Throughout the fifteenth century, the Ming court was looking for a kind of money which was both accepted by the government and the populace. It seemed to be successful during the reign of the Chenghua emperor who, with the intention of increasing tax income, allowed merchants to pay part of their customs duties, which had been paid in paper money, in copper coins. Copper coins were the market money of the time, but the new practice caused a phenomenon of ”bad money drives out good”. The quality of cash deteriorated and it market price dropped. At last, avoiding losing revenue, some local officials privately levied the tax in silver in lieu of the coins. This was the starting of the so-called ”Single Whip Reform”.