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. In an influential theoretical article, Rolnick and Weber (1986) argued that bad money would drive good money to a premium rather than driving it out of circulation. However, their research did not take into account the context in which Gresham made his observation. Rolnick and Weber ignored the influence of legal tender legislation which requires people to accept both good and bad money as if they were of equal value.They also focused mainly on the interaction between different metallic monies, comparing the relative "goodness" of silver to that of gold, which is not what Gresham was speaking of. The experiences of dollarization in countries with weak economies and currencies (for example Israel in the 1980s, Eastern Europe and countries in the period immediately after the collapse of the Soviet bloc, or South American countries throughout the late 20th and early 21st century) may be seen as Gresham's Law operating in its reverse form (Guidotti & Rodriguez, 1992), because in general the dollar has not been legal tender in such situations, and in some cases its use has been illegal.