Indebtedness may also be covered by a simple IOU which states the amount owed by an individual while a promissory note contains the amount, the steps needed to go through to pay the indebtedness and the consequences of late payment or failure to pay.
There were periods in history where promissory notes have been used as an alternate currency, circulating free from government controls. There were places where the currency used was a promissory note known as a demand promissory note, with no maturity date. These promissory notes allowed the lender to demand payment when he has decided to do so.