Gresham's law

 Gresham's law is an economic principle that states: "When a government overvalues one type of money and undervalues another, the undervalued money will leave the country or disappear from circulation into hoards, while the overvalued money will flood into circulation."   It is commonly stated as: "Bad money drives out good".

This law applies specifically when there are two forms of commodity money in circulation which are required by legal-tender laws to be accepted as having similar face values for economic transactions. The artificially overvalued money tends to drive an artificially undervalued money out of circulation and is a consequence of price control. 

 In economics, Gresham's law is a monetary principle stating that "bad money drives out good". For example, if there are two forms of commodity money in circulation, which are accepted by law as having similar face value, the more valuable commodity will disappear from circulation.

The law was named in 1858 by Henry Dunning Macleod, after Sir Thomas Gresham (1519–1579), who was an English financier during the Tudor dynasty.Gresham’s law, observation in economics that “bad money drives out good.” More exactly, if coins containing metal of different value have the same value as legal tender, the coins composed of the cheaper metal will be used for payment, while those made of more expensive metal will be hoarded or exported and thus tend to disappear from circulation. Sir Thomas Gresham, financial agent of Queen Elizabeth I, was not the first to recognize this monetary principle, but his elucidation of it in 1558 prompted the economist H.D. Macleod to suggest the term Gresham’s law in the 19th century.