What Gresham's Law states, in more scientific terms, is that when government compulsorily overvalues one money and undervalues another, the undervalued (good) money will leave the country or disappear into hoards, while the overvalued (bad) money will flood into circulation. Another way of putting it is that when a circulating currency consists of both "good" and "bad" money, and legal tender law requires both forms to be accepted at equal value, the circulating currency will quickly become dominated by the "bad" money, because consumers will hand over the "bad" coins, keeping the "good" ones for themselves.
Gresham was not by any means the first to postulate this "law"; others, including the astronomer Nicolaus Copernicus (who died in 1543) had known about it for years. It was attributed to Gresham because he urged Elizabeth I to restore the debased currency of England.
© Haydn Thompson 2018