Gresham's law
Copernicus for years advised the Royal Prussian sejmik on monetary reform, particularly in the 1520s when that was a major question in regional Prussian politics. In 1526 he wrote a study on the value of money, "Monetae cudendae ratio". In it he formulated an early iteration of the theory, now called Gresham's law, that "bad" (debased) coinage drives "good" (un-debased) coinage out of circulation—several decades before Thomas Gresham. He also, in 1517, set down a quantity theory of money, a principal concept in economics to the present day. Copernicus's recommendations on monetary reform were widely read by leaders of both Prussia and Poland in their attempts to stabilize currency.