Beijing

IN giving markets a greater say in setting the yuan's level, central bank governor Zhou Xiaochuan is bowing to Nobel Prize-winning economist Robert Mundell's maxim that a country can't maintain independent monetary policy, a fixed exchange rate and free capital borders all at the same time.

The policy trilemma, or impossible trinity, is illustrated by Asia's experience in the 1990s. When some countries violated the dictum, their pegged currencies, high interest rates and open capital borders attracted a flood of foreign investment that quickly reversed along with their trade balances, triggering the Asian financial crisis of 1997-98.