Inflation is defined as a sustained increase in the price level or a fall in the value of money. It can be caused by an increase in the money supply exceeding real economic growth (monetarist view) or by increases in production costs pushing prices up (Keynesian view). Inflation is measured by changes in a price index like the consumer price index. It can have both favorable impacts like higher profits and investment, and unfavorable impacts like a reduction in purchasing power for those with fixed incomes. Governments use monetary, fiscal, and direct policies to control inflation by reducing excess demand or stabilizing production costs.