The certificate is considered representative money. The money Troy is using is fiat money. The money Sky is using is commodity money.
Representative money is any form of exchange that will represent value but has not value of its own. Since the certificate is good for a dollar amount but does not actually hold that value elsewhere, it is considered representative money. Fiat money is inconvertible paper money that the government creates. This money is not backed by anything physical but has a value. Commodity money holds a value from which the commodity was made. Commodity money is a medium of exchange that has representation such as clothes, silver, gold etc.
