Under a system of bimetallism the coins made from the undervalued metal tend to go out of circulation. The reason for this is not difficult to understand, since the undervaluation of a metal means that it has higher value in the market than at the mint. Payments will be made preferably with the coins of the overvalued metal; with the result that the coins of the other metal will be used only as a last resort. Thus, when coins of two standard metals circulate side by side, the coins which are worth leas as metal than as money will tend to drive out of circulation the coins which are worth more as metal than as money. The same tendency occurs when similar standard coins are circulating, if some of them are worn more then others; also when metal money and paper money circulate, if the paper money is depreciated. We are now prepared to state what is generally known as Gresham's law, named after one of the advisers of Queen Elizabeth: When two kinds of money circulate concurrently, the poorer tends to drive the better out of circulation. An American writer puts it forcefully when he says that good money is too proud to circulate alongside poor money.