Currencies have their value nominally defined by a sovereign power. Some currencies in the past used precious metals in coinage, but that didn't determine it's

Currencies have their value nominally defined by a sovereign power. Some currencies in the past used precious metals in coinage, but that didn't determine it's value. Value of currency can be changed according to policy. As such gold has never been a currency, but has been a commodity used in some coinage. The discussion is "nominalism" versus "metalism". Nominalism wins by a country mile! Gold backed currencys, similarly to currencys who tie their value to a different currency (such as pegging exchange rates) only serve to reduce the capacity of the issuing body to pursue domestic policy in the interests of the populous. In that sense, a commodity can be a store of value that's not a currency, and can be used as material to represent currency, but cannot be a currency.