Currency relative values of the different currencies. Currencies in this sense are defined by governments, and each type has limited boundaries of acceptance. Other definitions of the term "currency" are discussed in their respective synonymous articles banknote, coin, and money. The latter definition, pertaining to the currency systems of nations, is the topic of this article. Currencies can be classified into two monetary systems: fiat money and commodity money, depending on what guarantees the value (the economy at large vs. the government's physical metal reserves). Some currencies are legal tender in certain political jurisdictions. Others are simply traded for their economic
Shall and will and "should" function as past tenses of "will" and "shall", their usage tends to correspond to that of the latter verbs ("would" is used analogously to "will", and "should" to "shall"). Thus "would" and "should" can be used with "future-in-the-past" meaning, to express what was expected to happen, or what in fact did happen, after some past time of reference. The use of "should" here (like that of "shall" as a plain future marker) is much less common and is generally confined to the first person. Examples: "Would" can also be used as the past equivalent of "will" in its