The whole point of fiat currency is that the stock of it can grow faster than a commodity/gold based currency (which must be mined, giving it a limited amount of growth). The growth of a currency is supposed to be fast enough to match the growing of an economy.
Both systems have faults. A gold based economy can cause deflation when the rate of mining is less than the rate of economic growth. A fiat currency can be manipulated to cause inflation if it is printed at a rate greater than economic growth.