>> You made a blanket statement that multiple-basis currencies cannot and haven't existed
> No, I said that there's no such thing as competing currencies. Having a single currency with more than one base has obviously been tried, but it didn't work.
I still say flat out that you're mistaken. We have (and have had) multiple currencies in the world, used within a single area (quite often, especially during wartime), regionally, and worldwide. How do you deal with multiple currencies? Via exchange rates. These may be floated or decreed, but they exist. Dollars, Euros, Yen, and gold are all commonly used for current-day international transactions (with a strong preference generally for US dollars, though this may change). The dollar also has special standing as the preferred reserve currency, but again, this is largely a matter of convention, liquidity, and stability.
Over historical time, there have been (usually local and smaller-scale, though not always) systems in which multiple currencies managed by multiple sovereigns circulated and were commonly used. Sometimes usage is specific to transaction types (e.g.: use currency A for large and multi-region transactions, use B generally for local/smaller transactions).
On England's tri-metalism, Adam Smith discusses this at length in On the Wealth of Nations. The standards date to Roman times (copper basis), with silver emerging from the Saxon tribes, and gold from mainland Europe.
> No, I said that there's no such thing as competing currencies. Having a single currency with more than one base has obviously been tried, but it didn't work.
I still say flat out that you're mistaken. We have (and have had) multiple currencies in the world, used within a single area (quite often, especially during wartime), regionally, and worldwide. How do you deal with multiple currencies? Via exchange rates. These may be floated or decreed, but they exist. Dollars, Euros, Yen, and gold are all commonly used for current-day international transactions (with a strong preference generally for US dollars, though this may change). The dollar also has special standing as the preferred reserve currency, but again, this is largely a matter of convention, liquidity, and stability.
Over historical time, there have been (usually local and smaller-scale, though not always) systems in which multiple currencies managed by multiple sovereigns circulated and were commonly used. Sometimes usage is specific to transaction types (e.g.: use currency A for large and multi-region transactions, use B generally for local/smaller transactions).
On England's tri-metalism, Adam Smith discusses this at length in On the Wealth of Nations. The standards date to Roman times (copper basis), with silver emerging from the Saxon tribes, and gold from mainland Europe.