What should money be?

To be as useful as possible,money should be fungible, durable, portable, recognisable and stable. 

Being fungible means it can be replaced by an identical item. That is, it is mutually interchangeable with one another, as the units of the good are relatively uniform quality. Being durable allows money to retain its usefulness and allow it to be used numerous times. It is critical that all money is durable so it can continue to perform the related functions of store of value and medium of exchange. Users of durable money expect that once they receive the money as payment for one good, they can then use that same money to trade at a later date for another good. Being portable means it can be separated and divisible into smaller quantities. Being recognisable means that the users of the given money recognise the authenticity and quantity of the goods easily, so they can agree to the terms of exchange. Being stable means that the value should be relatively constant or increasing over time, as volatility or a currency that consistently loses value over time becomes less suitable.