Yep...if you read about the history of paper money it started out as actual promissory notes that were redeemable as gold coinage which was considered "lawful money". Hence the "gold standard" was born where all promissroy notes had to be backed up with gold. We have long since abandoned this principle unfortunately. The paper was easier to carry and transfer but was not originally considered to be legal money. It was and still is made of paper with a high linen content which gives it incredible longevity.