Look at a coin from your pocket. On one side is "heads" - the symbol of the political authority which minted the coin; on the other side is "tails" - the precise specification of the amount the coin is worth as payment in exchange.
One side reminds us that states underwrite currencies and the money is originally a relation between persons in society, a token perhaps. The other reveals the coin as a thing, capable of entering into definite relations with other things.
K. Hart