[barrkel]

> - A medium of exchange

> - A store of value

> - A unit of account

Note that these are all social attributes. They are true because and only because society treats them so. A medium of exchange works because counterparties to the exchange accept the medium. A store of value works because counterparties in the near future will accept the currency at something similar to its current value - its value isn't heavily fluctuating. And a unit of account works because people physically write up accounts using the currency as a unit, issue invoices and demand payment using the unit, issue debt and demand interest, borrow and pay interest, all using the unit.

It's all a social construct.

(Gold's value is a social construct too, of course.)