Bad money drives out good money.
Gresham’s law is an economics principle. If, for example there are two coins in circulation containing metal of different value and which are accepted by law as having similar face value, the more valuable coin based on the inherent value of its component metals will gradually disappear from circulation.
The law was named in 1857 by economist Henry Dunning Macleod after Sir Thomas Gresham (1519–1579), an English financier during the Tudor dynasty. Gresham had urged Queen Elizabeth to restore confidence in the then-debased English currency.