it is impossible to do both at once in an open economy. Robert Mundell's "impossible trinity" is the most famous formulation of these limited powers, and postulates that it is impossible to target monetary policy (broadly, interest rates), the exchange rate (through a fixed rate) and maintain free capital movement. Since most Western economies are now considered "open" with free capital movement, this essentially means that central banks may target interest rates or exchange rates with credibility, but not both at once.
In the most famous case of policy failure, Black Wednesday, George Soros arbitraged the pound sterling's relationship to the ECU and (after making $2 billion himself and forcing the UK to spend over $8bn defending the pound) forced it to abandon its policy. Since then he has been a harsh critic of clumsy bank policies and argued that no one should be able to do what he did.[citation needed]
The most complex relationships are those between the yuan and the US dollar, and between the euro and its neighbours. The situation in Cuba is so exceptional as to require the Cuban peso to be dealt with simply as an exception, since the United States forbids direct trade with Cuba. US dollars were ubiquitous in Cuba's economy after its legalization in 1991, but were officially removed from circulation in 2004 and replaced by the convertible peso.
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